netcdf-c/man4/netcdf-c.texi

\input texinfo @c -*-texinfo-*-
@c $Id: netcdf-c.texi,v 1.116 2010/02/01 00:25:20 russ Exp $
@c %**start of header
@setfilename netcdf-c.info
@setcontentsaftertitlepage
@settitle NetCDF C Interface Guide
@c Combine the variable, concept, and function indices.
@synindex vr cp
@synindex fn cp
@c %**end of header

@include version-c.texi
@include defines.texi

@ifinfo
@dircategory netCDF scientific data format
@direntry
* netcdf-c: (netcdf-c).         @value{c-man}
@end direntry
@end ifinfo

@titlepage
@title @value{c-man}
@subtitle NetCDF Version @value{VERSION}
@subtitle Last Updated @value{UPDATED}
@author Russ Rew, Glenn Davis, Steve Emmerson, Harvey Davies, and Ed Hartnett
@author Unidata Program Center
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@ifnottex
@node Top, Use of the NetCDF Library, (dir), (dir)
@top @value{c-man}
@end ifnottex

This document describes the C interface to the netCDF library; it
applies to netCDF version @value{VERSION} and was last updated on
@value{UPDATED}.

For a complete description of the netCDF format and utilities see 
@ref{Top, @value{n-man},, netcdf, @value{n-man}}.

@menu
* Use of the NetCDF Library::   
* Datasets::                    
* Groups::                      
* Dimensions::                  
* User Defined Data Types::     
* Variables::                   
* Attributes::                  
* Summary of C Interface::      
* NetCDF 3 Transition Guide::   
* NetCDF 2 C Transition Guide::  
* NetCDF-3 Error Codes::        
* NetCDF-4 Error Codes::        
* DAP Error Codes::             
* Combined Index::              

@detailmenu
 --- The Detailed Node Listing ---

Use of the NetCDF Library

* Creating::                    Creating a NetCDF Dataset                    
* Reading Known ::              Reading a NetCDF Dataset with Known Names        
* Reading Unknown ::            Reading a netCDF Dataset with Unknown Names
* Adding::                      Adding New Dimensions, Variables, Attributes        
* Errors::                      Error Handling        
* Compiling::                   Compiling and Linking with the NetCDF Library        

Datasets

* Interface Descriptions::      What's in the Function Documentation
* parallel access::             
* nc_strerror::                 Get Error Messages
* nc_inq_libvers::              Get netCDF library version
* nc_create::                   Create a Dataset
* nc__create::                  Create a Dataset with Performance Tuning
* nc_create_par::               
* nc_open::                     Open a Dataset
* nc__open::                    Open a Dataset with Performance Tuning
* nc_open_par::                 
* nc_redef::                    Put a Dataset into Define Mode
* nc_enddef::                   Leave Define Mode
* nc__enddef::                  Leave Define Mode with Performance Tuning
* nc_close::                    Close a Dataset
* nc_inq Family::               Inquire about a Dataset
* nc_sync::                     Synchronize a Dataset to Disk
* nc_abort::                    Back Out of Recent Definitions
* nc_set_fill::                 Set Fill Mode for Writes
* nc_set_default_format::       Change the default output format
* nc_set_chunk_cache::          
* nc_get_chunk_cache::          

Groups

* nc_inq_ncid::                 
* nc_inq_grps::                 
* nc_inq_varids::               
* nc_inq_dimids::               
* nc_inq_grpname::              
* nc_inq_grpname_full::         
* nc_inq_grpname_len::          
* nc_inq_grp_parent::           
* nc_inq_grp_ncid::             
* nc_inq_grp_full_ncid::        
* nc_def_grp::                  

Dimensions

* Dimensions Introduction::     
* nc_def_dim::                  Create a Dimension
* nc_inq_dimid::                Get a Dimension ID from Its Name
* nc_inq_dim Family::           Inquire about a Dimension
* nc_rename_dim::               Rename a Dimension
* nc_inq_unlimdims::            

User Defined Data Types

* User Defined Types::          
* nc_inq_typeids::              
* nc_inq_typeid::               
* nc_inq_type::                 
* nc_inq_user_type::            
* Compound Types::              
* nc_def_compound::             
* nc_insert_compound::          
* nc_insert_array_compound::    
* nc_inq_compound::             
* nc_inq_compound_name::        
* nc_inq_compound_size::        
* nc_inq_compound_nfields::     
* nc_inq_compound_field::       
* nc_inq_compound_fieldname::   
* nc_inq_compound_fieldindex::  
* nc_inq_compound_fieldoffset::  
* nc_inq_compound_fieldtype::   
* nc_inq_compound_fieldndims::  
* nc_inq_compound_fielddim_sizes::  
* Variable Length Array::       
* nc_def_vlen::                 
* nc_inq_vlen::                 
* nc_free_vlen::                
* nc_free_vlens::               
* Opaque Type::                 
* nc_def_opaque::               
* nc_inq_opaque::               
* Enum Type::                   
* nc_def_enum::                 
* nc_insert_enum::              
* nc_inq_enum::                 
* nc_inq_enum_member::          
* nc_inq_enum_ident::           

Compound Types Introduction

* nc_def_compound::                  
* nc_insert_compound::               
* nc_inq_compound::                  
* nc_inq_compound_fieldname::        
* nc_inq_compound_fieldindex::       
* nc_inq_compound_fieldoffset::      
* nc_inq_compound_fieldtype::        

Variables

* Variable Introduction::       
* Variable Types::              
* NetCDF-3 Variable Types::     
* NetCDF-4 Atomic Types::       
* nc_def_var::                  Create a Variable
* nc_def_var_chunking::         Set chunking parameters
* nc_inq_var_chunking::         Learn about chunking parameters
* nc_set_var_chunk_cache::      
* nc_get_var_chunk_cache::      
* nc_def_var_fill::             
* nc_inq_var_fill::             
* nc_def_var_deflate::          Set compression parameters
* nc_inq_var_deflate::          Learn about compression parameters
* nc_inq_var_szip::             
* nc_def_var_fletcher32::       Set checksum filter
* nc_inq_var_fletcher32::       Learn if checksum filter is set
* nc_def_var_endian::           
* nc_inq_var_endian::           
* nc_inq_varid::                Get a Variable ID from Its Name
* nc_inq_var::                  Get Information about a Variable from Its ID
* nc_put_var1_ type::           Write a Single Data Value
* nc_put_var_ type::            Write an Entire Variable
* nc_put_vara_ type::           Write an Array of Values
* nc_put_vars_ type::           Write a Subsampled Array of Values
* nc_put_varm_ type::           Write a Mapped Array of Values
* nc_get_var1_ type::           Read a Single Data Value
* nc_get_var_ type::            Read an Entire Variable
* nc_get_vara_ type::           Read an Array of Values
* nc_get_vars_ type::           Read a Subsampled Array of Values
* nc_get_varm_ type::           Read a Mapped Array of Values
* Strings::                     Reading and Writing Character String Values
* nc_free_string::              
* Fill Values::                 What's Written Where there's No Data?
* nc_rename_var::               Rename a Variable
* nc_copy_var::                 
* nc_var_par_access::           
* nc_var_ubyte::                

Reading and Writing Character String Values

* Classic Strings::             
* Arrays of Strings::           

Attributes

* Attributes Introduction::     
* nc_put_att_ type::            
* nc_inq_att Family::           
* nc_get_att_ type::            
* nc_copy_att::                 
* nc_rename_att::               
* nc_del_att::                  

@end detailmenu
@end menu

@node Use of the NetCDF Library, Datasets, Top, Top
@chapter Use of the NetCDF Library
@findex nc_create, typical use
@findex nc_def_dim, typical use
@findex nc_def_var, typical use
@findex nc_put_att, typical use
@findex nc_enddef, typical use
@findex nc_put_var, typical use
@findex nc_close, typical use
@cindex creating a dataset
@cindex abnormal termination
@cindex call sequence, typical
@cindex templates, code
@cindex code templates
@vindex NC_SHARE, and buffering

You can use the netCDF library without knowing about all of the netCDF
interface. If you are creating a netCDF dataset, only a handful of
routines are required to define the necessary dimensions, variables,
and attributes, and to write the data to the netCDF dataset. (Even
less is needed if you use the ncgen utility to create the dataset
before running a program using netCDF library calls to write data.)
Similarly, if you are writing software to access data stored in a
particular netCDF object, only a small subset of the netCDF library is
required to open the netCDF dataset and access the data. Authors of
generic applications that access arbitrary netCDF datasets need to be
familiar with more of the netCDF library.

In this chapter we provide templates of common sequences of netCDF
calls needed for common uses. For clarity we present only the names of
routines; omit declarations and error checking; omit the type-specific
suffixes of routine names for variables and attributes; indent
statements that are typically invoked multiple times; and use ... to
represent arbitrary sequences of other statements. Full parameter
lists are described in later chapters.

@menu
* Creating::                    Creating a NetCDF Dataset                    
* Reading Known ::              Reading a NetCDF Dataset with Known Names        
* Reading Unknown ::            Reading a netCDF Dataset with Unknown Names
* Adding::                      Adding New Dimensions, Variables, Attributes        
* Errors::                      Error Handling        
* Compiling::                   Compiling and Linking with the NetCDF Library        
@end menu

@node Creating, Reading Known , Use of the NetCDF Library, Use of the NetCDF Library
@section Creating a NetCDF Dataset

Here is a typical sequence of netCDF calls used to create a new netCDF dataset:

@example
    nc_create           /* create netCDF dataset: enter define mode */
         ... 
       nc_def_dim       /* define dimensions: from name and length */
         ... 
       nc_def_var       /* define variables: from name, type, ... */
         ... 
       nc_put_att       /* put attribute: assign attribute values */
         ... 
    nc_enddef           /* end definitions: leave define mode */
         ... 
       nc_put_var       /* provide values for variables */
         ... 
    nc_close            /* close: save new netCDF dataset */
@end example

Only one call is needed to create a netCDF dataset, at which point you
will be in the first of two netCDF modes. When accessing an open
netCDF dataset, it is either in define mode or data mode. In define
mode, you can create dimensions, variables, and new attributes, but
you cannot read or write variable data. In data mode, you can access
data and change existing attributes, but you are not permitted to
create new dimensions, variables, or attributes.

One call to nc_def_dim is needed for each dimension
created. Similarly, one call to nc_def_var is needed for each variable
creation, and one call to a member of the nc_put_att family is needed
for each attribute defined and assigned a value. To leave define mode
and enter data mode, call nc_enddef.

Once in data mode, you can add new data to variables, change old
values, and change values of existing attributes (so long as the
attribute changes do not require more storage space). Single values
may be written to a netCDF variable with one of the members of the
nc_put_var1 family, depending on what type of data you have to
write. All the values of a variable may be written at once with one of
the members of the nc_put_var family. Arrays or array cross-sections
of a variable may be written using members of the nc_put_vara
family. Subsampled array sections may be written using members of the
nc_put_vars family. Mapped array sections may be written using members
of the nc_put_varm family. (Subsampled and mapped access are general
forms of data access that are explained later.)

Finally, you should explicitly close all netCDF datasets that have
been opened for writing by calling nc_close. By default, access to the
file system is buffered by the netCDF library. If a program terminates
abnormally with netCDF datasets open for writing, your most recent
modifications may be lost. This default buffering of data is disabled
by setting the NC_SHARE flag when opening the dataset. But even if
this flag is set, changes to attribute values or changes made in
define mode are not written out until nc_sync or nc_close is called.

@node Reading Known , Reading Unknown , Creating, Use of the NetCDF Library
@section Reading a NetCDF Dataset with Known Names
@findex nc_inq_dimid, typical use
@findex nc_inq_varid, typical use
@findex nc_get_att, typical use
@findex nc_get_var, typical use
@cindex reading netCDF dataset with known names

Here we consider the case where you know the names of not only the
netCDF datasets, but also the names of their dimensions, variables,
and attributes. (Otherwise you would have to do "inquire" calls.) The
order of typical C calls to read data from those variables in a netCDF
dataset is:

@example
    nc_open                /* open existing netCDF dataset */
         ... 
       nc_inq_dimid        /* get dimension IDs */
         ... 
       nc_inq_varid        /* get variable IDs */
         ... 
       nc_get_att          /* get attribute values */
         ... 
       nc_get_var          /* get values of variables */
         ... 
    nc_close               /* close netCDF dataset */
@end example

First, a single call opens the netCDF dataset, given the dataset name,
and returns a netCDF ID that is used to refer to the open netCDF
dataset in all subsequent calls.

Next, a call to nc_inq_dimid for each dimension of interest gets the
dimension ID from the dimension name. Similarly, each required
variable ID is determined from its name by a call to nc_inq_varid Once
variable IDs are known, variable attribute values can be retrieved
using the netCDF ID, the variable ID, and the desired attribute name
as input to a member of the nc_get_att family (typically
nc_get_att_text or nc_get_att_double) for each desired
attribute. Variable data values can be directly accessed from the
netCDF dataset with calls to members of the nc_get_var1 family for
single values, the nc_get_var family for entire variables, or various
other members of the nc_get_vara, nc_get_vars, or nc_get_varm families
for array, subsampled or mapped access.

Finally, the netCDF dataset is closed with nc_close. There is no need
to close a dataset open only for reading.

@node Reading Unknown , Adding, Reading Known , Use of the NetCDF Library
@section Reading a netCDF Dataset with Unknown Names
@findex nc_inq, typical use
@findex nc_inq_dim, typical use
@findex nc_inq_var, typical use
@findex nc_inq_att, typical use
@findex nc_get_att, typical use
@findex nc_get_var, typical use
@cindex reading netCDF dataset with unknown names

It is possible to write programs (e.g., generic software) which do
such things as processing every variable, without needing to know in
advance the names of these variables. Similarly, the names of
dimensions and attributes may be unknown.

Names and other information about netCDF objects may be obtained from
netCDF datasets by calling inquire functions. These return information
about a whole netCDF dataset, a dimension, a variable, or an
attribute. The following template illustrates how they are used:

@example
    nc_open                   /* open existing netCDF dataset */
      ... 
    nc_inq                    /* find out what is in it */
         ... 
       nc_inq_dim             /* get dimension names, lengths */
         ... 
       nc_inq_var             /* get variable names, types, shapes */
            ... 
          nc_inq_attname      /* get attribute names */
            ... 
          nc_inq_att          /* get attribute types and lengths */
            ... 
          nc_get_att          /* get attribute values */
            ... 
       nc_get_var             /* get values of variables */
         ... 
    nc_close                  /* close netCDF dataset */
@end example

As in the previous example, a single call opens the existing netCDF
dataset, returning a netCDF ID. This netCDF ID is given to the nc_inq
routine, which returns the number of dimensions, the number of
variables, the number of global attributes, and the ID of the
unlimited dimension, if there is one.

All the inquire functions are inexpensive to use and require no I/O,
since the information they provide is stored in memory when a netCDF
dataset is first opened.

Dimension IDs use consecutive integers, beginning at 0. Also
dimensions, once created, cannot be deleted. Therefore, knowing the
number of dimension IDs in a netCDF dataset means knowing all the
dimension IDs: they are the integers 0, 1, 2, ...up to the number of
dimensions. For each dimension ID, a call to the inquire function
nc_inq_dim returns the dimension name and length.

Variable IDs are also assigned from consecutive integers 0, 1, 2,
... up to the number of variables. These can be used in nc_inq_var
calls to find out the names, types, shapes, and the number of
attributes assigned to each variable.

Once the number of attributes for a variable is known, successive
calls to nc_inq_attname return the name for each attribute given the
netCDF ID, variable ID, and attribute number. Armed with the attribute
name, a call to nc_inq_att returns its type and length. Given the type
and length, you can allocate enough space to hold the attribute
values. Then a call to a member of the nc_get_att family returns the
attribute values.

Once the IDs and shapes of netCDF variables are known, data values can
be accessed by calling a member of the nc_get_var1 family for single
values, or members of the nc_get_var, nc_get_vara, nc_get_vars, or
nc_get_varm for various kinds of array access.

@node Adding, Errors, Reading Unknown , Use of the NetCDF Library
@section Adding New Dimensions, Variables, Attributes
@findex nc_redef, typical use
@findex nc_def_dim, typical use
@findex nc_put_att, typical use
@cindex dimensions, adding
@cindex variables, adding
@cindex attributes, adding
@cindex aborting define mode
@cindex aborting definitions
@cindex adding dimensions
@cindex adding attributes
@cindex adding variables
@cindex attributes, deleting, introduction
@cindex NC_SHARE

An existing netCDF dataset can be extensively altered. New dimensions,
variables, and attributes can be added or existing ones renamed, and
existing attributes can be deleted. Existing dimensions, variables,
and attributes can be renamed. The following code template lists a
typical sequence of calls to add new netCDF components to an existing
dataset:

@example
    nc_open             /* open existing netCDF dataset */
      ... 
    nc_redef            /* put it into define mode */
        ... 
      nc_def_dim        /* define additional dimensions (if any) */
        ... 
      nc_def_var        /* define additional variables (if any) */
        ... 
      nc_put_att        /* define additional attributes (if any) */
        ... 
    nc_enddef           /* check definitions, leave define mode */
        ... 
      nc_put_var        /* provide values for new variables */
        ... 
    nc_close            /* close netCDF dataset */
@end example

A netCDF dataset is first opened by the nc_open call. This call puts
the open dataset in data mode, which means existing data values can be
accessed and changed, existing attributes can be changed (so long as
they do not grow), but nothing can be added. To add new netCDF
dimensions, variables, or attributes you must enter define mode, by
calling nc_redef. In define mode, call nc_def_dim to define new
dimensions, nc_def_var to define new variables, and a member of the
nc_put_att family to assign new attributes to variables or enlarge old
attributes.

You can leave define mode and reenter data mode, checking all the new
definitions for consistency and committing the changes to disk, by
calling nc_enddef. If you do not wish to reenter data mode, just call
nc_close, which will have the effect of first calling nc_enddef.

Until the nc_enddef call, you may back out of all the redefinitions
made in define mode and restore the previous state of the netCDF
dataset by calling nc_abort. You may also use the nc_abort call to
restore the netCDF dataset to a consistent state if the call to
nc_enddef fails. If you have called nc_close from definition mode and
the implied call to nc_enddef fails, nc_abort will automatically be
called to close the netCDF dataset and leave it in its previous
consistent state (before you entered define mode).

For netCDF-4/HDF5 format files, define mode is still important, but
the user does not have to called nc_enddef - it is called
automatically when needed. It may also be called by the user.

In netCDF-4/HDF5 files, there are some settings which can only be
modified during the very first define mode of the file. For example
the compression level of a variable may be set only after the
nc_def_var call and before the next nc_enddef call, whether it is
called by the user explicitly, or when the user tries to read or write
some data.

At most one process should have a netCDF dataset open for writing at
one time. The library is designed to provide limited support for
multiple concurrent readers with one writer, via disciplined use of
the nc_sync function and the NC_SHARE flag. If a writer makes changes
in define mode, such as the addition of new variables, dimensions, or
attributes, some means external to the library is necessary to prevent
readers from making concurrent accesses and to inform readers to call
nc_sync before the next access.

@node Errors, Compiling, Adding, Use of the NetCDF Library
@section Error Handling
@findex nc_strerror, introduction
@cindex error handling
@cindex write errors

The netCDF library provides the facilities needed to handle errors in
a flexible way. Each netCDF function returns an integer status
value. If the returned status value indicates an error, you may handle
it in any way desired, from printing an associated error message and
exiting to ignoring the error indication and proceeding (not
recommended!). For simplicity, the examples in this guide check the
error status and call a separate function, handle_err(), to handle any
errors. One possible definition of handle_err() can be found within the
documentation of nc_strerror (@pxref{nc_strerror}).

The nc_strerror function is available to convert a returned integer
error status into an error message string.

Occasionally, low-level I/O errors may occur in a layer below the
netCDF library. For example, if a write operation causes you to exceed
disk quotas or to attempt to write to a device that is no longer
available, you may get an error from a layer below the netCDF library,
but the resulting write error will still be reflected in the returned
status value.

@node Compiling,  , Errors, Use of the NetCDF Library
@section Compiling and Linking with the NetCDF Library
@cindex linking to netCDF library
@cindex compiling with netCDF library

Details of how to compile and link a program that uses the netCDF C or
FORTRAN interfaces differ, depending on the operating system, the
available compilers, where the netCDF library and include files
are installed, and whether or not you are using shared libraries.
Nevertheless, we provide here examples of how to
compile and link a program that uses the netCDF library on a Unix
platform, so that you can adjust these examples to fit your
installation.

Every C file that references netCDF functions or constants must
contain an appropriate #include statement before the first such
reference:

@example
#include <netcdf.h>
@end example

Unless the netcdf.h file is installed in a standard directory where
the C compiler always looks, you must use the -I option when invoking
the compiler, to specify a directory where netcdf.h is installed, for
example:

@example
cc -c -I/usr/local/netcdf/include myprogram.c
@end example

Alternatively, you could specify an absolute path name in the #include
statement, but then your program would not compile on another platform
where netCDF is installed in a different location.

Unless the netCDF library is installed in a standard directory where
the linker always looks, you must use the -L and -l options to link an
object file that uses the netCDF library.

If the netCDF library was configured with the --enable-shared
flag, and the operating system supports shared libraries, then it
should be possible to link an application program using a relatively
simple command. For example:

@example
cc -o myprogram myprogram.o -L/usr/local/netcdf/lib -lnetcdf
@end example

It should be noted that on some operating systems, when using
shared libraries, the application itself may need to be compiled
using some form of PIC (position independent code)
flag; the particular flag will depend
on the C compiler used. You should try it first without
any PIC flag, and if that fails, then check with the
system administrator about the proper form of PIC flag to use.

In addition, for some C compilers (e.g. Sun's cc compiler)
it is necessary to specify runtime paths to the relevant libnetcdf.so.
This can be accomplished in one of two ways.
@enumerate
@item
Add the path to the directory containing libnetcdf.so
to the LD_LIBRARY_PATH environment variable.
This path is searched at runtime to locate any needed shared library.
This might be accomplished, for example, by the following shell command
(assuming that libnetcdf.so is in /usr/local/netcdf/lib).
@example
LD_LIBRARY_PATH="/usr/local/netcdf/lib:$LD_LIBRARY_PATH"
export LD_LIBRARY_PATH
@end example

@item
Set the so-called runtime path when the application is linked
so that the absolute paths of all needed shared libraries is
included in the application binary.
For gcc under Linus, this is usually automatic.
For C compilers on Solaris (and probably other operating systems)
the runtime path must be specified at
link time. The command in this case might look like this.
@example
cc -o myprogram myprogram.o -L/usr/local/netcdf/lib -lnetcdf -R/usr/local/netcdf/lib
@end example
Note that the -R flag is also C compiler dependent.
For gcc and Linux, for example, the specification is usually of this form.
@example
cc ...  -Wl,-rpath,/usr/local/netcdf/lib
@end example
Other compilers may use other flags to specify this. Check
with the local system administrator.
@end enumerate

If shared libraries are not supported or are not being used for some
reason, then it is necessary to include all the dependent libraries in
the compile command.  For example, for a netCDF-4 enabled library, it
will be necessary to link with two HDF5 libraries,
at least one compression library, and
(on some systems) the math library.
@example
cc -o myprogram myprogram.o -L/usr/local/netcdf/lib -L/usr/local/hdf5/lib -lnetcdf -lhdf5_hl -lhdf5 -lz
@end example

Other configuration features (e.g. DAP support or parallel IO)
may require additional libraries.

A complete list of necessary libraries can be obtained by
executing the ``nc-config --libs'' command.
For example:
@example
./nc-config --libs
@end example
might return something like this:
@example
-L/tmp/install/spock/lib -lnetcdf -L/upc/share/stdinstall/local/spock/lib
-lhdf5_hl -lhdf5 -L/upc/share/stdinstall/local/spock/lib -lz -lm
-L/upc/share/stdinstall/local/spock/lib -lcurl -L/usr/kerberos/lib64
-L/upc/share/stdinstall/local/spock/lib
-lidn -lssl -lcrypto -lldap -lrt -lssl -lcrypto -ldl -lz -lz
@end example

Obviously there is some redundancy in this list, so it can be reduced
somewhat to produce this slightly simpler list.
@example
-L/tmp/install/spock/lib -lnetcdf
-L/upc/share/stdinstall/local/spock/lib -lhdf5 -lhdf5_hl -lz -lcurl
-L/usr/kerberos/lib64 -lcrypto -lssl
-ldl -lidn -lldap -lm -lrt 
@end example

@node Datasets, Groups, Use of the NetCDF Library, Top
@chapter Datasets
@cindex datasets, overview

This chapter presents the interfaces of the netCDF functions that deal
with a netCDF dataset or the whole netCDF library.

A netCDF dataset that has not yet been opened can only be referred to
by its dataset name. Once a netCDF dataset is opened, it is referred
to by a netCDF ID, which is a small non-negative integer returned when
you create or open the dataset. A netCDF ID is much like a file
descriptor in C or a logical unit number in FORTRAN. In any single
program, the netCDF IDs of distinct open netCDF datasets are
distinct. A single netCDF dataset may be opened multiple times and
will then have multiple distinct netCDF IDs; however at most one of
the open instances of a single netCDF dataset should permit
writing. When an open netCDF dataset is closed, the ID is no longer
associated with a netCDF dataset.

Functions that deal with the netCDF library include:
@itemize

@item
Get version of library. 

@item
Get error message corresponding to a returned error code. 
@end itemize

The operations supported on a netCDF dataset as a single object are:
@itemize

@item
Create, given dataset name and whether to overwrite or not. 

@item
Open for access, given dataset name and read or write intent. 

@item
Put into define mode, to add dimensions, variables, or attributes.

@item
Take out of define mode, checking consistency of additions. 

@item
Close, writing to disk if required. 

@item
Inquire about the number of dimensions, number of variables, number of
global attributes, and ID of the unlimited dimension, if any.

@item
Synchronize to disk to make sure it is current. 

@item
Set and unset nofill mode for optimized sequential writes. 

@item
After a summary of conventions used in describing the netCDF
interfaces, the rest of this chapter presents a detailed description
of the interfaces for these operations.
@end itemize

@menu
* Interface Descriptions::      What's in the Function Documentation
* parallel access::             
* nc_strerror::                 Get Error Messages
* nc_inq_libvers::              Get netCDF library version
* nc_create::                   Create a Dataset
* nc__create::                  Create a Dataset with Performance Tuning
* nc_create_par::               
* nc_open::                     Open a Dataset
* nc__open::                    Open a Dataset with Performance Tuning
* nc_open_par::                 
* nc_redef::                    Put a Dataset into Define Mode
* nc_enddef::                   Leave Define Mode
* nc__enddef::                  Leave Define Mode with Performance Tuning
* nc_close::                    Close a Dataset
* nc_inq Family::               Inquire about a Dataset
* nc_sync::                     Synchronize a Dataset to Disk
* nc_abort::                    Back Out of Recent Definitions
* nc_set_fill::                 Set Fill Mode for Writes
* nc_set_default_format::       Change the default output format
* nc_set_chunk_cache::          
* nc_get_chunk_cache::          
@end menu

@node Interface Descriptions, parallel access, Datasets, Datasets
@section NetCDF Library Interface Descriptions
@cindex interface descriptions

Each interface description for a particular netCDF function in this
and later chapters contains:

@itemize

@item
a description of the purpose of the function; 

@item
a C function prototype that presents the type and order of the formal
parameters to the function;

@item
a description of each formal parameter in the C interface; 

@item
a list of possible error conditions; and 

@item
an example of a C program fragment calling the netCDF function (and
perhaps other netCDF functions).
@end itemize

The examples follow a simple convention for error handling, always
checking the error status returned from each netCDF function call and
calling a handle_error function in case an error was detected. For an
example of such a function, see @ref{nc_strerror}.

@node parallel access, nc_strerror, Interface Descriptions, Datasets
@section Parallel Access for NetCDF Files
@cindex parallel access
@cindex parallel example

To use parallel access, open or create the file with nc_open_par
(see @ref{nc_open_par}) or nc_create_par (see @ref{nc_create_par}). 

The mode flag NC_PNETCDF will be automatically turned on for classic
or 64-bit offset files opened or created with the parallel access
functions.

The following example shows the creation of a file using parallel
access with a netCDF-4/HDF5 file, and how a program might write data
to such a file.

@example
#include "netcdf.h"
#include <mpi.h>
#include <assert.h>
#include "hdf5.h"
#include <string.h>
#include <stdlib.h>

#define BAIL(e) do @{ \
printf("Bailing out in file %s, line %d, error:%s.\n", __FILE__, __LINE__, nc_strerror(e)); \
return e; \
@} while (0) 

#define FILE "test_par.nc"
#define NDIMS 2
#define DIMSIZE 24
#define QTR_DATA (DIMSIZE*DIMSIZE/4)
#define NUM_PROC 4

int
main(int argc, char **argv)
@{
    /* MPI stuff. */
    int mpi_namelen;            
    char mpi_name[MPI_MAX_PROCESSOR_NAME];
    int mpi_size, mpi_rank;
    MPI_Comm comm = MPI_COMM_WORLD;
    MPI_Info info = MPI_INFO_NULL;

    /* Netcdf-4 stuff. */
    int ncid, v1id, dimids[NDIMS];
    size_t start[NDIMS], count[NDIMS];

    int data[DIMSIZE*DIMSIZE], j, i, res;

    /* Initialize MPI. */
    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD, &mpi_size);
    MPI_Comm_rank(MPI_COMM_WORLD, &mpi_rank);
    MPI_Get_processor_name(mpi_name, &mpi_namelen);
    printf("mpi_name: %s size: %d rank: %d\n", mpi_name, 
           mpi_size, mpi_rank);

    /* Create a parallel netcdf-4 file. */
    if ((res = nc_create_par(FILE, NC_NETCDF4|NC_MPIIO, comm, 
                             info, &ncid)))
        BAIL(res);

    /* Create two dimensions. */
    if ((res = nc_def_dim(ncid, "d1", DIMSIZE, dimids)))
       BAIL(res);
    if ((res = nc_def_dim(ncid, "d2", DIMSIZE, &dimids[1])))
       BAIL(res);

    /* Create one var. */
    if ((res = nc_def_var(ncid, "v1", NC_INT, NDIMS, dimids, &v1id)))
       BAIL(res);

    if ((res = nc_enddef(ncid)))
       BAIL(res);

    /* Set up slab for this process. */
    start[0] = mpi_rank * DIMSIZE/mpi_size;
    start[1] = 0;
    count[0] = DIMSIZE/mpi_size;
    count[1] = DIMSIZE;
    printf("mpi_rank=%d start[0]=%d start[1]=%d count[0]=%d count[1]=%d\n",
           mpi_rank, start[0], start[1], count[0], count[1]);

    /* Create phony data. We're going to write a 24x24 array of ints,
       in 4 sets of 144. */
    printf("mpi_rank*QTR_DATA=%d (mpi_rank+1)*QTR_DATA-1=%d\n",
           mpi_rank*QTR_DATA, (mpi_rank+1)*QTR_DATA);
    for (i=mpi_rank*QTR_DATA; i<(mpi_rank+1)*QTR_DATA; i++)
       data[i] = mpi_rank;

    /*if ((res = nc_var_par_access(ncid, v1id, NC_COLLECTIVE)))
      BAIL(res);*/
    if ((res = nc_var_par_access(ncid, v1id, NC_INDEPENDENT)))
       BAIL(res);

    /* Write slabs of phony data. */
    if ((res = nc_put_vara_int(ncid, v1id, start, count, 
                               &data[mpi_rank*QTR_DATA])))
       BAIL(res);

    /* Close the netcdf file. */
    if ((res = nc_close(ncid)))
        BAIL(res);
    
    /* Shut down MPI. */
    MPI_Finalize();

    return 0;
@}

@end example

@node nc_strerror, nc_inq_libvers, parallel access, Datasets
@section Get error message corresponding to error status: nc_strerror 
@findex nc_strerror
@findex handle_err
@cindex error codes
@cindex nc_strerror, example

The function nc_strerror returns a static reference to an error
message string corresponding to an integer netCDF error status or to a
system error number, presumably returned by a previous call to some
other netCDF function. The list of netCDF error status codes is
available in the appropriate include file for each language binding.

@heading Usage 
@example
const char * nc_strerror(int ncerr);
@end example

@table @code
@item ncerr
An error status that might have been returned from a previous call to
some netCDF function.
@end table

@heading Errors

If you provide an invalid integer error status that does not
correspond to any netCDF error message or or to any system error
message (as understood by the system strerror function), nc_strerror
returns a string indicating that there is no such error status.

@heading Example 

Here is an example of a simple error handling function that uses
nc_strerror to print the error message corresponding to the netCDF
error status returned from any netCDF function call and then exit:

@example
#include <netcdf.h>
   ... 
void handle_error(int status) @{
if (status != NC_NOERR) @{
   fprintf(stderr, "%s\n", nc_strerror(status));
   exit(-1);
   @}
@}
@end example

@node nc_inq_libvers, nc_create, nc_strerror, Datasets
@section Get netCDF library version: nc_inq_libvers
@findex nc_inq_libvers
@cindex version of netCDF, discovering
@cindex netCDF library version
@cindex nc_inq_libvers, example

The function nc_inq_libvers returns a string identifying the version
of the netCDF library, and when it was built.

@heading Usage 
@example
const char * nc_inq_libvers(void);
@end example

@heading Errors 

This function takes no arguments, and thus no errors are possible in
its invocation.

@heading Example 

Here is an example using nc_inq_libvers to print the version of the
netCDF library with which the program is linked:

@example
#include <netcdf.h>
   ... 
   printf("%s\n", nc_inq_libvers());
@end example

@node nc_create, nc__create, nc_inq_libvers, Datasets
@section Create a NetCDF Dataset: nc_create 
@findex nc_create
@cindex nc_create, example
@cindex nc_create, flags
@vindex NC_NOCLOBBER
@vindex NC_CLOBBER
@vindex NC_SHARE
@vindex NC_64BIT_OFFSET
@cindex HDF5 errors, first create

This function creates a new netCDF dataset, returning a netCDF ID that
can subsequently be used to refer to the netCDF dataset in other
netCDF function calls. The new netCDF dataset opened for write access
and placed in define mode, ready for you to add dimensions, variables,
and attributes.

A creation mode flag specifies:

@itemize

@item
whether to overwrite any existing dataset with the same name,
@item
whether access to the dataset is shared,
@item
whether this file should be in netCDF classic format (the default), 
the new 64-bit offset format (use NC_64BIT_OFFSET), or NC_NETCDF4 for
a netCDF-4/HDF5 file.
@end itemize

@heading Usage 

NOTE: When creating a netCDF-4 file HDF5 error reporting is turned
off, if it is on. This doesn't stop the HDF5 error stack from
recording the errors, it simply stops their display to the user
through stderr.

@example
int nc_create (const char* path, int cmode, int *ncidp);
@end example

@table @code
@item path
The file name of the new netCDF dataset.
 
@item cmode
The creation mode flag. The following flags are available:
NC_NOCLOBBER, NC_SHARE, NC_64BIT_OFFSET, NC_NETCDF4, NC_CLASSIC_MODEL.

Setting NC_NOCLOBBER means you do not want to clobber (overwrite) an
existing dataset; an error (NC_EEXIST) is returned if the specified
dataset already exists.

The NC_SHARE flag is appropriate when one process may be writing the
dataset and one or more other processes reading the dataset
concurrently; it means that dataset accesses are not buffered and
caching is limited. Since the buffering scheme is optimized for
sequential access, programs that do not access data sequentially may
see some performance improvement by setting the NC_SHARE flag. This
flag is ignored for netCDF-4 files. (See below.)

Setting NC_64BIT_OFFSET causes netCDF to create a 64-bit offset format
file, instead of a netCDF classic format file. The 64-bit offset
format imposes far fewer restrictions on very large (i.e. over 2 GB)
data files. @xref{Large File Support,,, netcdf, @value{n-man}}.

A zero value (defined for convenience as NC_CLOBBER) specifies the
default behavior: overwrite any existing dataset with the same file
name and buffer and cache accesses for efficiency. The dataset will be
in netCDF classic format. @xref{NetCDF Classic Format Limitations,,,
netcdf, @value{n-man}}.

Setting NC_NETCDF4 causes netCDF to create a HDF5/NetCDF-4 file.

Setting NC_CLASSIC_MODEL causes netCDF to enforce the classic data
model in this file. (This only has effect for netCDF-4/HDF5 files, as
classic and 64-bit offset files always use the classic model.) When
used with NC_NETCDF4, this flag ensures that the resulting
netCDF-4/HDF5 file may never contain any new constructs from the
enhanced data model. That is, it cannot contain groups, user defined
types, multiple unlimited dimensions, or new atomic types. The
advantage of this restriction is that such files are guaranteed to
work with existing netCDF software.

@item ncidp
Pointer to location where returned netCDF ID is to be stored.
@end table

@heading Errors 
nc_create returns the value NC_NOERR if no errors occurred. Possible
causes of errors include:
@itemize

@item
Passing a dataset name that includes a directory that does not exist.
@item
Specifying a dataset name of a file that exists and also specifying
NC_NOCLOBBER.
@item
Specifying a meaningless value for the creation mode.
@item
Attempting to create a netCDF dataset in a directory where you don't
have permission to create files.
@end itemize

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item NC_ENOMEM
System out of memory.

@item NC_EHDFERR
HDF5 error (netCDF-4 files only).

@item NC_EFILEMETA
Error writing netCDF-4 file-level metadata in HDF5 file. (netCDF-4
files only).

@end table

@heading Examples

In this example we create a netCDF dataset named foo.nc; we want the
dataset to be created in the current directory only if a dataset with
that name does not already exist:

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
   ... 
status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
if (status != NC_NOERR) handle_error(status);
@end example

In this example we create a netCDF dataset named foo_large.nc. It will
be in the 64-bit offset format.

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
   ... 
status = nc_create("foo_large.nc", NC_NOCLOBBER|NC_64BIT_OFFSET, &ncid);
if (status != NC_NOERR) handle_error(status);
@end example

In this example we create a netCDF dataset named foo_HDF5.nc. It will
be in the HDF5 format.

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
   ... 
status = nc_create("foo_HDF5.nc", NC_NOCLOBBER|NC_NETCDF4, &ncid);
if (status != NC_NOERR) handle_error(status);
@end example

In this example we create a netCDF dataset named
foo_HDF5_classic.nc. It will be in the HDF5 format, but will not allow
the use of any netCDF-4 advanced features. That is, it will conform to
the classic netCDF-3 data model.

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
   ... 
status = nc_create("foo_HDF5_classic.nc", NC_NOCLOBBER|NC_NETCDF4|NC_CLASSIC_MODEL, &ncid);
if (status != NC_NOERR) handle_error(status);
@end example

A variant of nc_create, nc__create (note the double underscore) allows
users to specify two tuning parameters for the file that it is
creating. These tuning parameters are not written to the data file,
they are only used for so long as the file remains open after an
nc__create. @xref{nc__create}.

@node nc__create, nc_create_par, nc_create, Datasets
@section Create a NetCDF Dataset With Performance Options: nc__create 
@findex nc__create
@cindex nc__create, example
@cindex nc__create, flags
@vindex NC_NOCLOBBER
@vindex NC_CLOBBER
@vindex NC_SHARE
@vindex NC_64BIT_OFFSET

This function is a variant of nc_create, nc__create (note the double
underscore) allows users to specify two tuning parameters for the
file that it is creating. These tuning parameters are not written to
the data file, they are only used for so long as the file remains open
after an nc__create.

This function creates a new netCDF dataset, returning a netCDF ID that
can subsequently be used to refer to the netCDF dataset in other
netCDF function calls. The new netCDF dataset opened for write access
and placed in define mode, ready for you to add dimensions, variables,
and attributes.

A creation mode flag specifies whether to overwrite any existing
dataset with the same name and whether access to the dataset is
shared, and whether this file should be in netCDF classic format (the
default), or the new 64-bit offset format.

@heading Usage 

@example
int nc__create(const char *path, int cmode, size_t initialsz,
               size_t *bufrsizehintp, int *ncidp);
@end example

@table @code
@item path
The file name of the new netCDF dataset.
 
@item cmode
The creation mode flag. The following flags are available:
NC_NOCLOBBER, NC_SHARE, and NC_64BIT_OFFSET, NC_NETCDF4, NC_CLASSIC_MODEL.

Setting NC_NOCLOBBER means you do not want to clobber (overwrite) an
existing dataset; an error (NC_EEXIST) is returned if the specified
dataset already exists.

The NC_SHARE flag is appropriate when one process may be writing the
dataset and one or more other processes reading the dataset
concurrently; it means that dataset accesses are not buffered and
caching is limited. Since the buffering scheme is optimized for
sequential access, programs that do not access data sequentially may
see some performance improvement by setting the NC_SHARE flag.  This
flag is ignored for netCDF-4 files. (See below.)

Setting NC_64BIT_OFFSET causes netCDF to create a 64-bit offset format
file, instead of a netCDF classic format file. The 64-bit offset
format imposes far fewer restrictions on very large (i.e. over 2 GB)
data files. @xref{Large File Support,,, netcdf, @value{n-man}}.

A zero value (defined for convenience as NC_CLOBBER) specifies the
default behavior: overwrite any existing dataset with the same file
name and buffer and cache accesses for efficiency. The dataset will be
in netCDF classic format. @xref{NetCDF Classic Format Limitations,,,
netcdf, @value{n-man}}.

Setting NC_NETCDF4 causes netCDF to create a HDF5/NetCDF-4 file.

Setting NC_CLASSIC_MODEL causes netCDF to enforce the classic data
model in this file. (This only has effect for netCDF-4/HDF5 files, as
classic and 64-bit offset files always use the classic model.) When
used with NC_NETCDF4, this flag ensures that the resulting
netCDF-4/HDF5 file may never contain any new constructs from the
enhanced data model. That is, it cannot contain groups, user defined
types, multiple unlimited dimensions, or new atomic types. The
advantage of this restriction is that such files are guaranteed to
work with existing netCDF software.

@item initialsz
On some systems, and with custom I/O layers, it may be advantageous to
set the size of the output file at creation time. This parameter sets
the initial size of the file at creation time.

@item bufrsizehintp
The argument referenced by bufrsizehintp controls a space versus time
tradeoff, memory allocated in the netcdf library versus number of system
calls.

Because of internal requirements, the value may not be set to exactly
the value requested. The actual value chosen is returned by reference.

Using the value NC_SIZEHINT_DEFAULT causes the library to choose a
default. How the system chooses the default depends on the system. On
many systems, the "preferred I/O block size" is available from the
stat() system call, struct stat member st_blksize. If this is
available it is used. Lacking that, twice the system pagesize is used.

Lacking a call to discover the system pagesize, we just set default
bufrsize to 8192.

The bufrsize is a property of a given open netcdf descriptor
ncid, it is not a persistent property of the netcdf dataset.

@item ncidp
Pointer to location where returned netCDF ID is to be stored.
@end table

@heading Errors 
nc_create returns the value NC_NOERR if no errors occurred. Possible
causes of errors include:
@itemize

@item
Passing a dataset name that includes a directory that does not exist.
@item
Specifying a dataset name of a file that exists and also specifying
NC_NOCLOBBER.
@item
Specifying a meaningless value for the creation mode.
@item
Attempting to create a netCDF dataset in a directory where you don't
have permission to create files.
@end itemize

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item NC_ENOMEM
System out of memory.

@item NC_EHDFERR
HDF5 error (netCDF-4 files only).

@item NC_EFILEMETA
Error writing netCDF-4 file-level metadata in HDF5 file. (netCDF-4
files only).

@end table

@heading Examples

In this example we create a netCDF dataset named foo.nc; we want the
dataset to be created in the current directory only if a dataset with
that name does not already exist:

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
   ... 
status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
if (status != NC_NOERR) handle_error(status);
@end example

In this example we create a netCDF dataset named foo_large.nc; we want the
dataset to be created in the current directory only if a dataset with
that name does not already exist. We also specify that bufrsize and
initial size for the file.

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
int intialsz = 2048;
int *bufrsize;
   ... 
*bufrsize = 1024;
status = nc__create("foo.nc", NC_NOCLOBBER, initialsz, bufrsize, &ncid);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_create_par, nc_open, nc__create, Datasets
@section Create a NetCDF Dataset With Performance Options: nc_create_par 
@findex nc_create_par
@cindex nc_create_par, example
@cindex nc_create_par, flags
@vindex NC_NOCLOBBER
@vindex NC_CLOBBER
@vindex NC_MPIIO
@vindex NC_MPIPOSIX

This function is a variant of nc_create, nc_create_par allows users to
open a file on a MPI/IO or MPI/Posix parallel file system. 

The parallel parameters are not written to the data file, they are
only used for so long as the file remains open after an nc_create_par.

This function creates a new netCDF dataset, returning a netCDF ID that
can subsequently be used to refer to the netCDF dataset in other
netCDF function calls. The new netCDF dataset opened for write access
and placed in define mode, ready for you to add dimensions, variables,
and attributes.

If the NC_NETCDF4 flag is used, the HDF5 library is used for parallel
I/O. If not, the parallel-netcdf library is used.

When a file is created for parallel access, independent operations are
the default. To use independent access on a variable,
@xref{nc_var_par_access}.

@heading Usage 

@example
int nc_create_par(const char *path, int cmode, MPI_Comm comm,
                  MPI_Info info, int ncidp);
@end example

@table @code
@item path
The file name of the new netCDF dataset.
 
@item cmode
Either the NC_MPIIO or NC_MPIPOSIX flags may be present if the
NC_NETCDF4 flag is used.

The NC_SHARE flag is ignored.

@item comm
The MPI_Comm object returned by the MPI layer.

@item info
The MPI_Info object returned by the MPI layer, if MPI/IO
is being used, or 0 if MPI/Posix is being used.

@item ncidp
Pointer to location where returned netCDF ID is to be stored.

@end table

@heading Return Codes 

@table @code

@item NC_NOERR
No error.

@item NC_EPARINIT
Could not initialize parallel access at the HDF5 layer.

@item NC_EFILEMETA
HDF5 layer cannot handle create or root group open.

@item NC_EEXIST
Specifying a dataset name of a file that exists and also specifying
NC_NOCLOBBER.

@item NC_EINVAL
Bad value for the creation mode.

@item NC_EHDFERR
Unexpected error from the HDF5 layer.

@end table

@heading Examples

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
   ... 
*bufrsize = 1024;
status = nc__create("foo.nc", NC_NOCLOBBER, initialsz, bufrsize, &ncid);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_open, nc__open, nc_create_par, Datasets
@section Open a NetCDF Dataset for Access: nc_open 
@findex nc_open
@cindex nc_open, example
@vindex NC_NOWRITE
@vindex NC_WRITE
@vindex NC_SHARE, in nc_open
@cindex HDF5 errors, first create

The function nc_open opens an existing netCDF dataset for access. It
determines the underlying file format automatically. Use the same call
to open a netCDF classic, 64-bit offset, or netCDF-4 file.

@heading Usage 

@example
int nc_open (const char *path, int omode, int *ncidp);
@end example

@table @code

@item path
File name for netCDF dataset to be opened.
When DAP support is enabled, then the path may be an OPeNDAP
URL rather than a file path.
 
@item omode
A zero value (or NC_NOWRITE) specifies the default behavior: open the
dataset with read-only access, buffering and caching accesses for
efficiency

Otherwise, the open mode is NC_WRITE, NC_SHARE, or
NC_WRITE|NC_SHARE. Setting the NC_WRITE flag opens the dataset with
read-write access. ("Writing" means any kind of change to the dataset,
including appending or changing data, adding or renaming dimensions,
variables, and attributes, or deleting attributes.) 

The NC_SHARE flag is only used for netCDF classic and 64-bit offset
files. It is appropriate when one process may be writing the
dataset and one or more other processes reading the dataset
concurrently; it means that dataset accesses are not buffered and
caching is limited. Since the buffering scheme is optimized for
sequential access, programs that do not access data sequentially may
see some performance improvement by setting the NC_SHARE flag.

It is not necessary to pass any information about the format of the
file being opened. The file type will be detected automatically by the
netCDF library.
 
If a the path is a DAP URL, then the open mode is read-only.
Setting NC_WRITE will be ignored.

@item ncidp
Pointer to location where returned netCDF ID is to be stored.
@end table

@heading Errors 

When opening a netCDF-4 file HDF5 error reporting is turned off, if
it is on. This doesn't stop the HDF5 error stack from recording the
errors, it simply stops their display to the user through stderr.

nc_open returns the value NC_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
The specified netCDF dataset does not exist. 
@item
A meaningless mode was specified. 
@end itemize

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item NC_NOMEM
Out of memory.

@item NC_EHDFERR
HDF5 error. (NetCDF-4 files only.)

@item NC_EDIMMETA
Error in netCDF-4 dimension metadata. (NetCDF-4 files only.)

@item NC_ENOCOMPOIND
(NetCDF-4 files only.)

@end table

@heading Example 

Here is an example using nc_open to open an existing netCDF dataset
named foo.nc for read-only, non-shared access:

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
   ... 
status = nc_open("foo.nc", 0, &ncid);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc__open, nc_open_par, nc_open, Datasets
@section Open a NetCDF Dataset for Access with Performance Tuning: nc__open 
@findex nc__open
@cindex nc__open, example
@vindex NC_NOWRITE
@vindex NC_WRITE
@vindex NC_SHARE, in nc__open

A function opens a netCDF dataset for access with an additional
performance tuning parameter.
When DAP support is enabled, it is possible to open a DAP data source
through this interface, but it is deprecated because
all of the performance tuning parameters are ignored.
The standard nc_open interface should be used instead.

@heading Usage 

@example
int nc__open(const char *path, int mode, size_t *bufrsizehintp, int *ncidp);
@end example

@table @code

@item path
File name for netCDF dataset to be opened.
 
@item omode
A zero value (or NC_NOWRITE) specifies the default behavior: open the
dataset with read-only access, buffering and caching accesses for
efficiency

Otherwise, the open mode is NC_WRITE, NC_SHARE, or
NC_WRITE|NC_SHARE. Setting the NC_WRITE flag opens the dataset with
read-write access. ("Writing" means any kind of change to the dataset,
including appending or changing data, adding or renaming dimensions,
variables, and attributes, or deleting attributes.) The NC_SHARE flag
is appropriate when one process may be writing the dataset and one or
more other processes reading the dataset concurrently; it means that
dataset accesses are not buffered and caching is limited. Since the
buffering scheme is optimized for sequential access, programs that do
not access data sequentially may see some performance improvement by
setting the NC_SHARE flag.
 
@item bufrsizehintp
The argument referenced by bufrsizehintp controls a space versus time
tradeoff, memory allocated in the netcdf library versus number of system
calls.

Because of internal requirements, the value may not be set to exactly
the value requested. The actual value chosen is returned by reference.

Using the value NC_SIZEHINT_DEFAULT causes the library to choose a
default. How the system chooses the default depends on the system. On
many systems, the "preferred I/O block size" is available from the
stat() system call, struct stat member st_blksize. If this is
available it is used. Lacking that, twice the system pagesize is used.

Lacking a call to discover the system pagesize, we just set default
bufrsize to 8192.

The bufrsize is a property of a given open netcdf descriptor
ncid, it is not a persistent property of the netcdf dataset.

@item ncidp
Pointer to location where returned netCDF ID is to be stored.
@end table

@heading Errors 

nc__open returns the value NC_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
The specified netCDF dataset does not exist. 
@item
A meaningless mode was specified. 
@end itemize

@heading Example 
Here is an example using nc__open to open an existing netCDF dataset
named foo.nc for read-only, non-shared access:

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
size_t bufrsize;
   ... 
*bufrsize = 1024;
status = nc_open("foo.nc", 0, &bufrsize, &ncid);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_open_par, nc_redef, nc__open, Datasets
@section Open a NetCDF Dataset for Parallel Access
@findex nc_open_par
@vindex NC_NOWRITE
@vindex NC_WRITE
@vindex NC_NETCDF4

This function opens a netCDF-4 dataset for parallel access. 

For netcdf-4/HDF5 files, the HDF5 library parallel I/O is used. This
opens the file using either MPI-IO or MPI-POSIX. 

DAP access is not allowed with parallel I/O.

When netCDF opens a file for parallel access, independent operations
are the default. To use independent access on a variable,
@xref{nc_var_par_access}.

@heading Usage 

@example
int nc_open_par(const char *path, int mode, MPI_Comm comm, 
                MPI_Info info, int *ncidp);
@end example

@table @code

@item path
File name for netCDF dataset to be opened.
 
@item omode
Either the NC_MPIIO or NC_MPIPOSIX flags may be present for a
netCDF-4/HDF5 file.

The flag NC_WRITE opens the dataset with read-write access. ("Writing"
means any kind of change to the dataset, including appending or
changing data, adding or renaming dimensions, variables, and
attributes, or deleting attributes.)

All other flags are ignored or not allowed. The NC_NETCDF4 flag is not
required, as the file type is detected when the file is opened.
 
@item comm
MPI_Comm object returned by the MPI layer.

@item info
MPI_Info object returned by the MPI layer, or NULL if MPI-POSIX access
is desired.

@item ncidp
Pointer to location where returned netCDF ID is to be stored.

@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item
The specified netCDF dataset does not exist. 

@item
A meaningless mode was specified. 

@end table

@heading Example 
Here is an example (from nc_test4/tst_parallel2.c) using nc_open_par.

@example
    /* Reopen the file and check it. */
    if (nc_open_par(file_name, NC_NOWRITE, comm, info, &ncid)) ERR;

    /* Read all the slabs this process is responsible for. */
    for (i = 0; i < NUM_SLABS / mpi_size; i++)
    @{
       start[0] = NUM_SLABS / mpi_size * mpi_rank + i;
       /* Read one slab of data. */
       if (nc_get_vara_int(ncid, varid, start, count, data_in)) ERR;
    @}
@end example

@node nc_redef, nc_enddef, nc_open_par, Datasets
@section Put Open NetCDF Dataset into Define Mode: nc_redef 
@findex nc_redef
@cindex nc_redef, example
@cindex adding dimensions using nc_redef
@cindex adding variables using nc_redef
@cindex adding attributes using nc_redef

The function nc_redef puts an open netCDF dataset into define mode, so
dimensions, variables, and attributes can be added or renamed and
attributes can be deleted.

@heading Usage 

For netCDF-4 files (i.e. files created with NC_NETCDF4 in the cmode,
@pxref{nc_create}), it is not necessary to call nc_redef unless the
file was also created with NC_STRICT_NC3. For straight-up netCDF-4
files, nc_redef is called automatically, as needed.

For all netCDF-4 files, the root ncid must be used. This is the ncid
returned by nc_open and nc_create, and points to the root of the
hierarchy tree for netCDF-4 files.

@example
int nc_redef(int ncid);
@end example

@table @code
@item ncid
netCDF ID, from a previous call to nc_open or nc_create.
@end table

@heading Errors 
nc_redef returns the value NC_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
The specified netCDF dataset is already in define mode. This error
code will only be returned for classic and 64-bit offset format files.

@item
The specified netCDF dataset was opened for read-only. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Errors 

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad ncid.

@item NC_EBADGRPID
The ncid must refer to the root group of the file, that is, the group
returned by nc_open or nc_create. (@pxref{nc_open} @pxref{nc_create}).

@item NC_EINDEFINE
Already in define mode.

@item NC_EPERM
File is read-only.

@end table

@heading Example 

Here is an example using nc_redef to open an existing netCDF dataset
named foo.nc and put it into define mode:

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);  /* open dataset */
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_redef(ncid);                      /* put in define mode */
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_enddef, nc__enddef, nc_redef, Datasets
@section Leave Define Mode: nc_enddef 
@findex nc_enddef
@cindex nc_enddef, example

The function nc_enddef takes an open netCDF dataset out of define
mode. The changes made to the netCDF dataset while it was in define
mode are checked and committed to disk if no problems
occurred. Non-record variables may be initialized to a "fill value" as
well. @xref{nc_set_fill}. The netCDF dataset is then placed in data
mode, so variable data can be read or written.

It's not necessary to call nc_enddef for netCDF-4 files. With netCDF-4
files, nc_enddef is called when needed by the netcdf-4 library. User
calls to nc_enddef for netCDF-4 files still flush the metadata to
disk.

This call may involve copying data under some circumstances. For a
more extensive discussion see @ref{File Structure and Performance,,,
netcdf, @value{n-man}}.

For netCDF-4/HDF5 format files there are some variable settings (the
compression, endianness, fletcher32 error correction, and fill value)
which must be set (if they are going to be set at all) between the
nc_def_var and the next nc_enddef. Once the nc_enddef is called, these
settings can no longer be changed for a variable.

@heading Usage 

@example
int nc_enddef(int ncid);
@end example

@table @code
@item ncid
NetCDF ID, from a previous call to nc_open or nc_create. If you use a
group id, the enddef will apply to the entire file. That all, the
enddef will not just end define mode in one group, but in the entire file.
@end table

@heading Errors 

nc_enddef returns the value NC_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
The specified netCDF dataset is not in define mode. 

@item
The specified netCDF ID does not refer to an open netCDF dataset.

@item
The size of one or more variables exceed the size constraints for
whichever variant of the file format is in use).
@xref{Large File Support,,, netcdf, @value{n-man}}.
@end itemize

@heading Example 

Here is an example using nc_enddef to finish the definitions of a new
netCDF dataset named foo.nc and put it into data mode:

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
   ... 
status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
if (status != NC_NOERR) handle_error(status);

   ...       /* create dimensions, variables, attributes */

status = nc_enddef(ncid);  /*leave define mode*/
if (status != NC_NOERR) handle_error(status);
@end example

@node nc__enddef, nc_close, nc_enddef, Datasets
@section Leave Define Mode with Performance Tuning: nc__enddef 
@findex nc__enddef
@cindex nc__enddef, example

The function nc__enddef takes an open netCDF dataset out of define
mode. The changes made to the netCDF dataset while it was in define
mode are checked and committed to disk if no problems
occurred. Non-record variables may be initialized to a "fill value" as
well. @xref{nc_set_fill}. The netCDF dataset is then placed in data
mode, so variable data can be read or written.

This call may involve copying data under some circumstances. For a
more extensive discussion see @ref{File Structure and Performance,,,
netcdf, @value{n-man}}.

Caution: this function exposes internals of the netcdf version 1 file
format. Users should use nc_enddef in most circumstances. This
function may not be available on future netcdf implementations.

The current netcdf file format has three sections, the "header"
section, the data section for fixed size variables, and the data
section for variables which have an unlimited dimension (record
variables).

The header begins at the beginning of the file. The index (offset) of
the beginning of the other two sections is contained in the
header. Typically, there is no space between the sections. This causes
copying overhead to accrue if one wishes to change the size of the
sections, as may happen when changing names of things, text attribute
values, adding attributes or adding variables. Also, for buffered i/o,
there may be advantages to aligning sections in certain ways.

The minfree parameters allow one to control costs of future calls to
nc_redef, nc_enddef by requesting that minfree bytes be available at
the end of the section.

The align parameters allow one to set the alignment of the beginning
of the corresponding sections. The beginning of the section is rounded
up to an index which is a multiple of the align parameter. The flag
value ALIGN_CHUNK tells the library to use the bufrsize (see above)
as the align parameter.  It has nothing to do with the chunking
(multidimensional tiling) features of netCDF-4.

The file format requires mod 4 alignment, so the align parameters
are silently rounded up to multiples of 4. The usual call,

@example
nc_enddef(ncid);
@end example

is equivalent to

@example
nc__enddef(ncid, 0, 4, 0, 4);
@end example

The file format does not contain a "record size" value, this is
calculated from the sizes of the record variables. This unfortunate
fact prevents us from providing minfree and alignment control of the
"records" in a netcdf file. If you add a variable which has an
unlimited dimension, the third section will always be copied with the
new variable added.

@heading Usage 

@example
int nc__enddef(int ncid, size_t h_minfree, size_t v_align,
               size_t v_minfree, size_t r_align);
@end example

@table @code

@item ncid
NetCDF ID, from a previous call to nc_open or nc_create.

@item h_minfree
Sets the pad at the end of the "header" section.

@item v_align
Controls the alignment of the beginning of the data section for fixed
size variables.

@item v_minfree
Sets the pad at the end of the data section for fixed size variables.

@item r_align
Controls the alignment of the beginning of the data section for
variables which have an unlimited dimension (record variables).

@end table

@heading Errors 

nc__enddef returns the value NC_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
The specified netCDF dataset is not in define mode. 

@item
The specified netCDF ID does not refer to an open netCDF dataset.

@item
The size of one or more variables exceed the size constraints for
whichever variant of the file format is in use).
@xref{Large File Support,,, netcdf, @value{n-man}}.
@end itemize

@heading Example 

Here is an example using nc_enddef to finish the definitions of a new
netCDF dataset named foo.nc and put it into data mode:

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
   ... 
status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
if (status != NC_NOERR) handle_error(status);

   ...       /* create dimensions, variables, attributes */

status = nc_enddef(ncid);  /*leave define mode*/
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_close, nc_inq Family, nc__enddef, Datasets
@section Close an Open NetCDF Dataset: nc_close 
@findex nc_close
@cindex nc_close, example
@cindex nc_close, root group

The function nc_close closes an open netCDF dataset. 

If the dataset in define mode, nc_enddef will be called before
closing. (In this case, if nc_enddef returns an error, nc_abort will
automatically be called to restore the dataset to the consistent state
before define mode was last entered.) After an open netCDF dataset is
closed, its netCDF ID may be reassigned to the next netCDF dataset
that is opened or created.


@heading Usage 

For netCDF-4 files, the ncid of the root group must be passed into
nc_close. 

@example
int nc_close(int ncid);
@end example

@table @code
@item ncid
NetCDF ID, from a previous call to nc_open or nc_create.
@end table

@heading Errors 

nc_close returns the value NC_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
Define mode was entered and the automatic call made to nc_enddef
failed.

@item
The specified netCDF ID does not refer to an open netCDF dataset.
@end itemize

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Invalid id passed.

@item NC_EBADGRPID
ncid did not contain the root group id of this file. (NetCDF-4 only).

@end table

@heading Example 

Here is an example using nc_close to finish the definitions of a new
netCDF dataset named foo.nc and release its netCDF ID:

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
   ... 
status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
if (status != NC_NOERR) handle_error(status);

   ...       /* create dimensions, variables, attributes */

status = nc_close(ncid);       /* close netCDF dataset */
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_inq Family, nc_sync, nc_close, Datasets
@section Inquire about an Open NetCDF Dataset: nc_inq Family
@findex nc_inq Family
@findex nc_inq_ndims
@findex nc_inq_nvars
@findex nc_inq_natts
@findex nc_inq_unlimdim
@findex nc_inq_format
@findex nc_inq_path
@cindex attributes, number of
@cindex variables, number of
@cindex dimensions, number of
@cindex format version
@cindex version, format
@cindex path
@cindex file path
@cindex file name
@cindex URL
@cindex nc_inq Family, example

Members of the nc_inq family of functions return information about an
open netCDF dataset, given its netCDF ID. Dataset inquire functions
may be called from either define mode or data mode. The first
function, nc_inq, returns values for the number of dimensions, the
number of variables, the number of global attributes, and the
dimension ID of the dimension defined with unlimited length, if
any. Most of the other functions in the family each return just one of these
items of information.

For C, these functions include nc_inq, nc_inq_ndims, nc_inq_nvars,
nc_inq_natts, and nc_inq_unlimdim.  An additional function,
nc_inq_format, returns the (rarely needed) format version.  Another
function, nc_inq_path, returns the file name or URL with which a
file was opened or created.

No I/O is performed when these functions are called, since the
required information is available in memory for each open netCDF
dataset.

@heading Usage 
@example
int nc_inq          (int ncid, int *ndimsp, int *nvarsp, int *ngattsp,
                     int *unlimdimidp);
int nc_inq_ndims    (int ncid, int *ndimsp);
int nc_inq_nvars    (int ncid, int *nvarsp);
int nc_inq_natts    (int ncid, int *ngattsp);
int nc_inq_unlimdim (int ncid, int *unlimdimidp);
int nc_inq_format   (int ncid, int *formatp);
int nc_inq_path     (int ncid, size_t *pathlenp, char *path);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item ndimsp
Pointer to location for returned number of dimensions defined for this
netCDF dataset.
 
@item nvarsp
Pointer to location for returned number of variables defined for this
netCDF dataset.
 
@item ngattsp
Pointer to location for returned number of global attributes defined
for this netCDF dataset.
 
@item unlimdimidp
Pointer to location for returned ID of the unlimited dimension, if
there is one for this netCDF dataset. If no unlimited length dimension
has been defined, -1 is returned.

@item formatp
Pointer to location for returned format version, one of 
NC_FORMAT_CLASSIC, NC_FORMAT_64BIT, NC_FORMAT_NETCDF4,
NC_FORMAT_NETCDF4_CLASSIC.

@item pathlenp
Pointer to location for returned length of the string specifying the
path with which a file was opened or created.  For data on remote
servers, this is the length of the URL string provided to open a
connection to the data.  If NULL, this argument is ignored.
returned.

@item path
Pointer to string large enough to contain the returned path with which
the specified open netCDF dataset was opened or created.  If NULL,
this argument is ignored.
@end table

@heading Errors 

All members of the nc_inq family return the value NC_NOERR if no
errors occurred. Otherwise, the returned status indicates an
error. Possible causes of errors include:
@itemize

@item
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Example 

Here is an example using nc_inq to find out about a netCDF dataset
named foo.nc:

@example
#include <netcdf.h>
   ... 
int status, ncid, ndims, nvars, ngatts, unlimdimid;
   ... 
status = nc_open("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq(ncid, &ndims, &nvars, &ngatts, &unlimdimid);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_sync, nc_abort, nc_inq Family, Datasets
@section Synchronize an Open NetCDF Dataset to Disk: nc_sync 
@findex nc_sync
@cindex nc_sync, example

The function nc_sync offers a way to synchronize the disk copy of a
netCDF dataset with in-memory buffers. There are two reasons you might
want to synchronize after writes:
@itemize

@item
To minimize data loss in case of abnormal termination, or 

@item
To make data available to other processes for reading immediately
after it is written. But note that a process that already had the
dataset open for reading would not see the number of records increase
when the writing process calls nc_sync; to accomplish this, the
reading process must call nc_sync.
@end itemize

This function is backward-compatible with previous versions of the
netCDF library. The intent was to allow sharing of a netCDF dataset
among multiple readers and one writer, by having the writer call
nc_sync after writing and the readers call nc_sync before each
read. For a writer, this flushes buffers to disk. For a reader, it
makes sure that the next read will be from disk rather than from
previously cached buffers, so that the reader will see changes made by
the writing process (e.g., the number of records written) without
having to close and reopen the dataset. If you are only accessing a
small amount of data, it can be expensive in computer resources to
always synchronize to disk after every write, since you are giving up
the benefits of buffering.

An easier way to accomplish sharing (and what is now recommended) is
to have the writer and readers open the dataset with the NC_SHARE
flag, and then it will not be necessary to call nc_sync at
all. However, the nc_sync function still provides finer granularity
than the NC_SHARE flag, if only a few netCDF accesses need to be
synchronized among processes.

It is important to note that changes to the ancillary data, such as
attribute values, are not propagated automatically by use of the
NC_SHARE flag. Use of the nc_sync function is still required for this
purpose.

Sharing datasets when the writer enters define mode to change the data
schema requires extra care. In previous releases, after the writer
left define mode, the readers were left looking at an old copy of the
dataset, since the changes were made to a new copy. The only way
readers could see the changes was by closing and reopening the
dataset. Now the changes are made in place, but readers have no
knowledge that their internal tables are now inconsistent with the new
dataset schema. If netCDF datasets are shared across redefinition,
some mechanism external to the netCDF library must be provided that
prevents access by readers during redefinition and causes the readers
to call nc_sync before any subsequent access.

When calling nc_sync, the netCDF dataset must be in data mode. A
netCDF dataset in define mode is synchronized to disk only when
nc_enddef is called. A process that is reading a netCDF dataset that
another process is writing may call nc_sync to get updated with the
changes made to the data by the writing process (e.g., the number of
records written), without having to close and reopen the dataset.

Data is automatically synchronized to disk when a netCDF dataset is
closed, or whenever you leave define mode.

@heading Usage 
@example
int nc_sync(int ncid);
@end example

@table @code
@item ncid
NetCDF ID, from a previous call to nc_open or nc_create.
@end table

@heading Errors 

nc_sync returns the value NC_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
The netCDF dataset is in define mode. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Example 

Here is an example using nc_sync to synchronize the disk writes of a
netCDF dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int status;
int ncid;
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);  /* open for writing */
if (status != NC_NOERR) handle_error(status);

   ...           /* write data or change attributes */

status = nc_sync(ncid);      /* synchronize to disk */
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_abort, nc_set_fill, nc_sync, Datasets
@section Back Out of Recent Definitions: nc_abort 
@findex nc_abort
@cindex nc_abort, example
@cindex backing out of definitions
@cindex canceling definitions

You no longer need to call this function, since it is called
automatically by nc_close in case the dataset is in define mode and
something goes wrong with committing the changes. The function
nc_abort just closes the netCDF dataset, if not in define mode. If the
dataset is being created and is still in define mode, the dataset is
deleted. If define mode was entered by a call to nc_redef, the netCDF
dataset is restored to its state before definition mode was entered
and the dataset is closed.

@heading Usage 
@example
int nc_abort(int ncid);
@end example

@table @code
@item ncid
NetCDF ID, from a previous call to nc_open or nc_create.
@end table

@heading Errors 

nc_abort returns the value NC_NOERR if no errors occurred. Otherwise,
the returned status indicates an error. Possible causes of errors
include:
@itemize

@item
When called from define mode while creating a netCDF dataset, deletion
of the dataset failed.

@item
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Example 

Here is an example using nc_abort to back out of redefinitions of a
dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int ncid, status, latid;
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);/* open for writing */
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_redef(ncid);                    /* enter define mode */
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_def_dim(ncid, "lat", 18L, &latid);
if (status != NC_NOERR) @{
   handle_error(status);
   status = nc_abort(ncid);                 /* define failed, abort */
   if (status != NC_NOERR) handle_error(status);
@}
@end example

@node nc_set_fill, nc_set_default_format, nc_abort, Datasets
@section Set Fill Mode for Writes: nc_set_fill 
@findex nc_set_fill
@cindex nc_set_fill, example
@cindex write fill mode, setting

This function is intended for advanced usage, to optimize writes under
some circumstances described below. The function nc_set_fill sets the
fill mode for a netCDF dataset open for writing and returns the
current fill mode in a return parameter. The fill mode can be
specified as either NC_FILL or NC_NOFILL. The default behavior
corresponding to NC_FILL is that data is pre-filled with fill values,
that is fill values are written when you create non-record variables
or when you write a value beyond data that has not yet been
written. This makes it possible to detect attempts to read data before
it was written. For more information on the use of fill values
see @ref{Fill Values}. For information about how to define your own fill
values see @ref{Attribute Conventions,,, netcdf, NetCDF
Users' Guide}.

The behavior corresponding to NC_NOFILL overrides the default behavior
of prefilling data with fill values. This may enhance
performance, because it avoids the duplicate writes that occur when
the netCDF library writes fill values that are later overwritten with
data, at the cost of losing the ability to later detect access of
values that were never written.

A value indicating which mode the netCDF dataset was already in is
returned. You can use this value to temporarily change the fill mode
of an open netCDF dataset and then restore it to the previous mode.

After you turn on NC_NOFILL mode for an open netCDF dataset, you must
be certain to write valid data in all the positions that will later be
read. Note that nofill mode is only a transient property of a netCDF
dataset open for writing: if you close and reopen the dataset, it will
revert to the default behavior. You can also revert to the default
behavior by calling nc_set_fill again to explicitly set the fill mode
to NC_FILL.

There are three situations where it might be advantageous to set nofill
mode:

@enumerate

@item
Creating and initializing a netCDF dataset. In this case, you could
set nofill mode before calling nc_enddef and then write completely all
non-record variables and the initial records of all the record
variables you want to initialize.

@item
Extending an existing record-oriented netCDF dataset. Set nofill mode
after opening the dataset for writing, then append the additional
records to the dataset completely, leaving no intervening unwritten
records.

@item
Adding new variables that you are going to initialize to an existing
netCDF dataset. Set nofill mode before calling nc_enddef then write
all the new variables completely.

@end enumerate

If the netCDF dataset has an unlimited dimension and the last record
was written while in nofill mode, then the dataset may be shorter than
if nofill mode was not set, but this will be completely transparent if
you access the data only through the netCDF interfaces.

The use of this feature may not be available (or even needed) in
future releases. Programmers are cautioned against heavy reliance upon
this feature.

@heading Usage 
@example
int nc_set_fill (int ncid, int fillmode, int *old_modep);
@end example

@table @code
@item ncid
NetCDF ID, from a previous call to nc_open or nc_create.
 
@item fillmode
Desired fill mode for the dataset, either NC_NOFILL or NC_FILL.
 
@item old_modep
Pointer to location for returned current fill mode of the dataset
before this call, either NC_NOFILL or NC_FILL.
@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
The specified netCDF ID does not refer to an open netCDF dataset. 

@item NC_EPERM
The specified netCDF ID refers to a dataset open for read-only access. 

@item NC_EINVAL
The fill mode argument is neither NC_NOFILL nor NC_FILL.

@end table

@heading Example 

Here is an example using nc_set_fill to set nofill mode for subsequent
writes of a netCDF dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int ncid, status, old_fill_mode;
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);  /* open for writing */
if (status != NC_NOERR) handle_error(status);

   ...           /* write data with default prefilling behavior */

status = nc_set_fill(ncid, NC_NOFILL, &old_fill_mode); /* set nofill */
if (status != NC_NOERR) handle_error(status);

   ...           /* write data with no prefilling */
@end example

@node nc_set_default_format, nc_set_chunk_cache, nc_set_fill, Datasets
@section Set Default Creation Format: nc_set_default_format
@findex nc_set_default_format
@cindex nc_set_default_format, example
@cindex create flag, setting default

This function is intended for advanced users. 

Starting in version 3.6, netCDF introduced a new data format, the
first change in the underlying binary data format since the netCDF
interface was released. The new format, 64-bit offset format, was
introduced to greatly relax the limitations on creating very large
files.

Users are warned that creating files in the 64-bit offset format makes
them unreadable by the netCDF library prior to version 3.6.0. For
reasons of compatibility, users should continue to create files in
netCDF classic format.

Users who do want to use 64-bit offset format files can create them
directory from nc_create, using the proper cmode flag.
(@pxref{nc_create}).

The function nc_set_default_format allows the user to change the
format of the netCDF file to be created by future calls to nc_create
(or nc__create) without changing the cmode flag.

This allows the user to convert a program to use 64-bit offset
formation without changing all calls the nc_create. @xref{Large File
Support,,, netcdf, @value{n-man}}.

Once the default format is set, all future created files will be in
the desired format.

Two constants are provided in the netcdf.h file to be used with this
function, NC_FORMAT_64BIT and NC_FORMAT_CLASSIC.

If a non-NULL pointer is provided, it is assumed to point to an int,
where the existing default format will be written.

Using nc_create with a cmode including NC_64BIT_OFFSET overrides the
default format, and creates a 64-bit offset file.

@heading Usage 

@example
int nc_set_default_format(int format, int *old_formatp);
@end example

@table @code

@item format
Valid formats include NC_FORMAT_CLASSIC (the default),
NC_FORMAT_64BIT, and, if --enable-netcdf-4 was used during configure,
NC_FORMAT_NETCDF4 and NC_FORMAT_NETCDF4_CLASSIC

@item old_formatp
Either NULL (in which case it will be ignored), or a pointer to an int
where the existing default format (i.e. before being changed to the
new format) will be written. This allows you to get the existing
default format while setting a new default format.

@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item NC_EINVAL
Invalid format. Valid formats include NC_FORMAT_CLASSIC,
NC_FORMAT_64BIT, and, if --enable-netcdf-4 was used during configure,
NC_FORMAT_NETCDF4 and NC_FORMAT_NETCDF4_CLASSIC. Trying to set the
default format to something else will result in an invalid argument
error.

@end table

@heading Example 

Here is an example using nc_set_default_format to create the same file
in four formats with the same nc_create call (from libsrc4/tst_utf8.c):

@example
#include <netcdf.h>
   ... 
      int ncid, varid, dimids[NDIMS];
      int f;

      for (f = NC_FORMAT_CLASSIC; f < NC_FORMAT_NETCDF4_CLASSIC; f++)
      @{
         if (nc_set_default_format(f, NULL)) ERR;
         if (nc_create(FILE_NAME, NC_CLOBBER, &ncid)) ERR;
   ... 
@end example

@node nc_set_chunk_cache, nc_get_chunk_cache, nc_set_default_format, Datasets
@section Set HDF5 Chunk Cache for Future File Opens/Creates: nc_set_chunk_cache
@findex nc_set_chunk_cache
@cindex HDF5 chunk cache

This function changes the default chunk cache settings in the HDF5
library for all variables in the file. The settings apply for
subsequent file opens/creates. This function does not change the chunk
cache settings of already open files.

For more information, see the documentation for the H5Pset_cache()
function in the HDF5 library at the HDF5 website:
@uref{@value{hdf5-url}}.

@heading Usage 

@example
int nc_set_chunk_cache(size_t size, size_t nelems, float preemption);
@end example

@table @code

@item size
The total size of the raw data chunk cache, in bytes. This should be
big enough to hold multiple chunks of data.

@item nelems
The number of chunk slots in the raw data chunk cache hash table. This
should be a prime number larger than the number of chunks that will be
in the cache.

@item preemption
The preemtion value must be between 0 and 1 inclusive and indicates
how much chunks that have been fully read are favored for
preemption. A value of zero means fully read chunks are treated no
differently than other chunks (the preemption is strictly LRU) while a
value of one means fully read chunks are always preempted before other
chunks. 

@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item NC_EINVAL
Preemption must be between zero and one (inclusive). 

@end table

@heading Example 

This example is from libsrc4/tst_files.c:

@example
#include <netcdf.h>
   ... 
#define NEW_CACHE_SIZE 32000000
#define NEW_CACHE_NELEMS 2000
#define NEW_CACHE_PREEMPTION .75

   /* Change chunk cache. */
   if (nc_set_chunk_cache(NEW_CACHE_SIZE, NEW_CACHE_NELEMS, 
			  NEW_CACHE_PREEMPTION)) ERR;

   /* Create a file with two dims, two vars, and two atts. */
   if (nc_create(FILE_NAME, cflags|NC_CLOBBER, &ncid)) ERR;

   ... 
@end example

@node nc_get_chunk_cache,  , nc_set_chunk_cache, Datasets
@section Get the HDF5 Chunk Cache Settings for Future File Opens/Creates: nc_get_chunk_cache
@findex nc_get_chunk_cache
@cindex HDF5 chunk cache

This function gets the chunk cache settings for the HDF5
library. The settings apply for subsequent file opens/creates. 

This affects the per-file chunk cache which the HDF5 layer
maintains. The chunk cache size can be tuned for better performance.

For more information, see the documentation for the H5Pget_cache()
function in the HDF5 library at the HDF5 website:
@uref{@value{hdf5-url}}.

@heading Usage 

@example
int nc_get_chunk_cache(size_t *sizep, size_t *nelemsp, float *preemptionp);
@end example

@table @code

@item sizep
The total size of the raw data chunk cache will be put here. If NULL,
will be ignored.

@item nelemsp
The number of chunk slots in the raw data chunk cache hash table will
be put here.  If NULL, will be ignored.


@item preemptionp
The preemption will be put here.  The preemtion value is between 0 and
1 inclusive and indicates how much chunks that have been fully read
are favored for preemption.  A value of zero means fully read chunks
are treated no differently than other chunks (the preemption is
strictly LRU) while a value of one means fully read chunks are always
preempted before other chunks.  If NULL, will be ignored.

@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@end table

@heading Example 

This example is from libsrc4/tst_files.c:

@example
#include <netcdf.h>
   ... 
   /* Retrieve the chunk cache settings, just for fun. */
   if (nc_get_chunk_cache(&cache_size_in, &cache_nelems_in, 
			  &cache_preemption_in)) ERR;
   if (cache_size_in != NEW_CACHE_SIZE || cache_nelems_in != NEW_CACHE_NELEMS ||
       cache_preemption_in != NEW_CACHE_PREEMPTION) ERR;

   ... 
@end example

@node Groups, Dimensions, Datasets, Top
@chapter Groups
@cindex groups, overview

NetCDF-4 added support for hierarchical groups within netCDF
datasets. 

Groups are identified with a ncid, which identifies both the open
file, and the group within that file. When a file is opened with
nc_open or nc_create, the ncid for the root group of that file is
provided. Using that as a starting point, users can add new groups, or
list and navigate existing groups.

All netCDF calls take a ncid which determines where the call will
take its action. For example, the nc_def_var function takes a ncid as
its first parameter. It will create a variable in whichever group
its ncid refers to. Use the root ncid provided by nc_create or
nc_open to create a variable in the root group. Or use nc_def_grp to
create a group and use its ncid to define a variable in the new
group.

Variable are only visible in the group in which they are
defined. The same applies to attributes. ``Global'' attributes are
associated with the group whose ncid is used. 

Dimensions are visible in their groups, and all child groups.

Group operations are only permitted on netCDF-4 files - that is, files
created with the HDF5 flag in nc_create. (@pxref{nc_create}). Groups
are not compatible with the netCDF classic data model, so files
created with the NC_CLASSIC_MODEL file cannot contain groups (except
the root group).

@menu
* nc_inq_ncid::                 
* nc_inq_grps::                 
* nc_inq_varids::               
* nc_inq_dimids::               
* nc_inq_grpname::              
* nc_inq_grpname_full::         
* nc_inq_grpname_len::          
* nc_inq_grp_parent::           
* nc_inq_grp_ncid::             
* nc_inq_grp_full_ncid::        
* nc_def_grp::                  
@end menu

@node nc_inq_ncid, nc_inq_grps, Groups, Groups
@section Find a Group ID: nc_inq_ncid
@findex nc_inq_ncid

Given an ncid and group name (NULL or "" gets root group), return
ncid of the named group.

@heading Usage 

@example
int nc_inq_ncid(int ncid, const char *name, int *grp_ncid);
@end example

@table @code

@item ncid
The group id for this operation.

@item name
A char array that holds the name of the desired group.

@item grp_ncid
An int pointer that will receive the group id, if the group is found. 

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
   int root_ncid, child_ncid;
   char file[] = "nc4_test.nc";

   /* Open the file. */
   if ((res = nc_open(file, NC_NOWRITE, &root_ncid)))
      return res;

   /* Get the ncid of an existing group. */
   if ((res = nc_inq_ncid(root_ncid, "group1", &child_ncid)))
      return res;
@end example

@node nc_inq_grps, nc_inq_varids, nc_inq_ncid, Groups
@section Get a List of Groups in a Group: nc_inq_grps
@findex nc_inq_grps

Given a location id, return the number of groups it contains, and an
array of their ncids.

@heading Usage 

@example
int nc_inq_grps(int ncid, int *numgrps, int *ncids);
@end example

@table @code

@item ncid
The group id for this operation.

@item numgrps
Pointer to an int which will get number of groups in this group. If
NULL, it's ignored.

@item ncids
Pointer to a already  allocated array of ints which will receive the
ids of all the groups in this group. If NULL, it's ignored. Call this
function with NULL for ncids parameter to find out how many groups
there are.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
   int root_ncid, numgrps;
   int *ncids;
   char file[] = "nc4_test.nc";

   /* Open the file. */
   if ((res = nc_open(file, NC_NOWRITE, &root_ncid)))
      return res;

   /* Get a list of ncids for the root group. (That is, find out of
      there are any groups already defined. */
   if ((res = nc_inq_grps(root_ncid, &numgrps, NULL)))
      return res;
   ncids = malloc(sizeof(int) * numgrps);
   if ((res = nc_inq_grps(root_ncid, NULL, ncids)))
      return res;
@end example

@node nc_inq_varids, nc_inq_dimids, nc_inq_grps, Groups
@section Find all the Variables in a Group: nc_inq_varids
@findex nc_inq_varids

Find all varids for a location.

@heading Usage 

@example
nc_inq_varids(int ncid, int *nvars, int *varids);
@end example

@table @code

@item ncid
The group id for this operation.

@item nvars
The integer pointed to by this parameter will get the number of
variable IDs found.

@item varids
An already allocated array to store the list of varids. Ignored if
NULL.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

This example is from libsrc4/tst_vars.c.

@example
      int nvars_in, varids_in[2];

      ...

      /* Open the file and make sure nc_inq_varids yeilds correct
       * result. */
      if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;
      if (nc_inq_varids(ncid, &nvars_in, varids_in)) ERR;
@end example

@node nc_inq_dimids, nc_inq_grpname, nc_inq_varids, Groups
@section Find all Dimensions Visible in a Group: nc_inq_dimids
@findex nc_inq_dimids

Find all dimids for a location. This finds all dimensions in a group,
or any of its parents.

@heading Usage 

@example
int nc_inq_dimids(int ncid, int *ndims, int *dimids, int include_parents);
@end example

@table @code

@item ncid
The group id for this operation.

@item ndims
If non-zero, pointer to location for returned number of dimensions defined for this
location, including dimensions inherited from parent groups if
include_parents is non-zero.

@item dimids
An already allocated array of ints when the dimids of the visible
dimensions will be stashed. Use nc_inq_ndims to find out how many dims
are visible from this group. (@pxref{nc_inq Family}).

@item include_parents
If non-zero then all the dimensions in all parent groups will also be
retrieved.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

This example is from libsrc4/tst_dims.c.

@example
      int ncid, dimid;
      int ndims_in, dimids_in[MAX_DIMS];

      ...

      /* Open the file and make sure nc_inq_dimids yeilds correct
       * result. */
      if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;
      if (nc_inq_dimids(ncid, &ndims_in, dimids_in, 0)) ERR;
      if (ndims_in != 1 || dimids_in[0] != 0) ERR;
@end example

@node nc_inq_grpname, nc_inq_grpname_full, nc_inq_dimids, Groups
@section Find a Group's Name: nc_inq_grpname
@findex nc_inq_grpname

Given a group ID find its name. (Root group is named
"/"). @xref{nc_inq_grpname_full}.

@heading Usage 

@example
int nc_inq_grpname(int ncid, char *name);
@end example

@table @code

@item ncid
The group id for this operation.

@item name
Pointer to allocated space of correct length. The name of the
group will be copied there. The name will be less than NC_MAX_NAME,
not including a terminating NULL byte.
@item

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

This example is from libsrc4/tst_grps.c.

@example
      int grpid_in[MAX_SIBLING_GROUPS];
      char name_in[NC_MAX_NAME + 1];

      ...

      if (nc_inq_grpname(grpid_in[0], name_in)) ERR;
@end example

@node nc_inq_grpname_full, nc_inq_grpname_len, nc_inq_grpname, Groups
@section Find a Group's Full Name: nc_inq_grpname_full
@findex nc_inq_grpname_full

Given ncid, find complete name of group. (Root group is named "/", a
full "path" for each group is provided in the name, with groups
separated with a forward slash / as in Unix directory names. For
example "/group1/subgrp1/subsubgrp1")

@heading Usage 

@example
int nc_inq_grpname_full(int ncid, size_t *lenp, char *full_name);
@end example

@table @code

@item ncid
The group id for this operation.

@item lenp
Pointer to a size_t which will get the length. (Note that this does
not include the NULL terminator byte.)

@item full_name
Pointer to allocated space of correct length. The name of the
group will be copied there. To find the required length, call
nc_inq_grpname_len call this function with NULL for the full_name
parameter, or call (@pxref{nc_inq_grpname_len}).

@item

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

This example is from the test program libsrc4/tst_grps.c.

@example
      int grpid_in[MAX_SIBLING_GROUPS];
      char full_name_in[NC_MAX_NAME * 10]; 
      size_t len;

      ...

      if (nc_inq_grpname_full(grpid_in[0], &len, full_name_in)) ERR;
@end example

@node nc_inq_grpname_len, nc_inq_grp_parent, nc_inq_grpname_full, Groups
@section Find the Length of a Group's Full Name: nc_inq_grpname_len
@findex nc_inq_grpname_len

Given ncid, find len of the full name, as returned by
nc_inq_grpname_full @xref{nc_inq_grpname_full}. (Root group is named "/", with length 1.) 

@heading Usage 

@example
int nc_inq_grpname_len(int ncid, size_t *lenp);
@end example

@table @code

@item ncid
The group id for this operation.

@item lenp
Pointer to an int where the length will be placed. Length does not
include NULL terminator.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

This example is from libsrc4/tst_grps.c.

@example
      int ncid;
      size_t len;

      ...

      if (nc_inq_grpname_len(ncid, &len)) ERR;
@end example

@node nc_inq_grp_parent, nc_inq_grp_ncid, nc_inq_grpname_len, Groups
@section Find a Group's Parent: nc_inq_grp_parent
@findex nc_inq_grp_parent

Given ncid, find the ncid of the parent group. 

When used with the root group, this function returns the NC_ENOGRP
error (since the root group has no parent.)

@heading Usage 

@example
int nc_inq_grp_parent(int ncid, int *parent_ncid);
@end example

@table @code

@item ncid
The group id.

@item parent_ncid
Pointer to an int. The ncid of the group will be copied there.
@item

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENOGRP
No parent group found (i.e. this is the root group).

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
   if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
   if (nc_def_grp(ncid, HENRY_VII, &henry_vii_id)) ERR;

   if (nc_inq_grp_parent(henry_vii_id, &parent_ncid)) ERR;
   if (parent_ncid != ncid) ERR;
   if (nc_close(ncid)) ERR;
@end example

@node nc_inq_grp_ncid, nc_inq_grp_full_ncid, nc_inq_grp_parent, Groups
@section Find a Group by Name: nc_inq_grp_ncid
@findex nc_inq_grp_parent

Given a group location id and the name of an immediate subgroup, find
the location id of the named subgroup. 

@heading Usage 

@example
int nc_inq_grp_ncid(int ncid, const char *grp_name, int *grp_ncid);
@end example

@table @code

@item ncid
The location id of the group in which to look.

@item grp_name
The name of a subgroup.

@item grp_ncid
A pointer to int which will get the group id of the named subgroup, if it is found.

@end table

@heading Return Codes

The following return codes may be returned by this function.

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_EINVAL
No name provided or name longer than NC_MAX_NAME.

@item NC_ENOGRP
Named subgroup not found.

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example
This example is from test program libsrc4/tst_grps.c.

@example
      /* Reopen and recheck. */
      if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;      
      if (nc_inq_grp_ncid(ncid, SCI_FI, &g1id)) ERR;
@end example

@node nc_inq_grp_full_ncid, nc_def_grp, nc_inq_grp_ncid, Groups
@section Find a Group by its Fully-qualified Name: nc_inq_grp_full_ncid
@findex nc_inq_grp_parent

Given a fully qualified group name and an ncid, find the ncid of the
group id.

@heading Usage 

@example
int nc_inq_grp_full_ncid(int ncid, char *full_name, int *grp_ncid);
@end example

@table @code

@item ncid
The group id to look in.

@item full_name
The fully-qualified group name.

@item grp_ncid
A pointer to int which will get the group id, if it is found.

@end table

@heading Return Codes

The following return codes may be returned by this function.

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_EINVAL
No name provided or name longer than NC_MAX_NAME.

@item NC_ENOGRP
Named group not found.

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example
This example is from test program libsrc4/tst_grps.c.

@example
      /* Reopen and recheck. */
      if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;      
      if (nc_inq_grp_ncid(ncid, SCI_FI, &g1id)) ERR;
@end example

@node nc_def_grp,  , nc_inq_grp_full_ncid, Groups
@section Create a New Group: nc_def_grp
@findex nc_def_grp

Create a group. Its location id is returned in the new_ncid pointer. 

@heading Usage 

@example
int nc_def_grp(int parent_ncid, const char *name, int *new_ncid);
@end example

@table @code

@item parent_ncid
The group id of the parent group.

@item name
The name of the new group.  A group cannot have the same name as a
variable within the same parent group.

@item new_ncid
A pointer to an int. The ncid of the new group will be placed there.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENAMEINUSE
That name is in use. Group names must be unique within a group, and
must not be the same as any variable or type in the group.

@item NC_EMAXNAME
Name exceed max length NC_MAX_NAME.

@item NC_EBADNAME
Name contains illegal characters.

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@item NC_EPERM
Attempt to write to a read-only file.

@item NC_ENOTINDEFINE
Not in define mode.

@end table

@heading Example

@example
      int ncid, a1_ncid;
      char grpname[] = "assimilation1";

      /* Create a group. */
      if ((res = nc_def_grp(ncid, grpname, &a1_ncid)))
         return res;
@end example

@node Dimensions, User Defined Data Types, Groups, Top
@chapter Dimensions

@menu
* Dimensions Introduction::     
* nc_def_dim::                  Create a Dimension
* nc_inq_dimid::                Get a Dimension ID from Its Name
* nc_inq_dim Family::           Inquire about a Dimension
* nc_rename_dim::               Rename a Dimension
* nc_inq_unlimdims::            
@end menu

@node Dimensions Introduction, nc_def_dim, Dimensions, Dimensions
@section Dimensions Introduction

Dimensions for a netCDF dataset are defined when it is created, while
the netCDF dataset is in define mode. Additional dimensions may be
added later by reentering define mode. A netCDF dimension has a name
and a length. In a netCDF classic or 64-bit offset file, at most one
dimension can have the unlimited length, which means variables using
this dimension can grow along this dimension. In a netCDF-4 file
multiple unlimited dimensions are supported.

There is a suggested limit (100) to the number of dimensions that can
be defined in a single netCDF dataset. The limit is the value of the
predefined macro NC_MAX_DIMS. The purpose of the limit is to make
writing generic applications simpler. They need only provide an array
of NC_MAX_DIMS dimensions to handle any netCDF dataset. The
implementation of the netCDF library does not enforce this advisory
maximum, so it is possible to use more dimensions, if necessary, but
netCDF utilities that assume the advisory maximums may not be able to
handle the resulting netCDF datasets.

Ordinarily, the name and length of a dimension are fixed when the
dimension is first defined. The name may be changed later, but the
length of a dimension (other than the unlimited dimension) cannot be
changed without copying all the data to a new netCDF dataset with a
redefined dimension length.

Dimension lengths in the C interface are type size_t rather than type
int to make it possible to access all the data in a netCDF dataset on
a platform that only supports a 16-bit int data type, for example
MSDOS. If dimension lengths were type int instead, it would not be
possible to access data from variables with a dimension length greater
than a 16-bit int can accommodate.

A netCDF dimension in an open netCDF dataset is referred to by a small
integer called a dimension ID. In the C interface, dimension IDs are
0, 1, 2, ..., in the order in which the dimensions were defined.

Operations supported on dimensions are:
@itemize

@item
Create a dimension, given its name and length. 

@item
Get a dimension ID from its name. 

@item
Get a dimension's name and length from its ID. 

@item
Rename a dimension. 
@end itemize

@node nc_def_dim, nc_inq_dimid, Dimensions Introduction, Dimensions
@section Create a Dimension: nc_def_dim 
@findex nc_def_dim
@cindex nc_def_dim, example

The function nc_def_dim adds a new dimension to an open netCDF dataset
in define mode. It returns (as an argument) a dimension ID, given the
netCDF ID, the dimension name, and the dimension length. At most one
unlimited length dimension, called the record dimension, may be
defined for each classic or 64-bit offset netCDF dataset. NetCDF-4
datasets may have multiple unlimited dimensions.

@heading Usage 
@example
int nc_def_dim (int ncid, const char *name, size_t len, int *dimidp);
@end example

@table @code
@item ncid
NetCDF group ID, from a previous call to nc_open, nc_create,
nc_def_grp, etc.
 
@item name
Dimension name.
 
@item len
Length of dimension; that is, number of values for this dimension as
an index to variables that use it. This should be either a positive
integer (of type size_t) or the predefined constant NC_UNLIMITED.
 
@item dimidp
Pointer to location for returned dimension ID.
@end table

@heading Errors 

nc_def_dim returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:
@itemize

@item
The netCDF dataset is not in definition mode. 

@item
The specified dimension name is the name of another existing
dimension.

@item
The specified length is not greater than zero. 

@item
The specified length is unlimited, but there is already an unlimited
length dimension defined for this netCDF dataset.

@item
The specified netCDF ID does not refer to an open netCDF dataset.

@end itemize

@heading Example

Here is an example using nc_def_dim to create a dimension named lat of
length 18 and a unlimited dimension named rec in a new netCDF dataset
named foo.nc:

@example
#include <netcdf.h>
   ... 
int status, ncid, latid, recid;
   ... 
status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_def_dim(ncid, "lat", 18L, &latid);
if (status != NC_NOERR) handle_error(status);
status = nc_def_dim(ncid, "rec", NC_UNLIMITED, &recid);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_inq_dimid, nc_inq_dim Family, nc_def_dim, Dimensions
@section Get a Dimension ID from Its Name: nc_inq_dimid 
@findex nc_inq_dimid
@cindex nc_inq_dimid, example

The function nc_inq_dimid returns (as an argument) the ID of a netCDF
dimension, given the name of the dimension. If ndims is the number of
dimensions defined for a netCDF dataset, each dimension has an ID
between 0 and ndims-1.


@heading Usage 

When searching for a dimension, the specified group is searched, and
then its parent group, and then its grandparent group, etc., up to
the root group.

@example
int nc_inq_dimid (int ncid, const char *name, int *dimidp);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item name
Dimension name.
 
@item dimidp
Pointer to location for the returned dimension ID.

@end table
 
@heading Errors 

nc_inq_dimid returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

The name that was specified is not the name of a dimension in the
netCDF dataset.  The specified netCDF ID does not refer to an open
netCDF dataset.

@heading Example

Here is an example using nc_inq_dimid to determine the dimension ID of
a dimension named lat, assumed to have been defined previously in an
existing netCDF dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int status, ncid, latid;
   ... 
status = nc_open("foo.nc", NC_NOWRITE, &ncid);  /* open for reading */
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_dimid(ncid, "lat", &latid);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_inq_dim Family, nc_rename_dim, nc_inq_dimid, Dimensions
@section Inquire about a Dimension: nc_inq_dim Family
@findex nc_inq_dim Family
@findex nc_inq_dim
@findex nc_inq_dimid
@findex nc_inq_dimids
@findex nc_inq_dimlen
@findex nc_inq_dimname
@cindex nc_inq_dim Family, example

This family of functions returns information about a netCDF
dimension. Information about a dimension includes its name and its
length. The length for the unlimited dimension, if any, is the number
of records written so far.

The functions in this family include nc_inq_dim, nc_inq_dimname, and
nc_inq_dimlen. The function nc_inq_dim returns all the information
about a dimension; the other functions each return just one item of
information.

@heading Usage 
@example
int nc_inq_dim     (int ncid, int dimid, char* name, size_t* lengthp);
int nc_inq_dimname (int ncid, int dimid, char *name);
int nc_inq_dimlen  (int ncid, int dimid, size_t *lengthp);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item dimid
Dimension ID, from a previous call to nc_inq_dimid or nc_def_dim.
 
@item name
Returned dimension name. The caller must allocate space for the
returned name. The maximum possible length, in characters, of a
dimension name is given by the predefined constant NC_MAX_NAME. (This
doesn't include the null terminator, so declare your array to be size
NC_MAX_NAME+1). The returned character array will be null-terminated.
 
@item lengthp
Pointer to location for returned length of dimension. For the
unlimited dimension, this is the number of records written so far.

@end table

@heading Errors 

These functions return the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The dimension ID is invalid for the specified netCDF dataset. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@end itemize

@heading Example

Here is an example using nc_inq_dim to determine the length of a
dimension named lat, and the name and current maximum length of the
unlimited dimension for an existing netCDF dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int status, ncid, latid, recid;
size_t latlength, recs;
char recname[NC_MAX_NAME+1];
   ... 
status = nc_open("foo.nc", NC_NOWRITE, &ncid);  /* open for reading */
if (status != NC_NOERR) handle_error(status);
status = nc_inq_unlimdim(ncid, &recid); /* get ID of unlimited dimension */
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_dimid(ncid, "lat", &latid);  /* get ID for lat dimension */
if (status != NC_NOERR) handle_error(status);
status = nc_inq_dimlen(ncid, latid, &latlength); /* get lat length */
if (status != NC_NOERR) handle_error(status);
/* get unlimited dimension name and current length */
status = nc_inq_dim(ncid, recid, recname, &recs);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_rename_dim, nc_inq_unlimdims, nc_inq_dim Family, Dimensions
@section Rename a Dimension: nc_rename_dim 
@findex nc_rename_dim
@cindex nc_rename_dim, example

The function nc_rename_dim renames an existing dimension in a netCDF
dataset open for writing. You cannot rename a dimension to have the
same name as another dimension.

For netCDF classic and 64-bit offset files, if the new name is longer
than the old name, the netCDF dataset must be in define mode.

For netCDF-4 files the dataset is switched to define more for the
rename, regardless of the name length.

@heading Usage 
int nc_rename_dim(int ncid, int dimid, const char* name);

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item dimid
Dimension ID, from a previous call to nc_inq_dimid or nc_def_dim.
 
@item name
New dimension name.

@end table

@heading Errors 
nc_rename_dim returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The new name is the name of another dimension. 

@item
The dimension ID is invalid for the specified netCDF dataset. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@item
The new name is longer than the old name and the netCDF dataset is not in define mode. 
@end itemize

@heading Example

Here is an example using nc_rename_dim to rename the dimension lat to
latitude in an existing netCDF dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int status, ncid, latid;
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);  /* open for writing */
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_redef(ncid);  /* put in define mode to rename dimension */
if (status != NC_NOERR) handle_error(status);
status = nc_inq_dimid(ncid, "lat", &latid);
if (status != NC_NOERR) handle_error(status);
status = nc_rename_dim(ncid, latid, "latitude");
if (status != NC_NOERR) handle_error(status);
status = nc_enddef(ncid); /* leave define mode */
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_inq_unlimdims,  , nc_rename_dim, Dimensions
@section Find All Unlimited Dimension IDs: nc_inq_unlimdims
@findex nc_inq_unlimdims

In netCDF-4 files, it's possible to have multiple unlimited
dimensions. This function returns a list of the unlimited dimension
ids visible in a group.

Dimensions are visible in a group if they have been defined in that
group, or any ancestor group.

@heading Usage 

@example
int nc_inq_unlimdims(int ncid, int *nunlimdimsp, int *unlimdimidsp);
@end example

@table @code

@item ncid
NetCDF group ID, from a previous call to nc_open, nc_create,
nc_def_grp, etc.
 
@item nunlimdimsp
A pointer to an int which will get the number of visible unlimited
dimensions. Ignored if NULL.
 
@item unlimdimidsp
A pointer to an already allocated array of int which will get the ids
of all visible unlimited dimensions. Ignored if NULL. To allocate the
correct length for this array, call nc_inq_unlimdims with a NULL for
this parameter and use the nunlimdimsp parameter to get the number of
visible unlimited dimensions.

@end table

@heading Errors 

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag HDF5. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
   int root_ncid, num_unlimdims, unlimdims[NC_MAX_DIMS];
   char file[] = "nc4_test.nc";
   int res;

   /* Open the file. */
   if ((res = nc_open(file, NC_NOWRITE, &root_ncid)))
      return res;

   /* Find out if there are any unlimited dimensions in the root
      group. */
   if ((res = nc_inq_unlimdims(root_ncid, &num_unlimdims, unlimdims)))
      return res;

   printf("nc_inq_unlimdims reports %d unlimited dimensions\n", num_unlimdims);
@end example

@node User Defined Data Types, Variables, Dimensions, Top
@chapter User Defined Data Types
@cindex variable length array type, overview
@cindex user defined types

@menu
* User Defined Types::          
* nc_inq_typeids::              
* nc_inq_typeid::               
* nc_inq_type::                 
* nc_inq_user_type::            
* Compound Types::              
* nc_def_compound::             
* nc_insert_compound::          
* nc_insert_array_compound::    
* nc_inq_compound::             
* nc_inq_compound_name::        
* nc_inq_compound_size::        
* nc_inq_compound_nfields::     
* nc_inq_compound_field::       
* nc_inq_compound_fieldname::   
* nc_inq_compound_fieldindex::  
* nc_inq_compound_fieldoffset::  
* nc_inq_compound_fieldtype::   
* nc_inq_compound_fieldndims::  
* nc_inq_compound_fielddim_sizes::  
* Variable Length Array::       
* nc_def_vlen::                 
* nc_inq_vlen::                 
* nc_free_vlen::                
* nc_free_vlens::               
* Opaque Type::                 
* nc_def_opaque::               
* nc_inq_opaque::               
* Enum Type::                   
* nc_def_enum::                 
* nc_insert_enum::              
* nc_inq_enum::                 
* nc_inq_enum_member::          
* nc_inq_enum_ident::           
@end menu

@node User Defined Types, nc_inq_typeids, User Defined Data Types, User Defined Data Types
@section User Defined Types Introduction
@cindex user defined types, overview

NetCDF-4 has added support for four different user defined data
types. User defined type may only be used in files created with the
NC_NETCDF4 and without NC_CLASSIC_MODEL.

@table @code

@item compound type
Like a C struct, a compound type is a collection of types, including
other user defined types, in one package.

@item variable length array type
The variable length array may be used to store ragged arrays.

@item opaque type
This type has only a size per element, and no other type information.

@item enum type
Like an enumeration in C, this type lets you assign text values to
integer values, and store the integer values.

@end table

Users may construct user defined type with the various nc_def_*
functions described in this section. They may learn about user defined
types by using the nc_inq_ functions defined in this section.

Once types are constructed, define variables of the new type with
nc_def_var (@pxref{nc_def_var}). Write to them with nc_put_var1,
nc_put_var, nc_put_vara, or nc_put_vars (@pxref{Variables}). Read data
of user-defined type with nc_get_var1, nc_get_var, nc_get_vara, or
nc_get_vars (@pxref{Variables}).

Create attributes of the new type with nc_put_att
(@pxref{nc_put_att_ type}). Read attributes of the new type with nc_get_att
(@pxref{nc_get_att_ type}).

@node nc_inq_typeids, nc_inq_typeid, User Defined Types, User Defined Data Types
@section Learn the IDs of All Types in Group: nc_inq_typeids
@findex nc_inq_typeids

Learn the number of types defined in a group, and their IDs.

@heading Usage 

@example
int nc_inq_typeids(int ncid, int *ntypes, int *typeids);
@end example

@table @code

@item ncid
The group id.

@item ntypes
A pointer to int which will get the number of types defined in the
group. If NULL, ignored.

@item typeids
A pointer to an int array which will get the typeids. If NULL,
ignored.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_BADID
Bad ncid.

@end table

@heading Example

The following example is from the test program
libsrc4/tst_enums.c. 

@example
      if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;

      /* Get type info. */
      if (nc_inq_typeids(ncid, &ntypes, typeids)) ERR;
      if (ntypes != 1 || !typeids[0]) ERR;
@end example

@node nc_inq_typeid, nc_inq_type, nc_inq_typeids, User Defined Data Types
@section Find a Typeid from Group and Name: nc_inq_typeid
@findex nc_inq_typeid

Given a group ID and a type name, find the ID of the type. If the type
is not found in the group, then the parents are searched. If still not
found, the entire file is searched.

@heading Usage 

@example
int nc_inq_typeid(int ncid, const char *name, nc_type *typeidp);
@end example

@table @code

@item ncid
The group id.

@item name
The name of a type.

@item typeidp
A pointer to an int which will get the typeid.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad ncid.

@item NC_EBADTYPE
Can't find type.

@end table

@heading Example

The following example is from the test program
libsrc4/tst_vars.c. It tests that the correct names are given for
atomic types.

@example
	 /* Check inquire of atomic types */
	 if (nc_inq_type(ncid, NC_BYTE, name_in, &size_in)) ERR;
	 if (strcmp(name_in, "byte") || size_in != sizeof(char)) ERR;
	 if (nc_inq_type(ncid, NC_CHAR, name_in, &size_in)) ERR;
	 if (strcmp(name_in, "char") || size_in != sizeof(char)) ERR;
	 if (nc_inq_type(ncid, NC_SHORT, name_in, &size_in)) ERR;
	 if (strcmp(name_in, "short") || size_in != sizeof(short)) ERR;
	 if (nc_inq_type(ncid, NC_INT, name_in, &size_in)) ERR;
	 if (strcmp(name_in, "int") || size_in != sizeof(int)) ERR;
	 if (nc_inq_type(ncid, NC_FLOAT, name_in, &size_in)) ERR;
	 if (strcmp(name_in, "float") || size_in != sizeof(float)) ERR;
	 if (nc_inq_type(ncid, NC_DOUBLE, name_in, &size_in)) ERR;
	 if (strcmp(name_in, "double") || size_in != sizeof(double)) ERR;
	 if (nc_inq_type(ncid, NC_UBYTE, name_in, &size_in)) ERR;
	 if (strcmp(name_in, "ubyte") || size_in != sizeof(unsigned char)) ERR;
	 if (nc_inq_type(ncid, NC_USHORT, name_in, &size_in)) ERR;
	 if (strcmp(name_in, "ushort") || size_in != sizeof(unsigned short)) ERR;
	 if (nc_inq_type(ncid, NC_UINT, name_in, &size_in)) ERR;
	 if (strcmp(name_in, "uint") || size_in != sizeof(unsigned int)) ERR;
	 if (nc_inq_type(ncid, NC_INT64, name_in, &size_in)) ERR;
	 if (strcmp(name_in, "int64") || size_in != sizeof(long long)) ERR;
	 if (nc_inq_type(ncid, NC_UINT64, name_in, &size_in)) ERR;
	 if (strcmp(name_in, "uint64") || size_in != sizeof(unsigned long long)) ERR;
	 if (nc_inq_type(ncid, NC_STRING, name_in, &size_in)) ERR;
	 if (strcmp(name_in, "string") || size_in != 0) ERR;
	 if (xtype_in != NC_SHORT) ERR;
@end example

@node nc_inq_type, nc_inq_user_type, nc_inq_typeid, User Defined Data Types
@section Learn About a User Defined Type: nc_inq_type
@findex nc_inq_type

Given an ncid and a typeid, get the information about a type. This
function will work on any type, including atomic and any user defined
type, whether compound, opaque, enumeration, or variable length array.

For even more information about a user defined type @ref{nc_inq_user_type}.

@heading Usage 

@example
nc_inq_type(int ncid, nc_type xtype, char *name, size_t *sizep);
@end example

@table @code

@item ncid
The ncid for the group containing the type (ignored for atomic types).

@item xtype
The typeid for this type, as returned by nc_def_compound,
nc_def_opaque, nc_def_enum, nc_def_vlen, or nc_inq_var, or as found in
netcdf.h in the list of atomic types (NC_CHAR, NC_INT, etc.).

@item name
If non-NULL, the name of the user defined type will be copied here. It
will be NC_MAX_NAME bytes or less. For atomic types, the type name
from CDL will be given.

@item sizep
If non-NULL, the (in-memory) size of the type in bytes will be copied
here. VLEN type size is the size of nc_vlen_t. String size is returned
as the size of a character pointer. The size may be used to malloc
space for the data, no matter what the type.

@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad typeid.

@item NC_ENOTNC4
Seeking a user-defined type in a netCDF-3 file.

@item NC_ESTRICTNC3
Seeking a user-defined type in a netCDF-4 file for which classic model
has been turned on.

@item NC_EBADGRPID
Bad group ID in ncid.

@item NC_EBADID
Type ID not found.

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

This example is from the test program tst_enums.c, and it uses all the
possible inquiry functions on an enum type.

@example
      /* Check it out. */
      if (nc_inq_user_type(ncid, typeids[0], name_in, &base_size_in, &base_nc_type_in,
                           &nfields_in, &class_in)) ERR;
      if (strcmp(name_in, TYPE_NAME) || base_size_in != sizeof(int) ||
          base_nc_type_in != NC_INT || nfields_in != NUM_MEMBERS || class_in != NC_ENUM) ERR;
      if (nc_inq_type(ncid, typeids[0], name_in, &base_size_in)) ERR;
      if (strcmp(name_in, TYPE_NAME) || base_size_in != sizeof(int)) ERR;
      if (nc_inq_enum(ncid, typeids[0], name_in, &base_nc_type, &base_size_in, &num_members)) ERR;
      if (strcmp(name_in, TYPE_NAME) || base_nc_type != NC_INT || num_members != NUM_MEMBERS) ERR;
      for (i = 0; i < NUM_MEMBERS; i++)
      @{
         if (nc_inq_enum_member(ncid, typeid, i, name_in, &value_in)) ERR;
         if (strcmp(name_in, member_name[i]) || value_in != member_value[i]) ERR;
         if (nc_inq_enum_ident(ncid, typeid, member_value[i], name_in)) ERR;
         if (strcmp(name_in, member_name[i])) ERR;
      @}

      if (nc_close(ncid)) ERR; 
@end example

@node nc_inq_user_type, Compound Types, nc_inq_type, User Defined Data Types
@section Learn About a User Defined Type: nc_inq_user_type
@findex nc_inq_user_type

Given an ncid and a typeid, get the information about a user defined
type. This function will work on any user defined type, whether
compound, opaque, enumeration, or variable length array.

@heading Usage 

@example
nc_inq_user_type(int ncid, nc_type xtype, char *name, size_t *sizep, 
                 nc_type *base_nc_typep, size_t *nfieldsp, int *classp);
@end example

@table @code

@item ncid
The ncid for the group containing the user defined type.

@item xtype
The typeid for this type, as returned by nc_def_compound,
nc_def_opaque, nc_def_enum, nc_def_vlen, or nc_inq_var.

@item name
If non-NULL, the name of the user defined type will be copied here. It
will be NC_MAX_NAME bytes or less.

@item sizep
If non-NULL, the (in-memory) size of the type in bytes will be copied
here. VLEN type size is the size of nc_vlen_t. String size is returned
as the size of a character pointer. The size may be used to malloc
space for the data, no matter what the type.

@item nfieldsp
If non-NULL, the number of fields will be copied here for enum and
compound types.

@item classp
Return the class of the user defined type, NC_VLEN, NC_OPAQUE,
NC_ENUM, or NC_COMPOUND.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad typeid.

@item NC_EBADFIELDID
Bad fieldid.

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

@example
      /* Create a file. */
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;

      /* Create an enum type. */
      if (nc_def_enum(ncid, NC_INT, TYPE_NAME, &typeid)) ERR;
      for (i = 0; i < NUM_MEMBERS; i++)
         if (nc_insert_enum(ncid, typeid, member_name[i], 
                            &member_value[i])) ERR;

      /* Check it out. */
      if (nc_inq_user_type(ncid, typeid, name_in, &base_size_in, &base_nc_type_in,
                           &nfields_in, &class_in)) ERR;
      if (strcmp(name_in, TYPE_NAME) || base_size_in != sizeof(int) ||
          base_nc_type_in != NC_INT || nfields_in != NUM_MEMBERS || class_in != NC_ENUM) ERR;
@end example

@node Compound Types, nc_def_compound, nc_inq_user_type, User Defined Data Types
@section Compound Types Introduction
@cindex compound types, overview

Compound data types can be defined for netCDF-4/HDF5 format files. A 
compound datatype is similar to a struct in C and contains a collection 
of one or more atomic or user-defined types. The netCDF-4 compound data 
must comply with the properties and constraints of the HDF5 compound
data type in terms of which it is implemented.

In summary these are:
@itemize
@item
It has a fixed total size.
@item
It consists of zero or more named members that
do not overlap with other members.
@item
Each member has a name distinct from other members.
@item
Each member has its own datatype.
@item
Each member is referenced by an index number between zero and 
N-1, where N is the number of members in the compound datatype.
@item
Each member has a fixed byte offset, which is the first byte 
(smallest byte address) of that member in the compound datatype.
@item
In addition to other other user-defined data types or atomic
datatypes, a member can be a small fixed-size array of any type
with up to four fixed-size ``dimensions'' (not associated with named
netCDF dimensions). 
@end itemize

Currently there is an HDF5 restriction on total size of a
compound type to not larger than 2^16 = 65536 bytes. Attempts to
exceed this limit result in an NC_EHDFERR error.

Compound types are not supported in classic or 64-bit offset format
files. 

To write data in a compound type, first use nc_def_compound to create the
type, multiple calls to nc_insert_compound to add to the compound type, and
then write data with the appropriate nc_put_var1, nc_put_vara,
nc_put_vars, or nc_put_varm call.

To read data written in a compound type, you must know its
structure. Use the nc_inq_compound functions to learn about the compound
type.

@menu
* nc_def_compound::                  
* nc_insert_compound::               
* nc_inq_compound::                  
* nc_inq_compound_fieldname::        
* nc_inq_compound_fieldindex::       
* nc_inq_compound_fieldoffset::      
* nc_inq_compound_fieldtype::        
@end menu

@node nc_def_compound, nc_insert_compound, Compound Types, User Defined Data Types
@section Creating a Compound Type: nc_def_compound
@findex nc_def_compound

Create a compound type. Provide an ncid, a name, and a total size (in
bytes) of one element of the completed compound type.

After calling this function, fill out the type with repeated calls to
nc_insert_compound (@pxref{nc_insert_compound}). Call
nc_insert_compound once for each field you wish to insert into the
compound type.

Note that there does not seem to be a way to read such types into
structures in Fortran 90 (and there are no structures in Fortran 77).

@heading Usage 

@example
int nc_def_compound(int ncid, size_t size, const char *name, nc_type *typeidp);
@end example

@table @code

@item ncid
The groupid where this compound type will be created.

@item size
The size, in bytes, of the compound type. 

@item name
The name of the new compound type.

@item typeidp
A pointer to an nc_type. The typeid of the new type will be placed there.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENAMEINUSE
That name is in use.

@item NC_EMAXNAME
Name exceeds max length NC_MAX_NAME.

@item NC_EBADNAME
Name contains illegal characters.

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag NC_NETCDF4. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@item NC_EPERM
Attempt to write to a read-only file.

@item NC_ENOTINDEFINE
Not in define mode.

@end table

@heading Example

@example
      struct s1 
      @{
            int i1;
            int i2;
      @};
      struct s1 data[DIM_LEN], data_in[DIM_LEN];

      /* Create a file with a compound type. Write a little data. */
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
      if (nc_def_compound(ncid, sizeof(struct s1), SVC_REC, &typeid)) ERR;
      if (nc_insert_compound(ncid, typeid, BATTLES_WITH_KLINGONS, 
                             HOFFSET(struct s1, i1), NC_INT)) ERR;
      if (nc_insert_compound(ncid, typeid, DATES_WITH_ALIENS, 
                             HOFFSET(struct s1, i2), NC_INT)) ERR;
      if (nc_def_dim(ncid, STARDATE, DIM_LEN, &dimid)) ERR;
      if (nc_def_var(ncid, SERVICE_RECORD, typeid, 1, dimids, &varid)) ERR;
      if (nc_put_var(ncid, varid, data)) ERR;
      if (nc_close(ncid)) ERR;
@end example

@node nc_insert_compound, nc_insert_array_compound, nc_def_compound, User Defined Data Types
@section Inserting a Field into a Compound Type: nc_insert_compound
@findex nc_insert_compound

Insert a named field into a compound type.

@heading Usage 

@example
int nc_insert_compound(int ncid, nc_type typeid, const char *name, size_t offset, 
                       nc_type field_typeid);
@end example

@table @code

@item ncid
The groupid where a field for this compound type will be inserted.

@item typeid
The typeid for this compound type, as returned by nc_def_compound, or
nc_inq_var.

@item name
The name of the new field.

@item offset
Offset in byte from the beginning of the compound type for this
field.

@item field_typeid
The type of the field to be inserted.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENAMEINUSE
That name is in use. Field names must be unique within a compound type.

@item NC_EMAXNAME
Name exceed max length NC_MAX_NAME.

@item NC_EBADNAME
Name contains illegal characters.

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag NC_NETCDF4. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@item NC_ENOTINDEFINE
Not in define mode.

@end table

@heading Example

@example
@end example

@node nc_insert_array_compound, nc_inq_compound, nc_insert_compound, User Defined Data Types
@section Inserting an Array Field into a Compound Type: nc_insert_array_compound
@findex nc_insert_array_compound

Insert a named field into a compound type.

@heading Usage 

@example
int nc_insert_array_compound(int ncid, nc_type xtype, const char *name, 
                         size_t offset, nc_type field_typeid,
                         int ndims, const int *dim_sizes);
@end example

@table @code

@item ncid
The ID of the file that contains the array type and the compound type.

@item xtype
The typeid for this compound type, as returned by nc_def_compound, or
nc_inq_var.

@item name
The name of the new field.

@item offset
Offset in byte from the beginning of the compound type for this
field.

@item field_typeid
The base type of the array to be inserted.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENAMEINUSE
That name is in use. Field names must be unique within a compound type.

@item NC_EMAXNAME
Name exceed max length NC_MAX_NAME.

@item NC_EBADNAME
Name contains illegal characters.

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag NC_NETCDF4. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@item NC_ENOTINDEFINE
Not in define mode.

@item NC_ETYPEDEFINED
Attempt to change type that has already been committed. The first time
the file leaves define mode, all defined types are committed, and
can't be changed. If you wish to add an array to a compound type, you
must do so before the compound type is committed.

@end table

@heading Example

This example comes from the test file libsrc4/tst_compounds.c, which
writes data about some Star Fleet officers who are known to use netCDF
data. 

@example
   /* Since some aliens exists in different, or more than one,
    * dimensions, StarFleet keeps track of the dimensional abilities
    * of everyone on 7 dimensions. */
#define NUM_DIMENSIONS 7
   struct dim_rec
   @{
         int starfleet_id;
         int abilities[NUM_DIMENSIONS];
   @};
   struct dim_rec dim_data_out[DIM_LEN], dim_data_in[DIM_LEN];
   
   /* Create some phoney data. */   
   for (i=0; i<DIM_LEN; i++)
   @{
      /* snip */
      /* Dimensional data. */
      dim_data_out[i].starfleet_id = i;
      for (j = 0; j < NUM_DIMENSIONS; j++)
         dim_data_out[i].abilities[j] = j;
      /* snip */
   @}

   printf("*** testing compound variable containing an array of ints...");
   @{
      nc_type field_typeid;
      int dim_sizes[] = @{NUM_DIMENSIONS@};

      /* Create a file with a compound type which contains an array of
       * int. Write a little data. */
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
      if (nc_def_compound(ncid, sizeof(struct dim_rec), "SFDimRec", &typeid)) ERR;
      if (nc_insert_compound(ncid, typeid, "starfleet_id", 
                             HOFFSET(struct dim_rec, starfleet_id), NC_INT)) ERR;
      if (nc_insert_array_compound(ncid, typeid, "abilities", 
                             HOFFSET(struct dim_rec, abilities), NC_INT, 1, dim_sizes)) ERR;
      if (nc_inq_compound_field(ncid, xtype, 1, name, &offset, &field_typeid, 
                                &field_ndims, field_sizes)) ERR;
      if (strcmp(name, "abilities") || offset != 4 || field_typeid != NC_INT || 
          field_ndims != 1 || field_sizes[0] != dim_sizes[0]) ERR;
      if (nc_def_dim(ncid, STARDATE, DIM_LEN, &dimid)) ERR;
      if (nc_def_var(ncid, "dimension_data", typeid, 1, dimids, &varid)) ERR;
      if (nc_put_var(ncid, varid, dim_data_out)) ERR;
      if (nc_close(ncid)) ERR;

      /* Open the file and take a look. */
      if (nc_open(FILE_NAME, NC_WRITE, &ncid)) ERR;
      if (nc_inq_var(ncid, 0, name, &xtype, &ndims, dimids, &natts)) ERR;
      if (strcmp(name, "dimension_data") || ndims != 1 || natts != 0 || dimids[0] != 0) ERR;
      if (nc_inq_compound(ncid, xtype, name, &size, &nfields)) ERR;
      if (nfields != 2 || size != sizeof(struct dim_rec) || strcmp(name, "SFDimRec")) ERR;
      if (nc_inq_compound_field(ncid, xtype, 1, name, &offset, &field_typeid, 
                                &field_ndims, field_sizes)) ERR;
      if (strcmp(name, "abilities") || offset != 4 || field_typeid != NC_INT || 
          field_ndims != 1 || field_sizes[0] != NUM_DIMENSIONS) ERR;
      if (nc_get_var(ncid, varid, dim_data_in)) ERR;
      for (i=0; i<DIM_LEN; i++)
      @{
         if (dim_data_in[i].starfleet_id != dim_data_out[i].starfleet_id) ERR;
         for (j = 0; j < NUM_DIMENSIONS; j++)
            if (dim_data_in[i].abilities[j] != dim_data_out[i].abilities[j]) ERR;
      @}
      if (nc_close(ncid)) ERR;
   @}
@end example

@node nc_inq_compound, nc_inq_compound_name, nc_insert_array_compound, User Defined Data Types
@section Learn About a Compound Type: nc_inq_compound
@findex nc_inq_compound

Get the number of fields, len, and name of a compound type.

@heading Usage 

@example
int nc_inq_compound(int ncid, nc_type xtype, char *name, size_t *sizep, 
                    size_t *nfieldsp);
@end example

@table @code

@item ncid
The ID of any group in the file that contains the compound type.

@item xtype
The typeid for this compound type, as returned by nc_def_compound, or
nc_inq_var.

@item name
Pointer to an already allocated char array which will get the name, as
a null terminated string. It will have a maximum length of
NC_MAX_NAME + 1. Ignored if NULL.

@item sizep
A pointer to a size_t. The size of the compound type will be put
here. Ignored if NULL.

@item nfieldsp
A pointer to a size_t. The number of fields in the compound type will
be placed here. Ignored if NULL.

@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Couldn't find this ncid.

@item NC_ENOTNC4
Not a netCDF-4/HDF5 file.

@item NC_ESTRICTNC3
A netCDF-4/HDF5 file, but with CLASSIC_MODEL. No user defined types
are allowed in the classic model.

@item NC_EBADTYPE
This type not a compound type.

@item NC_EBADTYPEID
Bad type id. 

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

The following example is from the test program
libsrc4/tst_compounds.c. See also the example for
@xref{nc_insert_array_compound}.

@example
#define BATTLES_WITH_KLINGONS "Number_of_Battles_with_Klingons"
#define DATES_WITH_ALIENS "Dates_with_Alien_Hotties"

   struct s1 
   @{
         int i1;
         int i2;
   @};

   /* Create a file with a compound type. */
   if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
   if (nc_def_compound(ncid, sizeof(struct s1), SVC_REC, &typeid)) ERR;
   if (nc_inq_compound(ncid, typeid, name, &size, &nfields)) ERR;
   if (nfields) ERR;
   if (nc_insert_compound(ncid, typeid, BATTLES_WITH_KLINGONS, 
                     HOFFSET(struct s1, i1), NC_INT)) ERR;
   if (nc_insert_compound(ncid, typeid, DATES_WITH_ALIENS, 
                     HOFFSET(struct s1, i2), NC_INT)) ERR;

   /* Check the compound type. */                             
   if (nc_inq_compound(ncid, xtype, name, &size, &nfields)) ERR;
   if (nfields != 2 || size != 8 || strcmp(name, SVC_REC)) ERR;
   if (nc_inq_compound_name(ncid, xtype, name)) ERR;
   if (strcmp(name, SVC_REC)) ERR;
   if (nc_inq_compound_size(ncid, xtype, &size)) ERR;
   if (size != 8) ERR;
   if (nc_inq_compound_nfields(ncid, xtype, &nfields)) ERR;
   if (nfields != 2) ERR;
   if (nc_inq_compound_field(ncid, xtype, 0, name, &offset, &field_xtype, &field_ndims, field_sizes)) ERR;
   if (strcmp(name, BATTLES_WITH_KLINGONS) || offset != 0 || (field_xtype != NC_INT || field_ndims != 0)) ERR;
   if (nc_inq_compound_field(ncid, xtype, 1, name, &offset, &field_xtype, &field_ndims, field_sizes)) ERR;
   if (strcmp(name, DATES_WITH_ALIENS) || offset != 4 || field_xtype != NC_INT) ERR;
   if (nc_inq_compound_fieldname(ncid, xtype, 1, name)) ERR;
   if (strcmp(name, DATES_WITH_ALIENS)) ERR;
   if (nc_inq_compound_fieldindex(ncid, xtype, BATTLES_WITH_KLINGONS, &fieldid)) ERR;
   if (fieldid != 0) ERR;
   if (nc_inq_compound_fieldoffset(ncid, xtype, 1, &offset)) ERR;
   if (offset != 4) ERR;
   if (nc_inq_compound_fieldtype(ncid, xtype, 1, &field_xtype)) ERR;
   if (field_xtype != NC_INT) ERR;
@end example

@node nc_inq_compound_name, nc_inq_compound_size, nc_inq_compound, User Defined Data Types
@section Learn the Name of a Compound Type: nc_inq_compound_name
@findex nc_inq_compound_name

Get the name of a compound type.

@heading Usage 

@example
int nc_inq_compound_name(int ncid, nc_type xtype, char *name);
@end example

@table @code

@item ncid
The groupid where this compound type exists.

@item xtype
The typeid for this compound type.

@item name
Pointer to an already allocated char array which will get the name, as
a null terminated string. It will have a maximum length of
NC_MAX_NAME+1.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad type id. 

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

See the example section for @ref{nc_inq_compound}.

@node nc_inq_compound_size, nc_inq_compound_nfields, nc_inq_compound_name, User Defined Data Types
@section Learn the Size of a Compound Type: nc_inq_compound_size
@findex nc_inq_compound_size

Get the len of a compound type.

@heading Usage 

@example
int nc_inq_compound_size(int ncid, nc_type xtype, size_t *sizep);
@end example

@table @code

@item ncid
The groupid where this compound type exists.

@item xtype
The typeid for this compound type.

@item size
A pointer, which, if not NULL, get the size of the compound type.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad type id. 

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

See the example section for @ref{nc_inq_compound}.

@node nc_inq_compound_nfields, nc_inq_compound_field, nc_inq_compound_size, User Defined Data Types
@section Learn the Number of Fields in a Compound Type: nc_inq_compound_nfields
@findex nc_inq_compound_nfields

Get the number of fields of a compound type.

@heading Usage 

@example
nc_inq_compound_nfields(int ncid, nc_type xtype, size_t *nfieldsp);
@end example

@table @code

@item ncid
The groupid where this compound type exists.

@item xtype
The typeid for this compound type.

@item nfieldsp
A pointer, which, if not NULL, get the number of fields of the
compound type.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad type id. 

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

See the example section for @ref{nc_inq_compound}.

@node nc_inq_compound_field, nc_inq_compound_fieldname, nc_inq_compound_nfields, User Defined Data Types
@section Learn About a Field of a Compound Type: nc_inq_compound_field
@findex nc_inq_compound_field

Get information about one of the fields of a compound type.

@heading Usage 

@example
int nc_inq_compound_field(int ncid, nc_type xtype, int fieldid, char *name, 
                      size_t *offsetp, nc_type *field_typeidp, int *ndimsp, 
                      int *dim_sizesp);
@end example

@table @code

@item ncid
The groupid where this compound type exists.

@item xtype
The typeid for this compound type, as returned by nc_def_compound, or
nc_inq_var.

@item fieldid
A zero-based index number specifying a field in the compound type.

@item name
A pointer which, if non-NULL, will get the name of the field.

@item offsetp
A pointer which, if non-NULL, will get the offset of the field.

@item field_typeid
A pointer which, if non-NULL, will get the typeid of the field.

@item ndimsp
A pointer which, if non-NULL, will get the number of dimensions of the field.

@item dim_sizesp
A pointer which, if non-NULL, will get the dimension sizes of the field.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad type id. 

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

See the example section for @ref{nc_inq_compound}.

@node nc_inq_compound_fieldname, nc_inq_compound_fieldindex, nc_inq_compound_field, User Defined Data Types
@section Find the Name of a Field in a Compound Type: nc_inq_compound_fieldname
@findex nc_inq_compound_fieldname

Given the typeid and the fieldid, get the name.

@heading Usage 

@example
int nc_inq_compound_fieldname(nc_type typeid, int fieldid, char *name);
@end example

@table @code

@item typeid
The typeid for this compound type, as returned by nc_def_compound, or
nc_inq_var.

@item fieldid
The id of the field in the compound type. Fields are numbered starting
with 0 for the first inserted field.

@item name
Pointer to an already allocated char array which will get the name, as
a null terminated string. It will have a maximum length of
NC_MAX_NAME+1.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad type id. 

@item NC_EBADFIELDID
Bad field id. 

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

See the example section for @ref{nc_inq_compound}.

@node  nc_inq_compound_fieldindex, nc_inq_compound_fieldoffset, nc_inq_compound_fieldname, User Defined Data Types
@section Get the FieldID of a Compound Type Field: nc_inq_compound_fieldindex
@findex nc_inq_compound_fieldindex

Given the typeid and the name, get the fieldid. 

@heading Usage 

@example
int nc_inq_compound_fieldindex(nc_type typeid, const char *name, int *fieldidp);
@end example

@table @code

@item typeid
The typeid for this compound type, as returned by nc_def_compound, or
nc_inq_var.

@item name
The name of the field.

@item fieldidp
A pointer to an int which will get the field id of the named field.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad type id. 

@item NC_EUNKNAME
Can't find field of this name.

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

See the example section for @ref{nc_inq_compound}.

@node nc_inq_compound_fieldoffset, nc_inq_compound_fieldtype, nc_inq_compound_fieldindex, User Defined Data Types
@section Get the Offset of a Field: nc_inq_compound_fieldoffset
@findex nc_inq_compound_fieldoffset

Given the typeid and fieldid, get the offset.

@heading Usage 

@example
int nc_inq_compound_fieldoffset(nc_type typeid, int fieldid, 
                                size_t *offsetp); 
@end example

@table @code

@item typeid
The typeid for this compound type, as returned by nc_def_compound, or
nc_inq_var.

@item fieldid
The id of the field in the compound type. Fields are numbered starting
with 0 for the first inserted field.

@item offsetp
A pointer to a size_t. The offset of the field will be placed there.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad typeid.

@item NC_EBADFIELDID
Bad fieldid.

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

See the example section for @ref{nc_inq_compound}.

@node nc_inq_compound_fieldtype, nc_inq_compound_fieldndims, nc_inq_compound_fieldoffset, User Defined Data Types
@section Find the Type of a Field: nc_inq_compound_fieldtype
@findex nc_inq_compound_fieldtype

Given the typeid and the fieldid, get the type of that field. 

@heading Usage 

@example
nc_inq_compound_fieldtype(nc_type typeid, int fieldid, nc_type *field_typeidp);
@end example

@table @code

@item typeid
The typeid for this compound type, as returned by nc_def_compound, or
nc_inq_var.

@item fieldid
The id of the field in the compound type. Fields are numbered starting
with 0 for the first inserted field.

@item field_typeidp
Pointer to a nc_type which will get the typeid of the field.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad typeid.

@item NC_EBADFIELDID
Bad fieldid.

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

See the example section for @ref{nc_inq_compound}.

@node nc_inq_compound_fieldndims, nc_inq_compound_fielddim_sizes, nc_inq_compound_fieldtype, User Defined Data Types
@section Find the Number of Dimensions in an Array Field: nc_inq_compound_fieldndims
@findex nc_inq_compound_fieldndims

Given the typeid and the fieldid, get the number of dimensions of that
field.

@heading Usage 

@example
int nc_inq_compound_fieldndims(int ncid, nc_type xtype, int fieldid, 
                               int *ndimsp);
@end example

@table @code

@item ncid
The file or group ID.

@item xtype
The typeid for this compound type, as returned by nc_def_compound, or
nc_inq_var.

@item fieldid
The id of the field in the compound type. Fields are numbered starting
with 0 for the first inserted field.

@item ndimsp
Pointer to an int which will get the number of dimensions of the
field. Non-array fields have 0 dimensions.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad typeid.

@item NC_EBADFIELDID
Bad fieldid.

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

See the example section for @ref{nc_inq_compound}.

@node nc_inq_compound_fielddim_sizes, Variable Length Array, nc_inq_compound_fieldndims, User Defined Data Types
@section Find the Sizes of Dimensions in an Array Field: nc_inq_compound_fielddim_sizes
@findex nc_inq_compound_fielddim_sizes

Given the xtype and the fieldid, get the sizes of dimensions for
that field. User must have allocated storage for the dim_sizes.

@heading Usage 

@example
int nc_inq_compound_fielddim_sizes(int ncid, nc_type xtype, int fieldid, 
                                   int *dim_sizes);
@end example

@table @code

@item ncid
The file or group ID.

@item xtype
The typeid for this compound type, as returned by nc_def_compound, or
nc_inq_var.

@item fieldid
The id of the field in the compound type. Fields are numbered starting
with 0 for the first inserted field.

@item dim_sizesp
Pointer to an array of int which will get the sizes of the dimensions
of the field. Non-array fields have 0 dimensions.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad typeid.

@item NC_EBADFIELDID
Bad fieldid.

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

See the example section for @ref{nc_inq_compound}.

@node Variable Length Array, nc_def_vlen, nc_inq_compound_fielddim_sizes, User Defined Data Types
@section Variable Length Array Introduction
@cindex variable length arrays
@cindex VLEN

NetCDF-4 added support for a variable length array type. This is not
supported in classic or 64-bit offset files, or in netCDF-4 files
which were created with the NC_CLASSIC_MODEL flag.

A variable length array is represented in C as a structure from HDF5,
the nc_vlen_t structure. It contains a len member, which contains the
length of that array, and a pointer to the array.

So an array of VLEN in C is an array of nc_vlen_t structures.

VLEN arrays are handled differently with respect to allocation of
memory. Generally, when reading data, it is up to the user to malloc
(and subsequently free) the memory needed to hold the data. It is up to
the user to ensure that enough memory is allocated.

With VLENs, this is impossible. The user cannot know the size of an
array of VLEN until after reading the array. Therefore when reading
VLEN arrays, the netCDF library will allocate the memory for the data within
each VLEN.

It is up to the user, however, to eventually free this memory. This is
not just a matter of one call to free, with the pointer to the array
of VLENs; each VLEN contains a pointer which must be freed.

When dynamically allocating space to hold an array of VLEN, allocate
storage for an array of nc_vlen_t. 

Compression is permitted but may not be effective for VLEN data,
because the compression is applied to the nc_vlen_t structs, rather
than the actual data.

@node nc_def_vlen, nc_inq_vlen, Variable Length Array, User Defined Data Types
@section Define a Variable Length Array (VLEN): nc_def_vlen
@findex nc_def_vlen
@cindex VLEN, defining

Use this function to define a variable length array type. 

@heading Usage

@example
nc_def_vlen(int ncid, const char *name, nc_type base_typeid, nc_type *xtypep);
@end example

@table @code

@item ncid
The ncid of the file to create the VLEN type in.

@item name 
A name for the VLEN type.

@item base_typeid
The typeid of the base type of the VLEN. For example, for a VLEN of
shorts, the base type is NC_SHORT. This can be a user defined type.

@item xtypep
A pointer to an nc_type variable. The typeid of the new VLEN type will
be set here.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EMAXNAME
NC_MAX_NAME exceeded.

@item NC_ENAMEINUSE
Name is already in use.

@item NC_EBADNAME
Attribute or variable name contains illegal characters.

@item NC_EBADID
ncid invalid.

@item NC_EBADGRPID
Group ID part of ncid was invalid.

@item NC_EINVAL
Size is invalid.

@item NC_ENOMEM
Out of memory.

@end table

@heading Example

@example
#define DIM_LEN 3
#define ATT_NAME "att_name"

   nc_vlen_t data[DIM_LEN];
   int *phony;

   /* Create phony data. */
   for (i=0; i<DIM_LEN; i++)
   @{
      if (!(phony = malloc(sizeof(int) * i+1)))
         return NC_ENOMEM;
      for (j=0; j<i+1; j++)
         phony[j] = -99;
      data[i].p = phony;
      data[i].len = i+1;
   @}

      /* Define a VLEN of NC_INT, and write an attribute of that
      type. */
      if (nc_def_vlen(ncid, "name1", NC_INT, &typeid)) ERR;
      if (nc_put_att(ncid, NC_GLOBAL, ATT_NAME, typeid, DIM_LEN, data)) ERR;
@end example

@node nc_inq_vlen, nc_free_vlen, nc_def_vlen, User Defined Data Types
@section Learning about a Variable Length Array (VLEN) Type: nc_inq_vlen
@findex nc_def_vlen
@cindex VLEN, defining

Use this type to learn about a vlen.

@heading Usage

@example
nc_inq_vlen(int ncid, nc_type xtype, char *name, size_t *datum_sizep, 
            nc_type *base_nc_typep);
@end example

@table @code

@item ncid
The ncid of the file that contains the VLEN type.

@item xtype
The type of the VLEN to inquire about.

@item name
A pointer for storage for the types name. The name will be NC_MAX_NAME
characters or less.

@item datum_sizep
A pointer to a size_t, this will get the size of one element of this
vlen.

@item base_nc_typep
A pointer to an nc_type, this will get the type of the VLEN base
type. (In other words, what type is this a VLEN of?)

@end table


@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPE
Can't find the typeid.

@item NC_EBADID
ncid invalid.

@item NC_EBADGRPID
Group ID part of ncid was invalid.

@end table

@heading Example

@example
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
      if (nc_def_vlen(ncid, "name1", NC_INT, &typeid)) ERR;
      if (nc_inq_vlen(ncid, typeid, name_in, &size_in, &base_nc_type_in)) ERR;
      if (base_nc_type_in != NC_INT || (size_in != sizeof(int) || strcmp(name_in, VLEN_NAME))) ERR;
      if (nc_inq_user_type(ncid, typeid, name_in, &size_in, &base_nc_type_in, NULL, &class_in)) ERR;
      if (base_nc_type_in != NC_INT || (size_in != sizeof(int) || strcmp(name_in, VLEN_NAME))) ERR;
      if (nc_inq_compound(ncid, typeid, name_in, &size_in, NULL) != NC_EBADTYPE) ERR;
      if (nc_put_att(ncid, NC_GLOBAL, ATT_NAME, typeid, DIM_LEN, data)) ERR;
      if (nc_close(ncid)) ERR;
@end example

@node nc_free_vlen, nc_free_vlens, nc_inq_vlen, User Defined Data Types
@section Releasing Memory for a Variable Length Array (VLEN) Type: nc_free_vlen
@findex nc_free_vlen
@cindex VLEN, defining

When a VLEN is read into user memory from the file, the HDF5 library
performs memory allocations for each of the variable length arrays
contained within the VLEN structure. This memory must be freed by the
user to avoid memory leaks.

This violates the normal netCDF expectation that the user is
responsible for all memory allocation. But, with VLEN arrays, the
underlying HDF5 library allocates the memory for the user, and the user
is responsible for deallocating that memory.

To save the user the trouble calling free() on each element of the
VLEN array (i.e. the array of arrays), the nc_free_vlen function is
provided.

@heading Usage

@example
int nc_free_vlen(nc_vlen_t *vl);
@end example

@table @code

@item vl
A pointer to the variable length array structure which is to be freed.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPE
Can't find the typeid.

@end table

@heading Example

This example is from test program libsrc4/tst_vl.c.

@example
   /* Free the memory used in our phony data. */
   for (i=0; i<DIM_LEN; i++)
      if (nc_free_vlen(&data[i])) ERR;
@end example

@node nc_free_vlens, Opaque Type, nc_free_vlen, User Defined Data Types
@section Releasing Memory for an Array of Variable Length Array (VLEN) Type: nc_free_vlen
@findex nc_free_vlen
@cindex VLEN, defining

When a VLEN is read into user memory from the file, the HDF5 library
performs memory allocations for each of the variable length arrays
contained within the VLEN structure. This memory must be freed by the
user to avoid memory leaks.

This violates the normal netCDF expectation that the user is
responsible for all memory allocation. But, with VLEN arrays, the
underlying HDF5 library allocates the memory for the user, and the user
is responsible for deallocating that memory.

To save the user the trouble calling free() on each element of the
VLEN array (i.e. the array of arrays), the nc_free_vlens function is
provided. It frees all the vlens in an array.

@heading Usage

@example
int nc_free_vlens(size_t len, nc_vlen_t vlens[])
@end example

@table @code

@item len
Length of the VLEN array to be freed.

@item vlens
Array of VLENs to be freed.

@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@end table

@node Opaque Type, nc_def_opaque, nc_free_vlens, User Defined Data Types
@section Opaque Type Introduction
@cindex opaque type

NetCDF-4 added support for the opaque type. This is not supported in
classic or 64-bit offset files.

The opaque type is a type which is a collection of objects of a known
size. (And each object is the same size). Nothing is known to netCDF
about the contents of these blobs of data, except their size in bytes,
and the name of the type.

To use an opaque type, first define it with @ref{nc_def_opaque}. If
encountering an enum type in a new data file, use @ref{nc_inq_opaque}
to learn its name and size.

@node nc_def_opaque, nc_inq_opaque, Opaque Type, User Defined Data Types
@section Creating Opaque Types: nc_def_opaque
@findex nc_def_opaque

Create an opaque type. Provide a size and a name.

@heading Usage 

@example
nc_def_opaque(int ncid, size_t size, const char *name, nc_type *typeidp);
@end example

@table @code

@item ncid
The groupid where the type will be created. The type may be used
anywhere in the file, no matter what group it is in.

@item size
The size of each opaque object.

@item name
The name for this type. Must be shorter than NC_MAX_NAME.

@item typeidp
Pointer where the new typeid for this type is returned. Use this
typeid when defining variables of this type with @ref{nc_def_var}.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad typeid.

@item NC_EBADFIELDID
Bad fieldid.

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

This example is from the test program libsrc4/tst_opaques.c.

@example
      /* Create a file that has an opaque attribute. */
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
      if (nc_def_opaque(ncid, BASE_SIZE, TYPE_NAME, &xtype)) ERR;
@end example

@node nc_inq_opaque, Enum Type, nc_def_opaque, User Defined Data Types
@section Learn About an Opaque Type: nc_inq_opaque
@findex nc_inq_opaque

Given a typeid, get the information about an opaque type.

@heading Usage 

@example
int nc_inq_opaque(int ncid, nc_type xtype, char *name, size_t *sizep);
@end example

@table @code

@item ncid
The ncid for the group containing the opaque type.

@item xtype
The typeid for this opaque type, as returned by nc_def_compound, or
nc_inq_var.

@item name
If non-NULL, the name of the opaque type will be copied here. It will
be NC_MAX_NAME bytes or less.

@item sizep
If non-NULL, the size of the opaque type will be copied here.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad typeid.

@item NC_EBADFIELDID
Bad fieldid.

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

This example is from test program libsrc4/tst_opaques.c:

@example
      if (nc_def_opaque(ncid, BASE_SIZE, TYPE_NAME, &xtype)) ERR;

      if (nc_inq_opaque(ncid, xtype, name_in, &base_size_in)) ERR;
      if (strcmp(name_in, TYPE_NAME) || base_size_in != BASE_SIZE) ERR;
@end example

@node Enum Type, nc_def_enum, nc_inq_opaque, User Defined Data Types
@section Enum Type Introduction
@cindex enum type

NetCDF-4 added support for the enum type. This is not supported in
classic or 64-bit offset files.

@node nc_def_enum, nc_insert_enum, Enum Type, User Defined Data Types
@section Creating a Enum Type: nc_def_enum
@findex nc_def_enum

Create an enum type. Provide an ncid, a name, and a base integer
type. 

After calling this function, fill out the type with repeated calls to
nc_insert_enum (@pxref{nc_insert_enum}). Call nc_insert_enum once for
each value you wish to make part of the enumeration.

@heading Usage 

@example
int nc_def_enum(int ncid, nc_type base_typeid, const char *name, 
                nc_type *typeidp);
@end example

@table @code

@item ncid
The groupid where this compound type will be created.

@item base_typeid
The base integer type for this enum. Must be one of: NC_BYTE,
NC_UBYTE, NC_SHORT, NC_USHORT, NC_INT, NC_UINT, NC_INT64, NC_UINT64.

@item name
The name of the new enum type.

@item typeidp
A pointer to an nc_type. The typeid of the new type will be placed
there.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENAMEINUSE
That name is in use.

@item NC_EMAXNAME
Name exceeds max length NC_MAX_NAME.

@item NC_EBADNAME
Name contains illegal characters.

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag NC_NETCDF4. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@item NC_EPERM
Attempt to write to a read-only file.

@item NC_ENOTINDEFINE
Not in define mode.

@end table

The following example, from libsrc4/tst_enums.c, shows the creation
and use of an enum type, including the use of a fill value.

@example
       int dimid, varid;
       size_t num_members_in;
       int class_in;
       unsigned char value_in;

       enum clouds @{           /* a C enumeration */
           CLEAR=0,
           CUMULONIMBUS=1,
           STRATUS=2,
           STRATOCUMULUS=3,
           CUMULUS=4,
           ALTOSTRATUS=5,
           NIMBOSTRATUS=6,
           ALTOCUMULUS=7,
           CIRROSTRATUS=8,
           CIRROCUMULUS=9,
           CIRRUS=10,
           MISSING=255@};

       struct @{
           char *name;
           unsigned char value;
       @} cloud_types[] = @{
           @{"Clear", CLEAR@}, 
           @{"Cumulonimbus", CUMULONIMBUS@}, 
           @{"Stratus", STRATUS@}, 
           @{"Stratocumulus", STRATOCUMULUS@}, 
           @{"Cumulus", CUMULUS@}, 
           @{"Altostratus", ALTOSTRATUS@}, 
           @{"Nimbostratus", NIMBOSTRATUS@}, 
           @{"Altocumulus", ALTOCUMULUS@}, 
           @{"Cirrostratus", CIRROSTRATUS@}, 
           @{"Cirrocumulus", CIRROCUMULUS@}, 
           @{"Cirrus", CIRRUS@}, 
           @{"Missing", MISSING@}
       @};
       int var_dims[VAR2_RANK];
       unsigned char att_val;
       unsigned char cloud_data[DIM2_LEN] = @{
           CLEAR, STRATUS, CLEAR, CUMULONIMBUS, MISSING@};
       unsigned char cloud_data_in[DIM2_LEN];

       if (nc_create(FILE_NAME, NC_CLOBBER | NC_NETCDF4, &ncid)) ERR;

       /* Create an enum type. */
       if (nc_def_enum(ncid, NC_UBYTE, TYPE2_NAME, &typeid)) ERR;
       num_members = (sizeof cloud_types) / (sizeof cloud_types[0]);
       for (i = 0; i < num_members; i++)
           if (nc_insert_enum(ncid, typeid, cloud_types[i].name,
                              &cloud_types[i].value)) ERR;

       /* Declare a station dimension */
       if (nc_def_dim(ncid, DIM2_NAME, DIM2_LEN, &dimid)) ERR;
       /* Declare a variable of the enum type */
       var_dims[0] = dimid;
       if (nc_def_var(ncid, VAR2_NAME, typeid, VAR2_RANK, var_dims, &varid)) ERR;
       /* Create and write a variable attribute of the enum type */
       att_val = MISSING;
       if (nc_put_att(ncid, varid, ATT2_NAME, typeid, ATT2_LEN, &att_val)) ERR;
       if (nc_enddef(ncid)) ERR;
       /* Store some data of the enum type */
       if(nc_put_var(ncid, varid, cloud_data)) ERR;
       /* Write the file. */
       if (nc_close(ncid)) ERR;

@end example

@node nc_insert_enum, nc_inq_enum, nc_def_enum, User Defined Data Types
@section Inserting a Field into a Enum Type: nc_insert_enum
@findex nc_insert_enum

Insert a named member into a enum type.

@heading Usage 

@example
int nc_insert_enum(int ncid, nc_type xtype, const char *identifier, 
                   const void *value);
@end example

@table @code

@item ncid
The ncid of the group which contains the type.

@item typeid
The typeid for this enum type, as returned by nc_def_enum, or
nc_inq_var.

@item identifier
The identifier of the new member.

@item value
The value that is to be associated with this member.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad group id. 

@item NC_ENAMEINUSE
That name is in use. Field names must be unique within a enum type.

@item NC_EMAXNAME
Name exceed max length NC_MAX_NAME.

@item NC_EBADNAME
Name contains illegal characters.

@item NC_ENOTNC4
Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4
operations can only be performed on files defined with a create mode
which includes flag NC_NETCDF4. (@pxref{nc_open}).

@item NC_ESTRICTNC3
This file was created with the strict netcdf-3 flag, therefore
netcdf-4 operations are not allowed. (@pxref{nc_open}).

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@item NC_ENOTINDEFINE
Not in define mode.

@end table

@heading Example

This example is from libsrc4/tst_enums.c; also see the example in @xref{nc_def_enum}.

@example
      char brady_name[NUM_BRADYS][NC_MAX_NAME + 1] = @{"Mike", "Carol", "Greg", "Marsha",
                                                       "Peter", "Jan", "Bobby", "Whats-her-face",
                                                       "Alice"@};
      unsigned char brady_value[NUM_BRADYS] = @{0, 1,2,3,4,5,6,7,8@};
      unsigned char data[BRADY_DIM_LEN] = @{0, 4, 8@};
      unsigned char value_in;

      /* Create a file. */
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;

      /* Create an enum type based on unsigned bytes. */
      if (nc_def_enum(ncid, NC_UBYTE, BRADYS, &typeid)) ERR;
      for (i = 0; i < NUM_BRADYS; i++)
         if (nc_insert_enum(ncid, typeid, brady_name[i], 
                            &brady_value[i])) ERR;

@end example

@node nc_inq_enum, nc_inq_enum_member, nc_insert_enum, User Defined Data Types
@section Learn About a Enum Type: nc_inq_enum
@findex nc_inq_enum

Get information about a user-define enumeration type.

@heading Usage 

@example
nc_inq_enum(int ncid, nc_type xtype, char *name, nc_type *base_nc_typep, 
            size_t *base_sizep, size_t *num_membersp);
@end example

@table @code

@item ncid
The group ID of the group which holds the enum type.

@item xtype
The typeid for this enum type, as returned by nc_def_enum, or
nc_inq_var.

@item name
Pointer to an already allocated char array which will get the name, as
a null terminated string. It will have a maximum length of
NC_MAX_NAME+1.

@item base_nc_typep
If non-NULL, a pointer to a nc_type, which will get the base integer
type of this enum.

@item base_sizep
If non-NULL, a size_t pointer, which will get the size (in bytes) of
the base integer type of this enum.

@item num_membersp
If non-NULL, a size_t pointer which will get the number of members
defined for this enumeration type.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad type id. 

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

This example is from libsrc4/tst_enums.c, and is a continuation of the
example above for nc_insert_enum. First an enum type is created, with
one element for each of the nine members of the Brady family on a
popular American television show which occupies far too much memory
space in my brain!

In the example, the enum type is created, then checked using the
nc_inq_enum and nc_inq_enum_member functions. See @ref{nc_inq_enum_member}.

@example
      char brady_name[NUM_BRADYS][NC_MAX_NAME + 1] = @{"Mike", "Carol", "Greg", "Marsha",
                                                       "Peter", "Jan", "Bobby", "Whats-her-face",
                                                       "Alice"@};
      unsigned char brady_value[NUM_BRADYS] = @{0, 1,2,3,4,5,6,7,8@};
      unsigned char data[BRADY_DIM_LEN] = @{0, 4, 8@};
      unsigned char value_in;

      /* Create a file. */
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;

      /* Create an enum type based on unsigned bytes. */
      if (nc_def_enum(ncid, NC_UBYTE, BRADYS, &typeid)) ERR;
      for (i = 0; i < NUM_BRADYS; i++)
         if (nc_insert_enum(ncid, typeid, brady_name[i], 
                            &brady_value[i])) ERR;

      /* Check it out. */
      if (nc_inq_enum(ncid, typeid, name_in, &base_nc_type, &base_size_in, &num_members)) ERR;
      if (strcmp(name_in, BRADYS) || base_nc_type != NC_UBYTE || base_size_in != 1 ||
          num_members != NUM_BRADYS) ERR;
      for (i = 0; i < NUM_BRADYS; i++)
      @{
         if (nc_inq_enum_member(ncid, typeid, i, name_in, &value_in)) ERR;
         if (strcmp(name_in, brady_name[i]) || value_in != brady_value[i]) ERR;
         if (nc_inq_enum_ident(ncid, typeid, brady_value[i], name_in)) ERR;
         if (strcmp(name_in, brady_name[i])) ERR;
      @}

@end example

@node nc_inq_enum_member, nc_inq_enum_ident, nc_inq_enum, User Defined Data Types
@section Learn the Name of a Enum Type: nc_inq_enum_member
@findex nc_inq_enum_member

Get information about a member of an enum type.

@heading Usage 

@example
int nc_inq_enum_member(int ncid, nc_type xtype, int idx, char *name, 
                       void *value);
@end example

@table @code

@item ncid
The groupid where this enum type exists.

@item xtype
The typeid for this enum type.

@item idx
The zero-based index number for the member of interest. 

@item name
If non-NULL, a pointer to an already allocated char array which will
get the name, as a null terminated string. It will have a maximum
length of NC_MAX_NAME+1.

@item value
If non-NULL, a pointer to storage of the correct integer type
(i.e. the base type of this enum type). It will get the value
associated with this member.

@end table

@heading Errors

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad type id. 

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@end table

@heading Example

This is the continuation of the example in @ref{nc_def_enum}. The file
is reopened and the cloud enum type is examined.

@example
       /* Reopen the file. */
       if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;

       if (nc_inq_user_type(ncid, typeid, name_in, &base_size_in, &base_nc_type_in,
                            &nfields_in, &class_in)) ERR;
       if (strcmp(name_in, TYPE2_NAME) || 
           base_size_in != sizeof(unsigned char) ||
           base_nc_type_in != NC_UBYTE || 
           nfields_in != num_members || 
           class_in != NC_ENUM) ERR;
       if (nc_inq_enum(ncid, typeid, name_in, 
                       &base_nc_type_in, &base_size_in, &num_members_in)) ERR;
       if (strcmp(name_in, TYPE2_NAME) || 
           base_nc_type_in !=  NC_UBYTE || 
           num_members_in != num_members) ERR;
       for (i = 0; i < num_members; i++)
       @{
           if (nc_inq_enum_member(ncid, typeid, i, name_in, &value_in)) ERR;
           if (strcmp(name_in, cloud_types[i].name) || 
               value_in != cloud_types[i].value) ERR;
           if (nc_inq_enum_ident(ncid, typeid, cloud_types[i].value, 
                                 name_in)) ERR;
           if (strcmp(name_in, cloud_types[i].name)) ERR;
       @}
       if (nc_inq_varid(ncid, VAR2_NAME, &varid)) ERR;

       if (nc_get_att(ncid, varid, ATT2_NAME, &value_in)) ERR;
       if (value_in != MISSING) ERR;

       if(nc_get_var(ncid, varid, cloud_data_in)) ERR;
       for (i = 0; i < DIM2_LEN; i++) @{
           if (cloud_data_in[i] != cloud_data[i]) ERR;
       @}
   
       if (nc_close(ncid)) ERR; 
@end example


@node nc_inq_enum_ident,  , nc_inq_enum_member, User Defined Data Types
@section Learn the Name of a Enum Type: nc_inq_enum_ident
@findex nc_inq_enum_ident

Get the name which is associated with an enum member value.

@heading Usage 

@example
int nc_inq_enum_ident(int ncid, nc_type xtype, long long value, char *identifier);
@end example

@table @code

@item ncid
The groupid where this enum type exists.

@item xtype
The typeid for this enum type.

@item value
The value for which an identifier is sought.

@item identifier
If non-NULL, a pointer to an already allocated char array which will
get the identifier, as a null terminated string. It will have a
maximum length of NC_MAX_NAME+1.

@end table

@heading Return Code

@table @code

@item NC_NOERR
No error.

@item NC_EBADTYPEID
Bad type id, or not an enum type.

@item NC_EHDFERR
An error was reported by the HDF5 layer.

@item NC_EINVAL
The value was not found in the enum.

@end table

@heading Example

See the example section for @ref{nc_inq_enum} for a full example.

@node Variables, Attributes, User Defined Data Types, Top
@chapter Variables

@menu
* Variable Introduction::       
* Variable Types::              
* NetCDF-3 Variable Types::     
* NetCDF-4 Atomic Types::       
* nc_def_var::                  Create a Variable
* nc_def_var_chunking::         Set chunking parameters
* nc_inq_var_chunking::         Learn about chunking parameters
* nc_set_var_chunk_cache::      
* nc_get_var_chunk_cache::      
* nc_def_var_fill::             
* nc_inq_var_fill::             
* nc_def_var_deflate::          Set compression parameters
* nc_inq_var_deflate::          Learn about compression parameters
* nc_inq_var_szip::             
* nc_def_var_fletcher32::       Set checksum filter
* nc_inq_var_fletcher32::       Learn if checksum filter is set
* nc_def_var_endian::           
* nc_inq_var_endian::           
* nc_inq_varid::                Get a Variable ID from Its Name
* nc_inq_var::                  Get Information about a Variable from Its ID
* nc_put_var1_ type::           Write a Single Data Value
* nc_put_var_ type::            Write an Entire Variable
* nc_put_vara_ type::           Write an Array of Values
* nc_put_vars_ type::           Write a Subsampled Array of Values
* nc_put_varm_ type::           Write a Mapped Array of Values
* nc_get_var1_ type::           Read a Single Data Value
* nc_get_var_ type::            Read an Entire Variable
* nc_get_vara_ type::           Read an Array of Values
* nc_get_vars_ type::           Read a Subsampled Array of Values
* nc_get_varm_ type::           Read a Mapped Array of Values
* Strings::                     Reading and Writing Character String Values
* nc_free_string::              
* Fill Values::                 What's Written Where there's No Data?
* nc_rename_var::               Rename a Variable
* nc_copy_var::                 
* nc_var_par_access::           
* nc_var_ubyte::                Deprecated variable ``_ubyte'' functions
@end menu

@node Variable Introduction, Variable Types, Variables, Variables
@section Introduction
@cindex appending data to variable

Variables for a netCDF dataset are defined when the dataset is
created, while the netCDF dataset is in define mode. Other variables
may be added later by reentering define mode. A netCDF variable has a
name, a type, and a shape, which are specified when it is defined. A
variable may also have values, which are established later in data
mode.

Ordinarily, the name, type, and shape are fixed when the variable is
first defined. The name may be changed, but the type and shape of a
variable cannot be changed. However, a variable defined in terms of
the unlimited dimension can grow without bound in that dimension.

A netCDF variable in an open netCDF dataset is referred to by a small
integer called a variable ID.

Variable IDs reflect the order in which variables were defined within
a netCDF dataset. Variable IDs are 0, 1, 2,..., in the order in which
the variables were defined. A function is available for getting the
variable ID from the variable name and vice-versa.

Attributes (@pxref{Attributes}) may be associated with a variable to
specify such properties as units.

Operations supported on variables are:
@itemize

@item
Create a variable, given its name, data type, and shape. 

@item
Get a variable ID from its name. 

@item
Get a variable's name, data type, shape, and number of attributes from
its ID.

@item
Put a data value into a variable, given variable ID, indices, and
value.

@item
Put an array of values into a variable, given variable ID, corner
indices, edge lengths, and a block of values.

@item
Put a subsampled or mapped array-section of values into a variable,
given variable ID, corner indices, edge lengths, stride vector, index
mapping vector, and a block of values.

@item
Get a data value from a variable, given variable ID and indices. 

@item
Get an array of values from a variable, given variable ID, corner
indices, and edge lengths.

@item
Get a subsampled or mapped array-section of values from a variable,
given variable ID, corner indices, edge lengths, stride vector, and
index mapping vector.

@item
Rename a variable. 
@end itemize

@node Variable Types, NetCDF-3 Variable Types, Variable Introduction, Variables
@section Language Types Corresponding to netCDF external data types
@cindex bit lengths of data types

NetCDF supported six atomic data types through version 3.6.0 (char,
byte, short, int, float, and double). Starting with version 4.0, many
new atomic and user defined data types are supported (unsigned int
types, strings, compound types, variable length arrays, enums,
opaque). 

The additional data types are only supported in netCDF-4/HDF5
files. To create netCDF-4/HDF5 files, use the HDF5 flag in
nc_create. (@pxref{nc_create}).

@node NetCDF-3 Variable Types, NetCDF-4 Atomic Types, Variable Types, Variables
@section NetCDF-3 Classic and 64-Bit Offset Data Types
@cindex bit lengths of netcdf-3 data types

NetCDF-3 classic and 64-bit offset files support 6 atomic data types,
and none of the user defined datatype introduced in NetCDF-4.

The following table gives the netCDF-3 external data types and the
corresponding type constants for defining variables in the C
interface:

@multitable @columnfractions .25 .60 .15
@item Type @tab C #define @tab Bits

@item byte
@tab NC_BYTE 
@tab 8
 
@item char
@tab NC_CHAR 
@tab 8
 
@item short
@tab NC_SHORT 
@tab 16
 
@item int
@tab NC_INT 
@tab 32
 
@item float
@tab NC_FLOAT 
@tab 32
 
@item double
@tab NC_DOUBLE 
@tab 64
@end multitable
 
The first column gives the netCDF external data type, which is the
same as the CDL data type. The next column gives the corresponding C
pre-processor macro for use in netCDF functions (the pre-processor
macros are defined in the netCDF C header-file netcdf.h). The last
column gives the number of bits used in the external representation of
values of the corresponding type.

@node NetCDF-4 Atomic Types, nc_def_var, NetCDF-3 Variable Types, Variables
@section NetCDF-4 Atomic Types
@cindex bit lengths of netcdf-4 data types

NetCDF-4 files support all of the atomic data types from netCDF-3,
plus additional unsigned integer types, 64-bit integer types, and a
string type.

@multitable @columnfractions .25 .60 .15
@item Type @tab C #define @tab Bits

@item byte
@tab NC_BYTE
@tab 8
 
@item unsigned byte
@tab NC_UBYTE^
@tab 8
 
@item char
@tab NC_CHAR 
@tab 8
 
@item short
@tab NC_SHORT 
@tab 16
 
@item unsigned short
@tab NC_USHORT^
@tab 16
 
@item int
@tab NC_INT 
@tab 32
 
@item unsigned int
@tab NC_UINT^
@tab 32
 
@item unsigned long long
@tab NC_UINT64^
@tab 64
 
@item long long
@tab NC_INT64^
@tab 64
 
@item float
@tab NC_FLOAT 
@tab 32
 
@item double
@tab NC_DOUBLE 
@tab 64

@item char **
@tab NC_STRING^
@tab string length + 1
 
@end multitable

^This type was introduced in netCDF-4, and is not supported in netCDF
classic or 64-bit offset format files, or in netCDF-4 files if they
are created with the NC_CLASSIC_MODEL flags.
 
@node nc_def_var, nc_def_var_chunking, NetCDF-4 Atomic Types, Variables
@section Create a Variable: @code{nc_def_var}
@findex nc_def_var
@cindex nc_def_var, example
@cindex creating variables
@cindex variables, creating

The function nc_def_var adds a new variable to an open netCDF dataset
in define mode. It returns (as an argument) a variable ID, given the
netCDF ID, the variable name, the variable type, the number of
dimensions, and a list of the dimension IDs.

@heading Usage 

@example
int nc_def_var (int ncid, const char *name, nc_type xtype,
                int ndims, const int dimids[], int *varidp);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item name
Variable name.
 
@item xtype
One of the set of predefined netCDF external data types. The type of
this parameter, nc_type, is defined in the netCDF header file. The
valid netCDF external data types are NC_BYTE, NC_CHAR, NC_SHORT,
NC_INT, NC_FLOAT, and NC_DOUBLE. If the file is a NetCDF-4/HDF5 file,
the additional types NC_UBYTE, NC_USHORT, NC_UINT, NC_INT64,
NC_UINT64, and NC_STRING may be used, as well as a user defined type
ID.
 
@item ndims
Number of dimensions for the variable. For example, 2 specifies a
matrix, 1 specifies a vector, and 0 means the variable is a scalar
with no dimensions. Must not be negative or greater than the
predefined constant NC_MAX_VAR_DIMS.
 
@item dimids
Vector of ndims dimension IDs corresponding to the variable
dimensions. For classic model netCDF files, if the ID of the unlimited
dimension is included, it must be first. This argument is ignored if
ndims is 0. For expanded model netCDF4/HDF5 files, there may be any
number of unlimited dimensions, and they may be used in any element of
the dimids array.
 
@item varidp
Pointer to location for the returned variable ID.

@end table

@heading Errors 

nc_def_var returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@table @code

@item NC_NOERR
No error.

@item NC_BADID
Bad ncid.

@item NC_ENOTINDEFINE
Not in define mode. This is returned for netCDF classic or 64-bit
offset files, or for netCDF-4 files, when they were been created with
NC_STRICT_NC3 flag. (@pxref{nc_create}).

@item NC_ESTRICTNC3
Trying to create a var some place other than the root group in a
netCDF file with NC_STRICT_NC3 turned on.

@item NC_MAX_VARS
Max number of variables exceeded in a classic or 64-bit offset file,
or an netCDF-4 file with NC_STRICT_NC3 on.

@item NC_EBADTYPE
Bad type.

@item NC_EINVAL
Number of dimensions to large.

@item NC_ENAMEINUSE
Name already in use. 

@item NC_EPERM
Attempt to create object in read-only file.

@end table

@heading Example

Here is an example using nc_def_var to create a variable named rh of
type double with three dimensions, time, lat, and lon in a new netCDF
dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int  status;                       /* error status */
int  ncid;                         /* netCDF ID */
int  lat_dim, lon_dim, time_dim;   /* dimension IDs */
int  rh_id;                        /* variable ID */
int  rh_dimids[3];                 /* variable shape */
   ... 
status = nc_create("foo.nc", NC_NOCLOBBER, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
                                   /* define dimensions */
status = nc_def_dim(ncid, "lat", 5L, &lat_dim);
if (status != NC_NOERR) handle_error(status);
status = nc_def_dim(ncid, "lon", 10L, &lon_dim);
if (status != NC_NOERR) handle_error(status);
status = nc_def_dim(ncid, "time", NC_UNLIMITED, &time_dim);
if (status != NC_NOERR) handle_error(status);
   ... 
                                   /* define variable */
rh_dimids[0] = time_dim;
rh_dimids[1] = lat_dim;
rh_dimids[2] = lon_dim;
status = nc_def_var (ncid, "rh", NC_DOUBLE, 3, rh_dimids, &rh_id);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_def_var_chunking, nc_inq_var_chunking, nc_def_var, Variables
@section Define Chunking Parameters for a Variable: @code{nc_def_var_chunking}
@findex nc_def_var_chunking
@cindex chunking
@cindex contiguous
@cindex variables, chunking
@cindex variables, contiguous

The function nc_def_var_chunking sets the chunking parameters for a
variable in a netCDF-4 file.  It can set the chunk sizes to get chunked
storage, or it can set the contiguous flag to get contiguous storage.

Variables that make use of one or more unlimited dimensions,
compression, or checksums must use chunking.  Such variables are
created with default chunk sizes of 1 for each unlimited dimension and
the dimension length for other dimensions, except that if the
resulting chunks are too large, the default chunk sizes for non-record
dimensions are reduced.

The total size of a chunk must be less than 4 GiB. That is, the product
of all chunksizes and the size of the data (or the size of nc_vlen_t
for VLEN types) must be less than 4 GiB.

This function may only be called after the variable is defined, but
before nc_enddef is called.  Once the chunking parameters are set for
a variable, they cannot be changed.  This function can be used to
change the default chunking for record, compressed, or checksummed
variables before nc_enddef is called.

Note that you cannot set chunking for scalar variables. Only non-scalar
variables can have chunking.

@heading Usage 

@example
int nc_def_var_chunking(int ncid, int varid, int storage, size_t *chunksizesp);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item storage
If NC_CONTIGUOUS, then contiguous storage is used for this
variable. Variables with chunking, compression, checksums, or one or
more unlimited dimensions cannot use contiguous storage.

If NC_CHUNKED, then chunked storage is used for this variable.
Chunk sizes may be specified with the chunksizes parameter or
default sizes will be used if that parameter is NULL.

By default contiguous storage is used for fix-sized variables when
conpression, chunking, and checksums are not used.

@item *chunksizes
A pointer to an array list of chunk sizes. The array must have one
chunksize for each dimension of the variable.

@end table

@heading Errors 

nc_def_var_chunking returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. 

Possible return codes include:

@table @code

@item NC_NOERR
No error.

@item NC_EBADID
Bad ncid.

@item NC_EINVAL
Invalid input. This can occur if contiguous storage is set on a
variable which uses compression, checksums, or one or more unlimited
dimensions.

@item NC_ENOTNC4
Not a netCDF-4 file.

@item NC_ENOTVAR
Can't find this variable.

@item NC_ELATEDEF
This variable has already been the subject of a nc_enddef call. In
netCDF-4 files nc_enddef will be called automatically for any data
read or write. Once nc_enddef has been called after the nc_def_var call
for a variable, it is impossible to set the chunking for that variable.

@item NC_ENOTINDEFINE
Not in define mode. This is returned for netCDF classic or 64-bit
offset files, or for netCDF-4 files, when they were been created with
NC_STRICT_NC3 flag. (@pxref{nc_create}).

@item NC_ESTRICTNC3
Trying to create a var some place other than the root group in a
netCDF file with NC_STRICT_NC3 turned on.

@item NC_EPERM
Attempt to create object in read-only file.

@end table

@heading Example

In this example from libsrc4/tst_vars2.c, chunksizes are set with
nc_var_def_chunking, and checked with nc_var_inq_chunking.

@example
   printf("**** testing chunking...");
   @{
#define NDIMS5 1
#define DIM5_NAME "D5"
#define VAR_NAME5 "V5"
#define DIM5_LEN 1000

      int dimids[NDIMS5], dimids_in[NDIMS5];
      int varid;
      int ndims, nvars, natts, unlimdimid;
      nc_type xtype_in;
      char name_in[NC_MAX_NAME + 1];
      int data[DIM5_LEN], data_in[DIM5_LEN];
      size_t chunksize[NDIMS5] = @{5@};
      size_t chunksize_in[NDIMS5];
      int storage_in;
      int i, d;

      for (i = 0; i < DIM5_LEN; i++)
         data[i] = i;

      /* Create a netcdf-4 file with one dim and one var. */
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
      if (nc_def_dim(ncid, DIM5_NAME, DIM5_LEN, &dimids[0])) ERR;
      if (nc_def_var(ncid, VAR_NAME5, NC_INT, NDIMS5, dimids, &varid)) ERR;
      if (nc_def_var_chunking(ncid, varid, NC_CHUNKED, chunksize)) ERR;
      if (nc_put_var_int(ncid, varid, data)) ERR;

      /* Check stuff. */
      if (nc_inq_var_chunking(ncid, varid, &storage_in, chunksize_in)) ERR;
      for (d = 0; d < NDIMS5; d++)
         if (chunksize[d] != chunksize_in[d]) ERR;
      if (storage_in != NC_CHUNKED) ERR;
@end example

@node nc_inq_var_chunking, nc_set_var_chunk_cache, nc_def_var_chunking, Variables
@section Learn About Chunking Parameters for a Variable: @code{nc_inq_var_chunking}
@findex nc_inq_var_chunking

The function nc_inq_var_chunking returns the chunking settings for a
variable in a netCDF-4 file. 

@heading Usage 

@example
int nc_inq_var_chunking(int ncid, int varid, int *storagep, size_t *chunksizesp);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item storagep
Address of returned storage property, returned as NC_CONTIGUOUS if this
variable uses contiguous storage, or NC_CHUNKEDif it uses chunked
storage.

@item *chunksizesp
A pointer to an array list of chunk sizes. The array must have
one chunksize for each dimension in the variable.

@end table

@heading Errors 

nc_inq_var_chunking returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. 

Possible return codes include:

@table @code

@item NC_NOERR
No error.

@item NC_BADID
Bad ncid.

@item NC_ENOTNC4
Not a netCDF-4 file.

@item NC_ENOTVAR
Can't find this variable.

@end table

@heading Example

This example is from libsrc4/tst_vars2.c in which a variable with
contiguous storage is created, and then checked with nc_inq_var_chunking:

@example
   printf("**** testing contiguous storage...");
   @{
#define NDIMS6 1
#define DIM6_NAME "D5"
#define VAR_NAME6 "V5"
#define DIM6_LEN 100

      int dimids[NDIMS6], dimids_in[NDIMS6];
      int varid;
      int ndims, nvars, natts, unlimdimid;
      nc_type xtype_in;
      char name_in[NC_MAX_NAME + 1];
      int data[DIM6_LEN], data_in[DIM6_LEN];
      size_t chunksize_in[NDIMS6];
      int storage_in;
      int i, d;

      for (i = 0; i < DIM6_LEN; i++)
         data[i] = i;

      /* Create a netcdf-4 file with one dim and one var. */
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
      if (nc_def_dim(ncid, DIM6_NAME, DIM6_LEN, &dimids[0])) ERR;
      if (dimids[0] != 0) ERR;
      if (nc_def_var(ncid, VAR_NAME6, NC_INT, NDIMS6, dimids, &varid)) ERR;
      if (nc_def_var_chunking(ncid, varid, NC_CONTIGUOUS, NULL)) ERR;
      if (nc_put_var_int(ncid, varid, data)) ERR;

      /* Check stuff. */
      if (nc_inq_var_chunking(ncid, 0, &storage_in, chunksize_in)) ERR;
      if (storage_in != NC_CONTIGUOUS) ERR;
@end example

@node nc_set_var_chunk_cache, nc_get_var_chunk_cache, nc_inq_var_chunking, Variables
@section Set HDF5 Chunk Cache for a Variable: nc_set_var_chunk_cache
@findex nc_set_var_chunk_cache
@cindex HDF5 chunk cache, per-variable

This function changes the chunk cache settings for a variable. The
change in cache size happens immediately. This is a property of the
open file - it does not persist the next time you open the file.

For more information, see the documentation for the H5Pset_cache()
function in the HDF5 library at the HDF5 website:
@uref{@value{hdf5-url}}.

@heading Usage 

@example
nc_set_var_chunk_cache(int ncid, int varid, size_t size, size_t nelems, 
		       float preemption);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item size
The total size of the raw data chunk cache, in bytes. This should be
big enough to hold multiple chunks of data.

@item nelems
The number of chunk slots in the raw data chunk cache hash table. This
should be a prime number larger than the number of chunks that will be
in the cache.

@item preemption
The preemtion value must be between 0 and 1 inclusive and indicates
how much chunks that have been fully read are favored for
preemption. A value of zero means fully read chunks are treated no
differently than other chunks (the preemption is strictly LRU) while a
value of one means fully read chunks are always preempted before other
chunks. 

@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item NC_EINVAL
Preemption must be between zero and one (inclusive). 

@end table

@heading Example 

This example is from libsrc4/tst_vars2.c:

@example
#include <netcdf.h>
   ... 
#define CACHE_SIZE 32000000
#define CACHE_NELEMS 1009
#define CACHE_PREEMPTION .75
   ... 

      /* Create a netcdf-4 file with one dim and one var. */
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
      if (nc_def_dim(ncid, DIM5_NAME, DIM5_LEN, &dimids[0])) ERR;
      if (dimids[0] != 0) ERR;
      if (nc_def_var(ncid, VAR_NAME5, NC_INT, NDIMS5, dimids, &varid)) ERR;
      if (nc_def_var_chunking(ncid, varid, NC_CHUNKED, chunksize)) ERR;
      if (nc_set_var_chunk_cache(ncid, varid, CACHE_SIZE, CACHE_NELEMS, CACHE_PREEMPTION)) ERR;

@end example

@node nc_get_var_chunk_cache, nc_def_var_fill, nc_set_var_chunk_cache, Variables
@section Get the HDF5 Chunk Cache Settings for a Variable: nc_get_var_chunk_cache
@findex nc_get_chunk_cache
@cindex HDF5 chunk cache

This function gets the current chunk cache settings for a variable in
a netCDF-4/HDF5 file.

For more information, see the documentation for the H5Pget_cache()
function in the HDF5 library at the HDF5 website:
@uref{@value{hdf5-url}}.

@heading Usage 

@example
int nc_get_var_chunk_cache(int ncid, int varid, size_t *sizep, size_t *nelemsp, 
                           float *preemptionp);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item sizep
The total size of the raw data chunk cache, in bytes, will be put
here. If NULL, will be ignored.

@item nelemsp
The number of chunk slots in the raw data chunk cache hash table will
be put here.  If NULL, will be ignored.


@item preemptionp
The preemption will be put here.  The preemtion value is between 0 and
1 inclusive and indicates how much chunks that have been fully read
are favored for preemption.  A value of zero means fully read chunks
are treated no differently than other chunks (the preemption is
strictly LRU) while a value of one means fully read chunks are always
preempted before other chunks.  If NULL, will be ignored.

@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@end table

@heading Example 

This example is from libsrc4/tst_vars2.c:

@example
#include <netcdf.h>
   ... 
      /* Create a netcdf-4 file with one dim and one var. */
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
      if (nc_def_dim(ncid, DIM5_NAME, DIM5_LEN, &dimids[0])) ERR;
      if (nc_def_var(ncid, VAR_NAME5, NC_INT, NDIMS5, dimids, &varid)) ERR;
      if (nc_def_var_chunking(ncid, varid, NC_CHUNKED, chunksize)) ERR;
      if (nc_set_var_chunk_cache(ncid, varid, CACHE_SIZE, CACHE_NELEMS, 
                                 CACHE_PREEMPTION)) ERR;
   ...
      if (nc_get_var_chunk_cache(ncid, varid, &cache_size_in, &cache_nelems_in, 
				 &cache_preemption_in)) ERR;
      if (cache_size_in != CACHE_SIZE || cache_nelems_in != CACHE_NELEMS ||
	  cache_preemption_in != CACHE_PREEMPTION) ERR;

   ... 
@end example

@node nc_def_var_fill, nc_inq_var_fill, nc_get_var_chunk_cache, Variables
@section Define Fill Parameters for a Variable: @code{nc_def_var_fill}
@findex nc_def_var_fill
@cindex fill
@cindex variables, fill

The function nc_def_var_fill sets the fill parameters for a
variable in a netCDF-4 file. 

This function must be called after the variable is defined, but before
nc_enddef is called.

@heading Usage 

@example
int nc_def_var_fill(int ncid, int varid, int no_fill, void *fill_value);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item no_fill
Set no_fill mode on a variable. When this mode is on, fill values will
not be written for the variable. This is helpful in high performance
applications. For netCDF-4/HDF5 files (whether classic model or not),
this may only be changed after the variable is defined, but before it
is committed to disk (i.e. before the first nc_enddef after the
nc_def_var.) For classic and 64-bit offset file, the no_fill mode may
be turned on and off at any time.

@item *fill_value
A pointer to a value which will be used as the fill value for the
variable. Must be the same type as the variable. This will be written
to a _FillValue attribute, created for this purpose. If NULL, this
argument will be ignored.
 
@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item NC_BADID
Bad ncid.

@item NC_ENOTNC4
Not a netCDF-4 file.

@item NC_ENOTVAR
Can't find this variable.

@item NC_ELATEDEF
This variable has already been the subject of a nc_enddef call. In
netCDF-4 files nc_enddef will be called automatically for any data
read or write. Once enddef has been called, it is impossible to set
the fill for a variable.

@item NC_ENOTINDEFINE
Not in define mode. This is returned for netCDF classic or 64-bit
offset files, or for netCDF-4 files, when they were been created with
NC_STRICT_NC3 flag. (@pxref{nc_create}).

@item NC_EPERM
Attempt to create object in read-only file.

@end table

@heading Example

This example is from libsrc4/tst_vars.c

@example
      int dimids[NDIMS];
      size_t index[NDIMS];
      int varid;
      int no_fill;
      unsigned short ushort_data = 42, ushort_data_in, fill_value_in;

      /* Create a netcdf-4 file with one dim and 1 NC_USHORT var. */
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
      if (nc_def_dim(ncid, DIM7_NAME, DIM7_LEN, &dimids[0])) ERR;
      if (nc_def_var(ncid, VAR7_NAME, NC_USHORT, NDIMS, dimids,
		     &varid)) ERR;
      if (nc_def_var_fill(ncid, varid, 1, NULL)) ERR;
@end example

@node nc_inq_var_fill, nc_def_var_deflate, nc_def_var_fill, Variables
@section Learn About Fill Parameters for a Variable: @code{nc_inq_var_fill}
@findex nc_inq_var_fill

The function nc_inq_var_fill returns the fill settings for a
variable in a netCDF-4 file. 

@heading Usage 

@example
int nc_inq_var_fill(int ncid, int varid, int *no_fill, void *fill_value);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item *no_fill
Pointer to an integer which will get a 1 if no_fill mode is set for
this variable. @xref{nc_def_var_fill}. This parameter will be ignored
if it is NULL.

@item *fill_value
A pointer which will get the fill value for this variable. This
parameter will be ignored if it is NULL.

@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item NC_BADID
Bad ncid.

@item NC_ENOTNC4
Not a netCDF-4 file.

@item NC_ENOTVAR
Can't find this variable.

@end table

@heading Example

This example is from libsrc4/tst_vars.c

@example
      int dimids[NDIMS];
      size_t index[NDIMS];
      int varid;
      int no_fill;
      unsigned short ushort_data = 42, ushort_data_in, fill_value_in;

      /* Create a netcdf-4 file with one dim and 1 NC_USHORT var. */
      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
      if (nc_def_dim(ncid, DIM7_NAME, DIM7_LEN, &dimids[0])) ERR;
      if (nc_def_var(ncid, VAR7_NAME, NC_USHORT, NDIMS, dimids,
		     &varid)) ERR;
      if (nc_def_var_fill(ncid, varid, 1, NULL)) ERR;

      /* Check stuff. */
      if (nc_inq_var_fill(ncid, varid, &no_fill, &fill_value_in)) ERR;
      if (!no_fill) ERR;
@end example

@node nc_def_var_deflate, nc_inq_var_deflate, nc_inq_var_fill, Variables
@section Define Compression Parameters for a Variable: @code{nc_def_var_deflate}
@findex nc_def_var_deflate
@cindex deflate
@cindex variables, setting deflate
@cindex compression, setting parameters

The function nc_def_var_deflate sets the deflate parameters for a
variable in a netCDF-4 file. 

This function must be called after the variable is defined, but before
nc_enddef is called.

This does not work with scalar variables.

@heading Usage 

@example
nc_def_var_deflate(int ncid, int varid, int shuffle, int deflate, 
                   int deflate_level);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item shuffle
If non-zero, turn on the shuffle filter.

@item deflate
If non-zero, turn on the deflate filter at the level specified by the
deflate_level parameter.

@item deflate_level
If the deflate parameter is non-zero, set the deflate level to this
value. Must be between 0 and 9.
 
@end table

@heading Errors 

nc_def_var_deflate returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. 

Possible return codes include:

@table @code

@item NC_NOERR
No error.

@item NC_BADID
Bad ncid.

@item NC_ENOTNC4
Not a netCDF-4 file.

@item NC_ENOTVAR
Can't find this variable.

@item NC_ELATEDEF
This variable has already been the subject of a nc_enddef call. In
netCDF-4 files nc_enddef will be called automatically for any data
read or write. Once enddef has been called, it is impossible to set
the deflate for a variable.

@item NC_ENOTINDEFINE
Not in define mode. This is returned for netCDF classic or 64-bit
offset files, or for netCDF-4 files, when they were been created with
NC_STRICT_NC3 flag. (@pxref{nc_create}).

@item NC_EPERM
Attempt to create object in read-only file.

@item NC_EINVAL
Invalid deflate_level. The deflate level must be between 0 and 9,
inclusive.

@end table

@heading Example

@example
@end example

@node nc_inq_var_deflate, nc_inq_var_szip, nc_def_var_deflate, Variables
@section Learn About Deflate Parameters for a Variable: @code{nc_inq_var_deflate}
@findex nc_inq_var_deflate

The function nc_inq_var_deflate returns the deflate settings for a
variable in a netCDF-4 file. 

@heading Usage 

@example
nc_inq_var_deflate(int ncid, int varid, int *shufflep, 
                   int *deflatep, int *deflate_levelp);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item *shufflep
If this pointer is non-NULL, the nc_inq_var_deflate function will
write a 1 if the shuffle filter is turned on for this variable, and a
0 otherwise.

@item *deflatep
If this pointer is non-NULL, the nc_inq_var_deflate function will
write a 1 if the deflate filter is turned on for this variable, and a
0 otherwise.

@item *deflate_levelp
If this pointer is non-NULL, and the deflate filter is in use for this
variable, the nc_inq_var_deflate function will write the deflate_level
here.
 
@end table

@heading Errors 

nc_inq_var_deflate returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. 

Possible return codes include:

@table @code

@item NC_NOERR
No error.

@item NC_BADID
Bad ncid.

@item NC_ENOTNC4
Not a netCDF-4 file.

@item NC_ENOTVAR
Can't find this variable.

@end table

@heading Example

@example
@end example

@node nc_inq_var_szip, nc_def_var_fletcher32, nc_inq_var_deflate, Variables
@section Learn About Szip Parameters for a Variable: @code{nc_inq_var_szip}
@findex nc_inq_var_szip

The function nc_inq_var_szip returns the szip settings for a
variable in a netCDF-4 file. 

@heading Usage 

@example
int nc_inq_var_szip(int ncid, int varid, int *options_maskp, int *pixels_per_blockp);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item *options_maskp
If this pointer is non-NULL, the nc_inq_var_szip function will
put the options_mask here.

@item *pixels_per_blockp
If this pointer is non-NULL, the nc_inq_var_szip function will
write the bits per pixel here.

@end table

@heading Errors 

nc_inq_var_szip returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error.

Possible return codes include:

@table @code

@item NC_NOERR
No error.

@item NC_BADID
Bad ncid.

@item NC_ENOTNC4
Not a netCDF-4 file.

@item NC_ENOTVAR
Can't find this variable.

@end table

@heading Example
This example is from libsrc4/tst_vars3.c.

@example
      /* Make sure we have the szip settings we expect. */
      if (nc_inq_var_szip(ncid, small_varid, &options_mask_in, &pixels_per_block_in)) ERR;
      if (options_mask_in != 0 || pixels_per_block_in !=0) ERR;
      if (nc_inq_var_szip(ncid, medium_varid, &options_mask_in, &pixels_per_block_in)) ERR;
      if (!(options_mask_in & NC_SZIP_EC_OPTION_MASK) || pixels_per_block_in != 32) ERR;
      if (nc_inq_var_szip(ncid, large_varid, &options_mask_in, &pixels_per_block_in)) ERR;
      if (!(options_mask_in & NC_SZIP_NN_OPTION_MASK) || pixels_per_block_in != 16) ERR;
@end example

@node nc_def_var_fletcher32, nc_inq_var_fletcher32, nc_inq_var_szip, Variables
@section Define Checksum Parameters for a Variable: @code{nc_def_var_fletcher32}
@findex nc_def_var_fletcher32
@cindex checksum
@cindex fletcher32
@cindex variables, fletcher32
@cindex variables, checksum

The function nc_def_var_fletcher32 sets the checksum parameters for a
variable in a netCDF-4 file. 

This function may only be called after the variable is defined, but before
nc_enddef is called.

@heading Usage 

@example
nc_def_var_fletcher32(int ncid, int varid, int checksum);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item checksum
If this is NC_FLETCHER32, fletcher32 checksums will be turned on for this
variable.
 
@end table

@heading Errors 

nc_def_var_fletcher32 returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. 

Possible return codes include:

@table @code

@item NC_NOERR
No error.

@item NC_BADID
Bad ncid.

@item NC_ENOTNC4
Not a netCDF-4 file.

@item NC_ENOTVAR
Can't find this variable.

@item NC_ELATEDEF
This variable has already been the subject of a nc_enddef call. In
netCDF-4 files nc_enddef will be called automatically for any data
read or write. Once enddef has been called, it is impossible to set
the checksum property for a variable.

@item NC_ENOTINDEFINE
Not in define mode. This is returned for netCDF classic or 64-bit
offset files, or for netCDF-4 files, when they were been created with
NC_STRICT_NC3 flag. (@pxref{nc_create}).

@item NC_EPERM
Attempt to create object in read-only file.

@end table

@heading Example

@example
@end example

@node nc_inq_var_fletcher32, nc_def_var_endian, nc_def_var_fletcher32, Variables
@section Learn About Checksum Parameters for a Variable: @code{nc_inq_var_fletcher32}
@findex nc_inq_var_fletcher32

The function nc_inq_var_fletcher32 returns the checksum settings for a
variable in a netCDF-4 file. 

@heading Usage 

@example
nc_inq_var_fletcher32(int ncid, int varid, int *checksump);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item *checksump
If not-NULL, the nc_inq_var_fletcher32 function will set the int pointed
at to NC_FLETCHER32 if the fletcher32 checksum filter is turned on for
this variable, and NC_NOCHECKSUM if it is not.

@end table

@heading Errors 

nc_inq_var_fletcher32 returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. 

Possible return codes include:

@table @code

@item NC_NOERR
No error.

@item NC_BADID
Bad ncid.

@item NC_ENOTNC4
Not a netCDF-4 file.

@item NC_ENOTVAR
Can't find this variable.

@end table

@heading Example

@example
@end example

@node nc_def_var_endian, nc_inq_var_endian, nc_inq_var_fletcher32, Variables
@section Define Endianness of a Variable: @code{nc_def_var_endian}
@findex nc_def_var_endian
@cindex endianness
@cindex big-endian
@cindex little-endian
@cindex variables, endian

The function nc_def_var_endian sets the endianness for a variable in a
netCDF-4 file.

This function must be called after the variable is defined, but before
nc_enddef is called.

By default, netCDF-4 variables are in native endianness. That is, they
are big-endian on a big-endian machine, and little-endian on a little
endian machine.

In some cases a user might wish to change from native endianness to
either big or little-endianness. This function allows them to do that.

@heading Usage 

@example
nc_def_var_endian(int ncid, int varid, int endian);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item endian
Set to NC_ENDIAN_NATIVE for native endianness. (This is the
default). Set to NC_ENDIAN_LITTLE for little endian, or NC_ENDIAN_BIG
for big endian.
 
@end table

@heading Errors 

nc_def_var_endian returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. 

Possible return codes include:

@table @code

@item NC_NOERR
No error.

@item NC_BADID
Bad ncid.

@item NC_ENOTNC4
Not a netCDF-4 file.

@item NC_ENOTVAR
Can't find this variable.

@item NC_ELATEDEF
This variable has already been the subject of a nc_enddef call. In
netCDF-4 files nc_enddef will be called automatically for any data
read or write. Once enddef has been called, it is impossible to set
the endianness of a variable.

@item NC_ENOTINDEFINE
Not in define mode. This is returned for netCDF classic or 64-bit
offset files, or for netCDF-4 files, when they were been created with
NC_STRICT_NC3 flag, and the file is not in define mode. (@pxref{nc_create}).

@item NC_EPERM
Attempt to create object in read-only file.

@end table

@heading Example

@example
@end example

@node nc_inq_var_endian, nc_inq_varid, nc_def_var_endian, Variables
@section Learn About Endian Parameters for a Variable: @code{nc_inq_var_endian}
@findex nc_inq_var_endian

The function nc_inq_var_endian returns the endianness settings for a
variable in a netCDF-4 file.

@heading Usage 

@example
nc_inq_var_endian(int ncid, int varid, int *endianp);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.

@item *endianp
If not-NULL, the nc_inq_var_endian function will set the int
pointed to this to NC_ENDIAN_LITTLE if this variable is stored in
little-endian format, NC_ENDIAN_BIG if it is stored in big-endian
format, and NC_ENDIAN_NATIVE if the endianness is not set, and the
variable is not created yet.

@end table

@heading Errors 

nc_inq_var_endian returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. 

Possible return codes include:

@table @code

@item NC_NOERR
No error.

@item NC_BADID
Bad ncid.

@item NC_ENOTNC4
Not a netCDF-4 file.

@item NC_ENOTVAR
Can't find this variable.

@end table

@heading Example

@example
@end example

@node nc_inq_varid, nc_inq_var, nc_inq_var_endian, Variables
@section Get a Variable ID from Its Name: nc_inq_varid 
@findex nc_inq_varid
@cindex nc_inq_varid, example
@cindex variables, inquiring about
@cindex inquiring about variables

The function nc_inq_varid returns the ID of a netCDF variable, given
its name.

@heading Usage
@example
int nc_inq_varid (int ncid, const char *name, int *varidp);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item name
Variable name for which ID is desired.
 
@item varidp
Pointer to location for returned variable ID.
@end table

@heading Errors 

nc_inq_varid returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The specified variable name is not a valid name for a variable in the
specified netCDF dataset.

@item
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Example

Here is an example using nc_inq_varid to find out the ID of a variable
named rh in an existing netCDF dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int  status, ncid, rh_id;
   ... 
status = nc_open("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_inq_var, nc_put_var1_ type, nc_inq_varid, Variables
@section Get Information about a Variable from Its ID: nc_inq_var
family
@findex nc_inq_var
&findex nc_inq_vardimid
@findex nc_inq_varname
@findex nc_inq_vartype
@findex nc_inq_varndims
@findex nc_inq_varnatts
@cindex nc_inq_var, example
@cindex variables, getting name

A family of functions that returns information about a netCDF
variable, given its ID. Information about a variable includes its
name, type, number of dimensions, a list of dimension IDs describing
the shape of the variable, and the number of variable attributes that
have been assigned to the variable.

The function nc_inq_var returns all the information about a netCDF
variable, given its ID. The other functions each return just one item
of information about a variable.

These other functions include nc_inq_varname, nc_inq_vartype,
nc_inq_varndims, nc_inq_vardimid, and nc_inq_varnatts.

@heading Usage 
@example
int nc_inq_var      (int ncid, int varid, char *name, nc_type *xtypep,
                     int *ndimsp, int dimids[], int *nattsp);
int nc_inq_varname  (int ncid, int varid, char *name);
int nc_inq_vartype  (int ncid, int varid, nc_type *xtypep);
int nc_inq_varndims (int ncid, int varid, int *ndimsp);
int nc_inq_vardimid (int ncid, int varid, int dimids[]);
int nc_inq_varnatts (int ncid, int varid, int *nattsp);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.
 
@item name
Returned variable name. The caller must allocate space for the
returned name. The maximum possible length, in characters, of a
variable name is given by the predefined constant NC_MAX_NAME. (This
doesn't include the null terminator, so declare your array to be size
NC_MAX_NAME+1). The returned character array will be null-terminated.
 
@item xtypep
Pointer to location for returned variable type, one of the set of
predefined netCDF external data types. The type of this parameter,
nc_type, is defined in the netCDF header file. The valid netCDF
external data types are NC_BYTE, NC_CHAR, NC_SHORT, NC_INT, NC_FLOAT,
and NC_DOUBLE.
 
@item ndimsp
Pointer to location for returned number of dimensions the variable
was defined as using. For example, 2 indicates a matrix, 1 indicates a
vector, and 0 means the variable is a scalar with no dimensions.
 
@item dimids
Returned vector of *ndimsp dimension IDs corresponding to the
variable dimensions. The caller must allocate enough space for a
vector of at least *ndimsp integers to be returned. The maximum
possible number of dimensions for a variable is given by the
predefined constant NC_MAX_VAR_DIMS.
 
@item nattsp
Pointer to location for returned number of variable attributes
assigned to this variable.
@end table

These functions return the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

The variable ID is invalid for the specified netCDF dataset. 
The specified netCDF ID does not refer to an open netCDF dataset. 

@heading Example

Here is an example using nc_inq_var to find out about a variable named
rh in an existing netCDF dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int  status                        /* error status */
int  ncid;                         /* netCDF ID */
int  rh_id;                        /* variable ID */
nc_type rh_type;                   /* variable type */
int rh_ndims;                      /* number of dims */
int  rh_dimids[NC_MAX_VAR_DIMS];   /* dimension IDs */
int rh_natts                       /* number of attributes */
   ... 
status = nc_open ("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
/* we don't need name, since we already know it */
status = nc_inq_var (ncid, rh_id, 0, &rh_type, &rh_ndims, rh_dimids,
                     &rh_natts);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_put_var1_ type, nc_put_var_ type, nc_inq_var, Variables
@section Write a Single Data Value: nc_put_var1_ @var{type}
@findex nc_put_var1_ type
@cindex nc_put_var1_ type, example
@cindex writing single value
@findex nc_put_var1_text 
@findex nc_put_var1_uchar
@findex nc_put_var1_schar
@findex nc_put_var1_short
@findex nc_put_var1_int  
@findex nc_put_var1_long 
@findex nc_put_var1_float
@findex nc_put_var1_double
@findex nc_put_var1_ushort
@findex nc_put_var1_uint
@findex nc_put_var1_longlong
@findex nc_put_var1_ulonglong
@findex nc_put_var1_string
@findex nc_put_var1

The functions nc_put_var1_ @var{type} put a single data value of the
specified type into a variable of an open netCDF dataset that is in
data mode. Inputs are the netCDF ID, the variable ID, an index that
specifies which value to add or alter, and the data value. The value
is converted to the external data type of the variable, if necessary.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and
string are only available for netCDF-4/HDF5 files.

The nc_put_var1() function will write a variable of any type,
including user defined type. For this function, the type of the data
in memory must match the type of the variable - no data conversion is
done.

@heading Usage 
@example
int nc_put_var1_text  (int ncid, int varid, const size_t index[],
                       const char *tp);
int nc_put_var1_uchar (int ncid, int varid, const size_t index[],
                       const unsigned char *up);
int nc_put_var1_schar (int ncid, int varid, const size_t index[],
                       const signed char *cp);
int nc_put_var1_short (int ncid, int varid, const size_t index[],
                       const short *sp);
int nc_put_var1_int   (int ncid, int varid, const size_t index[],
                       const int *ip);
int nc_put_var1_long  (int ncid, int varid, const size_t index[],
                       const long *lp);
int nc_put_var1_float (int ncid, int varid, const size_t index[],
                       const float *fp); 
int nc_put_var1_double(int ncid, int varid, const size_t index[],
                       const double *dp);
int nc_put_var1_ushort(int ncid, int varid, const size_t index[],
                       const unsigned short *sp);
int nc_put_var1_uint  (int ncid, int varid, const size_t index[],
                       const unsigned int *ip);
int nc_put_var1_longlong(int ncid, int varid, const size_t index[],
                         const long long *ip);
int nc_put_var1_ulonglong(int ncid, int varid, const size_t index[],
                         const unsigned long long *ip);
int nc_put_var1_string(int ncid, int varid, const size_t index[],
                       const char **ip);
int nc_put_var1(int ncid, int varid, const size_t *indexp,
                const void *op);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.
 
@item index[]
The index of the data value to be written. The indices are relative
to 0, so for example, the first data value of a two-dimensional
variable would have index (0,0). The elements of index must correspond
to the variable's dimensions. Hence, if the variable uses the
unlimited dimension, the first index would correspond to the unlimited
dimension.
 
@item tp
@itemx up
@itemx cp
@itemx sp
@itemx ip
@itemx lp
@itemx fp
@itemx dp
Pointer to the data value to be written. If the type of data values
differs from the netCDF variable type, type conversion will
occur. @xref{Type Conversion,,, netcdf, @value{n-man}}.

@end table

@heading Return Codes

@itemize

@item NC_NOERR
No error.

@item NC_EHDFERR
Error reported by HDF5 layer.

@item NC_ENOTVAR
The variable ID is invalid for the specified netCDF dataset.

@item NC_EINVALCOORDS
The specified indices were out of range for the rank of the specified
variable. For example, a negative index or an index that is larger
than the corresponding dimension length will cause an error.

@item NC_ERANGE
The specified value is out of the range of values representable by the
external data type of the variable. (Does not apply to nc_put_var1()
function).

@item NC_EINDEFINE
The specified netCDF is in define mode rather than data mode. 

@item NC_EBADID
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Example

Here is an example using nc_put_var1_double to set the (1,2,3) element
of the variable named rh to 0.5 in an existing netCDF dataset named
foo.nc. For simplicity in this example, we assume that we know that rh
is dimensioned with time, lat, and lon, so we want to set the value of
rh that corresponds to the second time value, the third lat value, and
the fourth lon value:

@example
#include <netcdf.h>
   ... 
int  status;                          /* error status */
int  ncid;                            /* netCDF ID */
int  rh_id;                           /* variable ID */
static size_t rh_index[] = @{1, 2, 3@}; /* where to put value */
static double rh_val = 0.5;           /* value to put */
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_put_var1_double(ncid, rh_id, rh_index, &rh_val);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_put_var_ type, nc_put_vara_ type, nc_put_var1_ type, Variables
@section Write an Entire Variable: nc_put_var_ @var{type} 
@findex nc_put_var_ type
@cindex nc_put_var_ type, example
@cindex writing entire variable
@cindex entire variable, writing
@cindex variable, writing entire
@findex nc_put_var_text  
@findex nc_put_var_uchar 
@findex nc_put_var_schar 
@findex nc_put_var_short 
@findex nc_put_var_int   
@findex nc_put_var_long  
@findex nc_put_var_float 
@findex nc_put_var_double
@findex nc_put_var_ushort
@findex nc_put_var_uint  
@findex nc_put_var_longlong 
@findex nc_put_var_ulonglong
@findex nc_put_var_string
@findex nc_put_var       

The nc_put_var_ @var{type} family of functions write all the values of a
variable into a netCDF variable of an open netCDF dataset. This is the
simplest interface to use for writing a value in a scalar variable or
whenever all the values of a multidimensional variable can all be
written at once. The values to be written are associated with the
netCDF variable by assuming that the last dimension of the netCDF
variable varies fastest in the C interface. The values are converted
to the external data type of the variable, if necessary.

Take care when using the simplest forms of this interface with record
variables (variables that use the NC_UNLIMITED dimension) when you
don't specify how many records are to be written. If you try to write
all the values of a record variable into a netCDF file that has no
record data yet (hence has 0 records), nothing will be
written. Similarly, if you try to write all the values of a record
variable but there are more records in the file than you assume, more
in-memory data will be accessed than you supply, which may result in a
segmentation violation.  To avoid such problems, it is better to use
the nc_put_vara interfaces for variables that use the
NC_UNLIMITED dimension.  @xref{nc_put_vara_ type}.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and
string are only available for netCDF-4/HDF5 files.

The nc_put_var() function will write a variable of any type,
including user defined type. For this function, the type of the data
in memory must match the type of the variable - no data conversion is
done.

@heading Usage 
@example
int nc_put_var_text  (int ncid, int varid, const char *tp);
int nc_put_var_uchar (int ncid, int varid, const unsigned char *up);
int nc_put_var_schar (int ncid, int varid, const signed char *cp);
int nc_put_var_short (int ncid, int varid, const short *sp);
int nc_put_var_int   (int ncid, int varid, const int *ip);
int nc_put_var_long  (int ncid, int varid, const long *lp);
int nc_put_var_float (int ncid, int varid, const float *fp);
int nc_put_var_double(int ncid, int varid, const double *dp);
int nc_put_var_ushort(int ncid, int varid, const unsigned short *op);
int nc_put_var_uint  (int ncid, int varid, const unsigned int *op);
int nc_put_var_longlong (int ncid, int varid, const long long *op);
int nc_put_var_ulonglong(int ncid, int varid, const unsigned long long *op);
int nc_put_var_string(int ncid, int varid, const char **op);
int nc_put_var       (int ncid, int varid,  const void *op);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.
 
@item tp
@itemx up
@itemx cp
@itemx sp
@itemx ip
@itemx lp
@itemx fp
@itemx dp
Pointer to a block of contiguous data values to be written. The order in which
the data will be written to the netCDF variable is with the last
dimension of the specified variable varying fastest. If the type of
data values differs from the netCDF variable type, type conversion
will occur. @xref{Type Conversion,,, netcdf, @value{n-man}}.

@end table

@heading Return Codes

@itemize

@item NC_NOERR
The variable ID is invalid for the specified netCDF dataset. 

@item NC_EHDFERR
Error reported by HDF5 layer.

@item NC_ERANGE
One or more of the specified values are out of the range of values
representable by the external data type of the variable. (Does not
apply to nc_put_var() function).

@item NC_EINDEFINE
The specified netCDF dataset is in define mode rather than data mode.

@item NC_BADID
The specified netCDF ID does not refer to an open netCDF dataset. 

@item NC_ENOTVAR
Bad variable ID.

@end itemize

@heading Example

Here is an example using nc_put_var_double to add or change all the
values of the variable named rh to 0.5 in an existing netCDF dataset
named foo.nc. For simplicity in this example, we assume that we know
that rh is dimensioned with lat and lon, and that there are
five lat values and ten lon values.

@example
#include <netcdf.h>
   ... 
#define LATS  5
#define LONS  10
int  status;                       /* error status */
int  ncid;                         /* netCDF ID */
int  rh_id;                        /* variable ID */
double rh_vals[LATS*LONS];         /* array to hold values */
int i;
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
for (i = 0; i < LATS*LONS; i++)
    rh_vals[i] = 0.5;
/* write values into netCDF variable */
status = nc_put_var_double(ncid, rh_id, rh_vals);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_put_vara_ type, nc_put_vars_ type, nc_put_var_ type, Variables
@section Write an Array of Values: nc_put_vara_ @var{type} 
@findex nc_put_vara_ type
@cindex nc_put_vara_ type, example
@cindex writing array section
@cindex array section, writing
@findex nc_put_vara_ type 
@findex nc_put_vara_text  
@findex nc_put_vara_uchar 
@findex nc_put_vara_schar 
@findex nc_put_vara_short 
@findex nc_put_vara_int   
@findex nc_put_vara_long  
@findex nc_put_vara_float 
@findex nc_put_vara_double
@findex nc_put_vara_ushort
@findex nc_put_vara_uint  
@findex nc_put_vara_longlong 
@findex nc_put_vara_ulonglong
@findex nc_put_vara_string
@findex nc_put_vara       

The function nc_put_vara_ @var{type} writes values into a netCDF variable of
an open netCDF dataset. The part of the netCDF variable to write is
specified by giving a corner and a vector of edge lengths that refer
to an array section of the netCDF variable. The values to be written
are associated with the netCDF variable by assuming that the last
dimension of the netCDF variable varies fastest in the C
interface. The netCDF dataset must be in data mode.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and
string are only available for netCDF-4/HDF5 files.

The nc_put_var() function will write a variable of any type,
including user defined type. For this function, the type of the data
in memory must match the type of the variable - no data conversion is
done.

@heading Usage 
@example
int nc_put_vara_ type (int ncid, int varid, const size_t start[],
                       const size_t count[], const type *valuesp);
int nc_put_vara_text  (int ncid, int varid, const size_t start[],
                       const size_t count[], const char *tp);
int nc_put_vara_uchar (int ncid, int varid, const size_t start[],
                       const size_t count[], const unsigned char *up);
int nc_put_vara_schar (int ncid, int varid, const size_t start[],
                       const size_t count[], const signed char *cp);
int nc_put_vara_short (int ncid, int varid, const size_t start[],
                       const size_t count[], const short *sp);
int nc_put_vara_int   (int ncid, int varid, const size_t start[],
                       const size_t count[], const int *ip);
int nc_put_vara_long  (int ncid, int varid, const size_t start[],
                       const size_t count[], const long *lp);
int nc_put_vara_float (int ncid, int varid, const size_t start[],
                       const size_t count[], const float *fp);
int nc_put_vara_double(int ncid, int varid, const size_t start[],
                       const size_t count[], const double *dp);
int nc_put_vara_ushort(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const unsigned short *op);
int nc_put_vara_uint  (int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const unsigned int *op);
int nc_put_vara_longlong (int ncid, int varid, const size_t *startp, 
                          const size_t *countp, const long long *op);
int nc_put_vara_ulonglong(int ncid, int varid, const size_t *startp, 
                          const size_t *countp, const unsigned long long *op);
int nc_put_vara_string(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const char **op);
int nc_put_vara       (int ncid, int varid,  const size_t *startp, 
                       const size_t *countp, const void *op);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.
 
@item start
A vector of size_t integers specifying the index in the variable
where the first of the data values will be written. The indices are
relative to 0, so for example, the first data value of a variable
would have index (0, 0, ... , 0). The size of start must be the same
as the number of dimensions of the specified variable. The elements of
start must correspond to the variable's dimensions in order. Hence, if
the variable is a record variable, the first index would correspond to
the starting record number for writing the data values.
 
@item count
A vector of size_t integers specifying the edge lengths along each
dimension of the block of data values to be written. To write a single
value, for example, specify count as (1, 1, ... , 1). The length of
count is the number of dimensions of the specified variable. The
elements of count correspond to the variable's dimensions. Hence, if
the variable is a record variable, the first element of count
corresponds to a count of the number of records to write.

Note: setting any element of the count array to zero causes the
function to exit without error, and without doing anything.
 
@item tp
@itemx up
@itemx cp
@itemx sp
@itemx ip
@itemx lp
@itemx fp
@itemx dp
Pointer to a block of contiguous data values to be written. The order in which
the data will be written to the netCDF variable is with the last
dimension of the specified variable varying fastest. If the type of
data values differs from the netCDF variable type, type conversion
will occur. @xref{Type Conversion,,, netcdf, @value{n-man}}.

@end table

@heading Return Codes

@itemize

@item NC_NOERR
No error.

@item NC_EHDFERR
Error reported by HDF5 layer.

@item NC_ENOTVAR
The variable ID is invalid for the specified netCDF dataset. 

@item NC_EINVALCOORDS
The specified corner indices were out of range for the rank of the
specified variable. For example, a negative index, or an index that is
larger than the corresponding dimension length will cause an error.

@item NC_EEDGE
The specified edge lengths added to the specified corner would have
referenced data out of range for the rank of the specified
variable. For example, an edge length that is larger than the
corresponding dimension length minus the corner index will cause an
error.

@item NC_ERANGE
One or more of the specified values are out of the range of values
representable by the external data type of the variable. (Does not
apply to the nc_put_vara() function).

@item NC_EINDEFINE
The specified netCDF dataset is in define mode rather than data mode. 

@item NC_EBADID
The specified netCDF ID does not refer to an open netCDF dataset. 

@item NC_ECHAR
Attempt to convert to or from char.

@item NC_ENOMEM
Out of memory.

@item NC_EBADTYPE
Bad type.

@end itemize

@heading Example

Here is an example using nc_put_vara_double to add or change all the
values of the variable named rh to 0.5 in an existing netCDF dataset
named foo.nc. For simplicity in this example, we assume that we know
that rh is dimensioned with time, lat, and lon, and that there are
three time values, five lat values, and ten lon values.

@example
#include <netcdf.h>
   ... 
#define TIMES 3
#define LATS  5
#define LONS  10
int  status;                       /* error status */
int  ncid;                         /* netCDF ID */
int  rh_id;                        /* variable ID */
static size_t start[] = @{0, 0, 0@}; /* start at first value */
static size_t count[] = @{TIMES, LATS, LONS@};
double rh_vals[TIMES*LATS*LONS];   /* array to hold values */
int i;
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
for (i = 0; i < TIMES*LATS*LONS; i++)
    rh_vals[i] = 0.5;
/* write values into netCDF variable */
status = nc_put_vara_double(ncid, rh_id, start, count, rh_vals);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_put_vars_ type, nc_put_varm_ type, nc_put_vara_ type, Variables
@section Write a Subsampled Array of Values: nc_put_vars_ @var{type} 
@findex nc_put_vars_ type
@cindex nc_put_vars_ type, example
@cindex writing subsampled array
@cindex subsampled array, writing
@findex nc_put_vars_text  
@findex nc_put_vars_uchar 
@findex nc_put_vars_schar 
@findex nc_put_vars_short 
@findex nc_put_vars_int   
@findex nc_put_vars_long  
@findex nc_put_vars_float 
@findex nc_put_vars_double
@findex nc_put_vars_ushort
@findex nc_put_vars_uint  
@findex nc_put_vars_longlong 
@findex nc_put_vars_ulonglong
@findex nc_put_vars_string
@findex nc_put_vars       


Each member of the family of functions nc_put_vars_ @var{type} writes a
subsampled (strided) array section of values into a netCDF variable of
an open netCDF dataset. The subsampled array section is specified by
giving a corner, a vector of counts, and a stride vector. The netCDF
dataset must be in data mode.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and
string are only available for netCDF-4/HDF5 files.

The nc_put_vars() function will write a variable of any type,
including user defined type. For this function, the type of the data
in memory must match the type of the variable - no data conversion is
done.

@heading Usage 
@example
int nc_put_vars_text  (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const char *tp);
int nc_put_vars_uchar (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const unsigned char *up);
int nc_put_vars_schar (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const signed char *cp);
int nc_put_vars_short (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const short *sp);
int nc_put_vars_int   (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const int *ip);
int nc_put_vars_long  (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const long *lp);
int nc_put_vars_float (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const float *fp);
int nc_put_vars_double(int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const double *dp);
int nc_put_vars_ushort(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const unsigned short *op);
int nc_put_vars_uint  (int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const unsigned int *op);
int nc_put_vars_longlong (int ncid, int varid, const size_t *startp, 
                          const size_t *countp, const ptrdiff_t *stridep, 
                          const long long *op);
int nc_put_vars_ulonglong(int ncid, int varid, const size_t *startp, 
                          const size_t *countp, const ptrdiff_t *stridep, 
                          const unsigned long long *op);
int nc_put_vars_string(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const char **op);
int nc_put_vars       (int ncid, int varid,  const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep,
                       const void *op);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.
 
@item start
A vector of size_t integers specifying the index in the variable
where the first of the data values will be written. The indices are
relative to 0, so for example, the first data value of a variable
would have index (0, 0, ... , 0). The elements of start correspond, in
order, to the variable's dimensions. Hence, if the variable is a
record variable, the first index corresponds to the starting record
number for writing the data values.
 
@item count
A vector of size_t integers specifying the number of indices selected
along each dimension. To write a single value, for example, specify
count as (1, 1, ... , 1). The elements of count correspond, in order,
to the variable's dimensions. Hence, if the variable is a record
variable, the first element of count corresponds to a count of the
number of records to write.

Note: setting any element of the count array to zero causes the
function to exit without error, and without doing anything.
 
@item stride
A vector of ptrdiff_t integers that specifies the sampling interval
along each dimension of the netCDF variable. The elements of the
stride vector correspond, in order, to the netCDF variable's
dimensions (stride[0] gives the sampling interval along the most
slowly varying dimension of the netCDF variable). Sampling intervals
are specified in type-independent units of elements (a value of 1
selects consecutive elements of the netCDF variable along the
corresponding dimension, a value of 2 selects every other element,
etc.). A NULL stride argument is treated as (1, 1, ... , 1).
 
@item tp
@itemx up
@itemx cp
@itemx sp
@itemx ip
@itemx lp
@itemx fp
@itemx dp
Pointer to a block of contiguous data values to be written. The order in which
the data will be written to the netCDF variable is with the last
dimension of the specified variable varying fastest. If the type of
data values differs from the netCDF variable type, type conversion
will occur. @xref{Type Conversion,,, netcdf, @value{n-man}}.

@end table

@heading Return Codes

@itemize

@item NC_NOERR
No error.

@item NC_EHDFERR
Error reported by HDF5 layer.

@item NC_ENOTVAR
The variable ID is invalid for the specified netCDF dataset. 

@item NC_EINVALCOORDS
The specified corner indices were out of range for the rank of the
specified variable. For example, a negative index, or an index that is
larger than the corresponding dimension length will cause an error.

@item NC_EEDGE
The specified edge lengths added to the specified corner would have
referenced data out of range for the rank of the specified
variable. For example, an edge length that is larger than the
corresponding dimension length minus the corner index will cause an
error.

@item NC_ERANGE
One or more of the specified values are out of the range of values
representable by the external data type of the variable. (Does not
apply to the nc_put_vars() function).

@item NC_EINDEFINE
The specified netCDF dataset is in define mode rather than data mode. 

@item NC_EBADID
The specified netCDF ID does not refer to an open netCDF dataset. 

@item NC_ECHAR
Attempt to convert to or from char.

@item NC_ENOMEM
Out of memory.

@item NC_EBADTYPE
Bad type.

@end itemize

@heading Example

Here is an example of using nc_put_vars_float to write -- from an
internal array -- every other point of a netCDF variable named rh
which is described by the C declaration float rh[4][6] (note the size
of the dimensions):

@example
#include <netcdf.h>
   ... 
#define NDIM 2                /* rank of netCDF variable */
int ncid;                     /* netCDF ID */
int status;                   /* error status */
int rhid;                     /* variable ID */
static size_t start[NDIM]     /* netCDF variable start point: */
                 = @{0, 0@};    /* first element */
static size_t count[NDIM]     /* size of internal array: entire */
                   = @{2, 3@};  /* (subsampled) netCDF variable */
static ptrdiff_t stride[NDIM] /* variable subsampling intervals: */
                 = @{2, 2@};    /* access every other netCDF element */
float rh[2][3];               /* note subsampled sizes for */
                              /* netCDF variable dimensions */
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid(ncid, "rh", &rhid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_put_vars_float(ncid, rhid, start, count, stride, rh);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_put_varm_ type, nc_get_var1_ type, nc_put_vars_ type, Variables
@section Write a Mapped Array of Values: nc_put_varm_ @var{type} 
@findex nc_put_varm_ type
@cindex nc_put_varm_ type, example
@cindex array, writing mapped
@cindex writing mapped array
@cindex mapped array, writing
@findex nc_put_varm_text  
@findex nc_put_varm_uchar 
@findex nc_put_varm_schar 
@findex nc_put_varm_short 
@findex nc_put_varm_int   
@findex nc_put_varm_long  
@findex nc_put_varm_float 
@findex nc_put_varm_double
@findex nc_put_varm_ushort
@findex nc_put_varm_uint  
@findex nc_put_varm_longlong 
@findex nc_put_varm_ulonglong
@findex nc_put_varm_string
@findex nc_put_varm       

The nc_put_varm_ @var{type} family of functions writes a mapped array
section of values into a netCDF variable of an open netCDF
dataset. The mapped array section is specified by giving a corner, a
vector of counts, a stride vector, and an index mapping vector. The
index mapping vector is a vector of integers that specifies the
mapping between the dimensions of a netCDF variable and the in-memory
structure of the internal data array. No assumptions are made about
the ordering or length of the dimensions of the data array. The netCDF
dataset must be in data mode.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and
string are only available for netCDF-4/HDF5 files.

The nc_put_varm() function will write a variable of any type,
including user defined type. For this function, the type of the data
in memory must match the type of the variable - no data conversion is
done.

@heading Usage 
@example
int nc_put_varm_text  (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], const char *tp);
int nc_put_varm_uchar (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], const unsigned char *up);
int nc_put_varm_schar (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], const signed char *cp);
int nc_put_varm_short (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], const short *sp);
int nc_put_varm_int   (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], const int *ip);
int nc_put_varm_long  (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], const long *lp);
int nc_put_varm_float (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], const float *fp);
int nc_put_varm_double(int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], const double *dp);
int nc_put_varm_ushort(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const ptrdiff_t * imapp, const unsigned short *op);
int nc_put_varm_uint  (int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const ptrdiff_t * imapp, const unsigned int *op);
int nc_put_varm_longlong (int ncid, int varid, const size_t *startp, 
                          const size_t *countp, const ptrdiff_t *stridep, 
                          const ptrdiff_t * imapp, const long long *op);
int nc_put_varm_ulonglong(int ncid, int varid, const size_t *startp, 
                          const size_t *countp, const ptrdiff_t *stridep, 
                          const ptrdiff_t * imapp, const unsigned long long *op);
int nc_put_varm_string(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const ptrdiff_t * imapp, const char **op);
int nc_put_varm       (int ncid, int varid,  const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, const void *op);
n@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.
 
@item start
A vector of size_t integers specifying the index in the variable
where the first of the data values will be written. The indices are
relative to 0, so for example, the first data value of a variable
would have index (0, 0, ... , 0). The elements of start correspond, in
order, to the variable's dimensions. Hence, if the variable is a
record variable, the first index corresponds to the starting record
number for writing the data values.
 
@item count
A vector of size_t integers specifying the number of indices selected
along each dimension. To write a single value, for example, specify
count as (1, 1, ... , 1). The elements of count correspond, in order,
to the variable's dimensions. Hence, if the variable is a record
variable, the first element of count corresponds to a count of the
number of records to write.

Note: setting any element of the count array to zero causes the
function to exit without error, and without doing anything.
 
@item stride
A vector of ptrdiff_t integers that specifies the sampling interval
along each dimension of the netCDF variable. The elements of the
stride vector correspond, in order, to the netCDF variable's
dimensions (stride[0] gives the sampling interval along the most
slowly varying dimension of the netCDF variable). Sampling intervals
are specified in type-independent units of elements (a value of 1
selects consecutive elements of the netCDF variable along the
corresponding dimension, a value of 2 selects every other element,
etc.). A NULL stride argument is treated as (1, 1, ... , 1).
 
@item imap
A vector of ptrdiff_t integers that specifies the mapping between the
dimensions of a netCDF variable and the in-memory structure of the
internal data array. The elements of the index mapping vector
correspond, in order, to the netCDF variable's dimensions (imap[0]
gives the distance between elements of the internal array
corresponding to the most slowly varying dimension of the netCDF
variable). Distances between elements are specified in
type-independent units of elements (the distance between internal
elements that occupy adjacent memory locations is 1 and not the
element's byte-length as in netCDF 2). A NULL argument means the
memory-resident values have the same structure as the associated
netCDF variable.
 
@item tp
@itemx up
@itemx cp
@itemx sp
@itemx ip
@itemx lp
@itemx fp
@itemx dp
Pointer to the location used for computing where the data values will
be found; the data should be of the type appropriate for the function
called. If the type of data values differs from the netCDF variable
type, type conversion will occur. @xref{Type Conversion,,, netcdf, @value{n-man}}.

@end table
 
@heading Return Codes

@itemize

@item NC_NOERR
No error.

@item NC_EHDFERR
Error reported by HDF5 layer.

@item NC_ENOTVAR
The variable ID is invalid for the specified netCDF dataset. 

@item NC_EINVALCOORDS
The specified corner indices were out of range for the rank of the
specified variable. For example, a negative index, or an index that is
larger than the corresponding dimension length will cause an error.

@item NC_EEDGE
The specified edge lengths added to the specified corner would have
referenced data out of range for the rank of the specified
variable. For example, an edge length that is larger than the
corresponding dimension length minus the corner index will cause an
error.

@item NC_ERANGE
One or more of the specified values are out of the range of values
representable by the external data type of the variable. (Does not
apply to the nc_put_vars() function).

@item NC_EINDEFINE
The specified netCDF dataset is in define mode rather than data mode. 

@item NC_EBADID
The specified netCDF ID does not refer to an open netCDF dataset. 

@item NC_ECHAR
Attempt to convert to or from char.

@item NC_ENOMEM
Out of memory.

@end itemize

@heading Example

The following imap vector maps in the trivial way a 4x3x2 netCDF
variable and an internal array of the same shape:

@example
float a[4][3][2];       /* same shape as netCDF variable */
int   imap[3] = @{6, 2, 1@};
                        /* netCDF dimension       inter-element distance */
                        /* ----------------       ---------------------- */
                        /* most rapidly varying       1                  */
                        /* intermediate               2 (=imap[2]*2)     */
                        /* most slowly varying        6 (=imap[1]*3)     */
@end example

Using the imap vector above with nc_put_varm_float obtains the same
result as simply using nc_put_var_float.

Here is an example of using nc_put_varm_float to write -- from a
transposed, internal array -- a netCDF variable named rh which is
described by the C declaration float rh[6][4] (note the size and order
of the dimensions):

@example
#include <netcdf.h>
   ... 
#define NDIM 2               /* rank of netCDF variable */
int ncid;                    /* netCDF ID */
int status;                  /* error status */
int rhid;                    /* variable ID */
static size_t start[NDIM]    /* netCDF variable start point: */
                 = @{0, 0@};   /* first element */
static size_t count[NDIM]    /* size of internal array: entire netCDF */
                 = @{6, 4@};   /* variable; order corresponds to netCDF */
                             /* variable -- not internal array */
static ptrdiff_t stride[NDIM]/* variable subsampling intervals: */
                 = @{1, 1@};   /* sample every netCDF element */
static ptrdiff_t imap[NDIM]  /* internal array inter-element distances; */
                 = @{1, 6@};   /* would be @{4, 1@} if not transposing */
float rh[4][6];              /* note transposition of netCDF variable */
                             /* dimensions */
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid(ncid, "rh", &rhid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_put_varm_float(ncid, rhid, start, count, stride, imap, rh);
if (status != NC_NOERR) handle_error(status);
@end example

Here is another example of using nc_put_varm_float to write -- from a
transposed, internal array -- a subsample of the same netCDF variable,
by writing every other point of the netCDF variable:

@example
#include <netcdf.h>
   ... 
#define NDIM 2                /* rank of netCDF variable */
int ncid;                     /* netCDF ID */
int status;                   /* error status */
int rhid;                     /* variable ID */
static size_t start[NDIM]     /* netCDF variable start point: */
                 = @{0, 0@};    /* first element */
static size_t count[NDIM]     /* size of internal array: entire */
                   = @{3, 2@};  /* (subsampled) netCDF variable; order of */
                              /* dimensions corresponds to netCDF */
                              /* variable -- not internal array */
static ptrdiff_t stride[NDIM] /* variable subsampling intervals: */
                 = @{2, 2@};    /* sample every other netCDF element */
static ptrdiff_t imap[NDIM]   /* internal array inter-element distances; */
                 = @{1, 3@};    /* would be @{2, 1@} if not transposing */
float rh[2][3];               /* note transposition of (subsampled) */
                              /* netCDF variable dimensions */
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid(ncid, "rh", &rhid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_put_varm_float(ncid, rhid, start, count, stride, imap, rh);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_get_var1_ type, nc_get_var_ type, nc_put_varm_ type, Variables
@section Read a Single Data Value: nc_get_var1_ @var{type} 
@findex nc_get_var1_ type
@cindex nc_get_var1_ type, example
@cindex reading single value
@cindex single value, reading
@findex nc_get_var1_text  
@findex nc_get_var1_uchar 
@findex nc_get_var1_schar 
@findex nc_get_var1_short 
@findex nc_get_var1_int   
@findex nc_get_var1_long  
@findex nc_get_var1_float 
@findex nc_get_var1_double
@findex nc_get_var1_ushort
@findex nc_get_var1_uint  
@findex nc_get_var1_longlong 
@findex nc_get_var1_ulonglong
@findex nc_get_var1_string
@findex nc_get_var1       

The functions nc_get_var1_ @var{type} get a single data value from a
variable of an open netCDF dataset that is in data mode. Inputs are
the netCDF ID, the variable ID, a multidimensional index that
specifies which value to get, and the address of a location into which
the data value will be read. The value is converted from the external
data type of the variable, if necessary.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and
string are only available for netCDF-4/HDF5 files.

The nc_get_var1() function will read a variable of any type,
including user defined type. For this function, the type of the data
in memory must match the type of the variable - no data conversion is
done.

@heading Usage 
@example
int nc_get_var1_text  (int ncid, int varid, const size_t index[],
                       char *tp);
int nc_get_var1_uchar (int ncid, int varid, const size_t index[],
                       unsigned char *up);
int nc_get_var1_schar (int ncid, int varid, const size_t index[],
                       signed char *cp);
int nc_get_var1_short (int ncid, int varid, const size_t index[],
                       short *sp);
int nc_get_var1_int   (int ncid, int varid, const size_t index[],
                       int *ip);
int nc_get_var1_long  (int ncid, int varid, const size_t index[],
                       long *lp);
int nc_get_var1_float (int ncid, int varid, const size_t index[],
                       float *fp); 
int nc_get_var1_double(int ncid, int varid, const size_t index[],
                       double *dp);
int nc_get_var1_ushort(int ncid, int varid, const size_t *indexp, 
                       unsigned short *ip);
int nc_get_var1_uint  (int ncid, int varid, const size_t *indexp, 
                       unsigned int *ip);
int nc_get_var1_longlong (int ncid, int varid, const size_t *indexp, 
                          long long *ip);
int nc_get_var1_ulonglong(int ncid, int varid, const size_t *indexp, 
                          unsigned long long *ip);
int nc_get_var1_string(int ncid, int varid, const size_t *indexp, 
                       char **ip);
int nc_get_var1       (int ncid, int varid,  const size_t *indexp,
                       void *ip);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.
 
@item index[]
The index of the data value to be read. The indices are relative to
0, so for example, the first data value of a two-dimensional variable
would have index (0,0). The elements of index must correspond to the
variable's dimensions. Hence, if the variable is a record variable,
the first index is the record number.
 
@item tp
@itemx up
@itemx cp
@itemx sp
@itemx ip
@itemx lp
@itemx fp
@itemx dp
Pointer to the location into which the data value is read. If the type
of data value differs from the netCDF variable type, type conversion
will occur. @xref{Type Conversion,,, netcdf, @value{n-man}}.

@end table

@heading Return Codes

@itemize

@item NC_NOERR
No error.

@item NC_EHDFERR
Error reported by HDF5 layer.

@item NC_ENOTVAR
The variable ID is invalid for the specified netCDF dataset. 

@item NC_EINVALCOORDS
The specified corner indices were out of range for the rank of the
specified variable. For example, a negative index, or an index that is
larger than the corresponding dimension length will cause an error.

@item NC_EEDGE
The specified edge lengths added to the specified corner would have
referenced data out of range for the rank of the specified
variable. For example, an edge length that is larger than the
corresponding dimension length minus the corner index will cause an
error.

@item NC_ERANGE
One or more of the specified values are out of the range of values
representable by the external data type of the variable. (Does not
apply to the nc_put_vars() function).

@item NC_EINDEFINE
The specified netCDF is in define mode rather than data mode. 

@item NC_EBADID
The specified netCDF ID does not refer to an open netCDF dataset. 

@item NC_ECHAR
Attempt to convert to or from char.

@item NC_ENOMEM
Out of memory.

@end itemize

@heading Example

Here is an example using nc_get_var1_double to get the (1,2,3) element
of the variable named rh in an existing netCDF dataset named
foo.nc. For simplicity in this example, we assume that we know that rh
is dimensioned with time, lat, and lon, so we want to get the value of
rh that corresponds to the second time value, the third lat value, and
the fourth lon value:

@example
#include <netcdf.h>
   ... 
int  status;                           /* error status */
int ncid;                              /* netCDF ID */
int rh_id;                             /* variable ID */
static size_t rh_index[] = @{1, 2, 3@};  /* where to get value from */
double rh_val;                         /* where to put it */
   ... 
status = nc_open("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_get_var1_double(ncid, rh_id, rh_index, &rh_val);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_get_var_ type, nc_get_vara_ type, nc_get_var1_ type, Variables
@section Read an Entire Variable nc_get_var_ @var{type} 
@findex nc_get_var_ type
@cindex nc_get_var_ type, example
@cindex reading entire variable
@cindex entire variable, reading
@findex nc_get_var_text  
@findex nc_get_var_uchar 
@findex nc_get_var_schar 
@findex nc_get_var_short 
@findex nc_get_var_int   
@findex nc_get_var_long  
@findex nc_get_var_float 
@findex nc_get_var_double
@findex nc_get_var_ushort
@findex nc_get_var_uint  
@findex nc_get_var_longlong 
@findex nc_get_var_ulonglong
@findex nc_get_var_string
@findex nc_get_var       

The members of the nc_get_var_ @var{type} family of functions read all the
values from a netCDF variable of an open netCDF dataset. This is the
simplest interface to use for reading the value of a scalar variable
or when all the values of a multidimensional variable can be read at
once. The values are read into consecutive locations with the last
dimension varying fastest. The netCDF dataset must be in data mode.

Take care when using the simplest forms of this interface with record
variables (variables that use the NC_UNLIMITED dimension) when you
don't specify how many records are to be read. If you try to read all
the values of a record variable into an array but there are more
records in the file than you assume, more data will be read than you
expect, which may cause a segmentation violation. To avoid such
problems, it is better to use the nc_get_vara interfaces for
variables that use the NC_UNLIMITED dimension.  @xref{nc_get_vara_
type}. 

The functions for types ubyte, ushort, uint, longlong, ulonglong, and
string are only available for netCDF-4/HDF5 files.

The nc_get_var() function will read a variable of any type,
including user defined type. For this function, the type of the data
in memory must match the type of the variable - no data conversion is
done.

@heading Usage 
@example
int nc_get_var_text  (int ncid, int varid, char *tp);
int nc_get_var_uchar (int ncid, int varid, unsigned char *up);
int nc_get_var_schar (int ncid, int varid, signed char *cp);
int nc_get_var_short (int ncid, int varid, short *sp);
int nc_get_var_int   (int ncid, int varid, int *ip);
int nc_get_var_long  (int ncid, int varid, long *lp);
int nc_get_var_float (int ncid, int varid, float *fp);
int nc_get_var_double(int ncid, int varid, double *dp);
int nc_get_var_ushort(int ncid, int varid, unsigned short *ip);
int nc_get_var_uint  (int ncid, int varid, unsigned int *ip);
int nc_get_var_longlong (int ncid, int varid, long long *ip);
int nc_get_var_ulonglong(int ncid, int varid, unsigned long long *ip);
int nc_get_var_string(int ncid, int varid, char **ip);
int nc_get_var       (int ncid, int varid,  void *ip);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.
 
@item tp
@itemx up
@itemx cp
@itemx sp
@itemx ip
@itemx lp
@itemx fp
@itemx dp
Pointer to a block of contiguous locations in memory into which the data values are read. If the type
of data value differs from the netCDF variable type, type conversion
will occur. @xref{Type Conversion,,, netcdf, @value{n-man}}.

@end table

@heading Return Codes 

@itemize

@item NC_NOERR
No error.

@item NC_EHDFERR
Error reported by HDF5 layer.

@item NC_ENOTVAR
The variable ID is invalid for the specified netCDF dataset. 

@item NC_EINVALCOORDS
The specified corner indices were out of range for the rank of the
specified variable. For example, a negative index, or an index that is
larger than the corresponding dimension length will cause an error.

@item NC_EEDGE
The specified edge lengths added to the specified corner would have
referenced data out of range for the rank of the specified
variable. For example, an edge length that is larger than the
corresponding dimension length minus the corner index will cause an
error.

@item NC_ERANGE
One or more of the specified values are out of the range of values
representable by the external data type of the variable. (Does not
apply to the nc_put_vars() function).

@item NC_EINDEFINE
The specified netCDF is in define mode rather than data mode. 

@item NC_EBADID
The specified netCDF ID does not refer to an open netCDF dataset. 

@item NC_ECHAR
Attempt to convert to or from char.

@item NC_ENOMEM
Out of memory.

@end itemize

@heading Example

Here is an example using nc_get_var_double to read all the values of
the variable named rh from an existing netCDF dataset named
foo.nc. For simplicity in this example, we assume that we know that rh
is dimensioned with lat and lon, and that there are five lat values
and ten lon values.

@example
#include <netcdf.h>
   ... 
#define LATS 5
#define LONS 10
int  status;                       /* error status */
int ncid;                          /* netCDF ID */
int rh_id;                         /* variable ID */
double rh_vals[LATS*LONS];         /* array to hold values */
   ... 
status = nc_open("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
/* read values from netCDF variable */
status = nc_get_var_double(ncid, rh_id, rh_vals);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_get_vara_ type, nc_get_vars_ type, nc_get_var_ type, Variables
@section Read an Array of Values: nc_get_vara_ @var{type} 
@findex nc_get_vara_ type
@cindex nc_get_vara_ type, example
@cindex array section, reading mapped
@cindex array section, writing mapped
@findex nc_get_vara_text  
@findex nc_get_vara_uchar 
@findex nc_get_vara_schar 
@findex nc_get_vara_short 
@findex nc_get_vara_int   
@findex nc_get_vara_long  
@findex nc_get_vara_float 
@findex nc_get_vara_double
@findex nc_get_vara_ushort
@findex nc_get_vara_uint  
@findex nc_get_vara_longlong
@findex nc_get_vara_ulonglong
@findex nc_get_vara_string
@findex nc_get_vara       

The members of the nc_get_vara_ @var{type} family of functions read an array
of values from a netCDF variable of an open netCDF dataset. The array
is specified by giving a corner and a vector of edge lengths. The
values are read into consecutive locations with the last dimension
varying fastest. The netCDF dataset must be in data mode.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and
string are only available for netCDF-4/HDF5 files.

The nc_get_vara() function will write a variable of any type,
including user defined type. For this function, the type of the data
in memory must match the type of the variable - no data conversion is
done.

@heading Usage 
@example
int nc_get_vara_text  (int ncid, int varid, const size_t start[],
                       const size_t count[], char *tp);
int nc_get_vara_uchar (int ncid, int varid, const size_t start[],
                       const size_t count[], unsigned char *up);
int nc_get_vara_schar (int ncid, int varid, const size_t start[],
                       const size_t count[], signed char *cp);
int nc_get_vara_short (int ncid, int varid, const size_t start[],
                       const size_t count[], short *sp);
int nc_get_vara_int   (int ncid, int varid, const size_t start[],
                       const size_t count[], int *ip);
int nc_get_vara_long  (int ncid, int varid, const size_t start[],
                       const size_t count[], long *lp);
int nc_get_vara_float (int ncid, int varid, const size_t start[],
                       const size_t count[], float *fp);
int nc_get_vara_double(int ncid, int varid, const size_t start[],
                       const size_t count[], double *dp);
int nc_get_vara_ushort(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, unsigned short *ip);
int nc_get_vara_uint  (int ncid, int varid, const size_t *startp, 
                       const size_t *countp, unsigned int *ip);
int nc_get_vara_longlong(int ncid, int varid, const size_t *startp, 
                         const size_t *countp, long long *ip);
int nc_get_vara_ulonglong(int ncid, int varid, const size_t *startp, 
                          const size_t *countp, unsigned long long *ip);
int nc_get_vara_string(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, char **ip);
int nc_get_vara       (int ncid, int varid, const size_t start[], 
                       const size_t count[], void *ip);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.
 
@item start
A vector of size_t integers specifying the index in the variable
where the first of the data values will be read. The indices are
relative to 0, so for example, the first data value of a variable
would have index (0, 0, ... , 0). The length of start must be the same
as the number of dimensions of the specified variable. The elements of
start correspond, in order, to the variable's dimensions. Hence, if
the variable is a record variable, the first index would correspond to
the starting record number for reading the data values.
 
@item count
A vector of size_t integers specifying the edge lengths along each
dimension of the block of data values to be read. To read a single
value, for example, specify count as (1, 1, ... , 1). The length of
count is the number of dimensions of the specified variable. The
elements of count correspond, in order, to the variable's
dimensions. Hence, if the variable is a record variable, the first
element of count corresponds to a count of the number of records to
read.

Note: setting any element of the count array to zero causes the
function to exit without error, and without doing anything.

@item tp
@itemx up
@itemx cp
@itemx sp
@itemx ip
@itemx lp
@itemx fp
@itemx dp
Pointer to a block of contiguous locations in memory into which the data values are read.
If the type
of data value differs from the netCDF variable type, type conversion
will occur. @xref{Type Conversion,,, netcdf, @value{n-man}}.

@end table
 
@heading Return Codes

@itemize

@item NC_NOERR
No error.

@item NC_ENOTVAR
The variable ID is invalid for the specified netCDF dataset. 

@item NC_EINVALCOORDS
The specified corner indices were out of range for the rank of the
specified variable. For example, a negative index or an index that is
larger than the corresponding dimension length will cause an error.

@item NC_EEDGE
The specified edge lengths added to the specified corner would have
referenced data out of range for the rank of the specified
variable. For example, an edge length that is larger than the
corresponding dimension length minus the corner index will cause an
error.

@item NC_ERANGE
One or more of the values are out of the range of values representable
by the desired type. (Does not apply to nc_get_vara() function).

@item NC_EINDEFINE
The specified netCDF is in define mode rather than data mode. 

@item NC_EBADID
The specified netCDF ID does not refer to an open netCDF dataset. 
@end itemize

@heading Example

Here is an example using nc_get_vara_double to read all the values of
the variable named rh from an existing netCDF dataset named
foo.nc. For simplicity in this example, we assume that we know that rh
is dimensioned with time, lat, and lon, and that there are three time
values, five lat values, and ten lon values.

@example
#include <netcdf.h>
   ... 
#define TIMES 3
 #define LATS 5
#define LONS 10
int  status;                       /* error status */
int ncid;                          /* netCDF ID */
int rh_id;                         /* variable ID */
static size_t start[] = @{0, 0, 0@}; /* start at first value */
static size_t count[] = @{TIMES, LATS, LONS@};
double rh_vals[TIMES*LATS*LONS];   /* array to hold values */
   ... 
status = nc_open("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
/* read values from netCDF variable */
status = nc_get_vara_double(ncid, rh_id, start, count, rh_vals);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_get_vars_ type, nc_get_varm_ type, nc_get_vara_ type, Variables
@section Read a Subsampled Array of Values: nc_get_vars_ @var{type} 
@findex nc_get_vars_ type
@cindex nc_get_vars_ type, example
@cindex array section, writing subsampled
@cindex array section, reading subsampled
@findex nc_get_vars_text  
@findex nc_get_vars_uchar 
@findex nc_get_vars_schar 
@findex nc_get_vars_short 
@findex nc_get_vars_int   
@findex nc_get_vars_long  
@findex nc_get_vars_float 
@findex nc_get_vars_double
@findex nc_get_vars_ushort
@findex nc_get_vars_uint  
@findex nc_get_vars_longlong 
@findex nc_get_vars_ulonglong
@findex nc_get_vars_string
@findex nc_get_vars       

The nc_get_vars_ @var{type} family of functions read a subsampled (strided)
array section of values from a netCDF variable of an open netCDF
dataset. The subsampled array section is specified by giving a corner,
a vector of edge lengths, and a stride vector. The values are read
with the last dimension of the netCDF variable varying fastest. The
netCDF dataset must be in data mode.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and
string are only available for netCDF-4/HDF5 files.

The nc_get_vars() function will read a variable of any type,
including user defined type. For this function, the type of the data
in memory must match the type of the variable - no data conversion is
done.

@heading Usage 
@example
int nc_get_vars_text  (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       char *tp);
int nc_get_vars_uchar (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       unsigned char *up);
int nc_get_vars_schar (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       signed char *cp);
int nc_get_vars_short (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       short *sp);
int nc_get_vars_int   (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       int *ip);
int nc_get_vars_long  (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       long *lp);
int nc_get_vars_float (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       float *fp);
int nc_get_vars_double(int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       double *dp)
int nc_get_vars_ushort(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       unsigned short *ip);
int nc_get_vars_uint  (int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       unsigned int *ip);
int nc_get_vars_longlong (int ncid, int varid, const size_t *startp, 
                          const size_t *countp, const ptrdiff_t *stridep, 
                          long long *ip);
int nc_get_vars_ulonglong(int ncid, int varid, const size_t *startp, 
                          const size_t *countp, const ptrdiff_t *stridep, 
                          unsigned long long *ip);
int nc_get_vars_string(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       char **ip);
int nc_get_vars       (int ncid, int varid,  const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep,
                       void *ip);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.
 
@item start
A vector of size_t integers specifying the index in the variable
where the first of the data values will be read. The indices are
relative to 0, so for example, the first data value of a variable
would have index (0, 0, ... , 0). The elements of start correspond, in
order, to the variable's dimensions. Hence, if the variable is a
record variable, the first index corresponds to the starting record
number for reading the data values.
 
@item count
A vector of size_t integers specifying the number of indices selected
along each dimension. To read a single value, for example, specify
count as (1, 1, ... , 1). The elements of count correspond, in order,
to the variable's dimensions. Hence, if the variable is a record
variable, the first element of count corresponds to a count of the
number of records to read.
 
Note: setting any element of the count array to zero causes the
function to exit without error, and without doing anything.

@item stride
A vector of ptrdiff_t integers specifying, for each dimension, the
interval between selected indices. The elements of the stride vector
correspond, in order, to the variable's dimensions. A value of 1
accesses adjacent values of the netCDF variable in the corresponding
dimension; a value of 2 accesses every other value of the netCDF
variable in the corresponding dimension; and so on. A NULL stride
argument is treated as (1, 1, ... , 1).
 
@item tp
@itemx up
@itemx cp
@itemx sp
@itemx ip
@itemx lp
@itemx fp
@itemx dp
Pointer to a block of contiguous locations in memory into which the data values are read.
If the type
of data value differs from the netCDF variable type, type conversion
will occur. @xref{Type Conversion,,, netcdf, @value{n-man}}.

@end table

@heading Return Codes

@itemize

@item NC_NOERR
No error.

@item NC_EHDFERR
Error reported by HDF5 layer.

@item NC_ENOTVAR
The variable ID is invalid for the specified netCDF dataset. 

@item NC_EINVALCOORDS
The specified corner indices were out of range for the rank of the
specified variable. For example, a negative index, or an index that is
larger than the corresponding dimension length will cause an error.

@item NC_EEDGE
The specified edge lengths added to the specified corner would have
referenced data out of range for the rank of the specified
variable. For example, an edge length that is larger than the
corresponding dimension length minus the corner index will cause an
error.

@item NC_ERANGE
One or more of the specified values are out of the range of values
representable by the external data type of the variable. (Does not
apply to the nc_get_vars() function).

@item NC_EINDEFINE
The specified netCDF is in define mode rather than data mode. 

@item NC_EBADID
The specified netCDF ID does not refer to an open netCDF dataset. 

@item NC_ECHAR
Attempt to convert to or from char.

@item NC_ENOMEM
Out of memory.

@end itemize

@heading Example

Here is an example that uses nc_get_vars_double to read every other
value in each dimension of the variable named rh from an existing
netCDF dataset named foo.nc. For simplicity in this example, we assume
that we know that rh is dimensioned with time, lat, and lon, and that
there are three time values, five lat values, and ten lon values.

@example
#include <netcdf.h>
   ... 
#define TIMES 3
#define LATS  5
#define LONS 10
int  status;                          /* error status */
int ncid;                             /* netCDF ID */
int rh_id;                            /* variable ID */
static size_t start[] = @{0, 0, 0@};    /* start at first value */
static size_t count[] = @{TIMES, LATS, LONS@};
static ptrdiff_t stride[] = @{2, 2, 2@};/* every other value */
double data[TIMES][LATS][LONS];       /* array to hold values */
 ... 
status = nc_open("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
 ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
 ... 
/* read subsampled values from netCDF variable into array */
status = nc_get_vars_double(ncid, rh_id, start, count, stride, 
                            &data[0][0][0]);
if (status != NC_NOERR) handle_error(status);
 ... 
@end example

@node nc_get_varm_ type, Strings, nc_get_vars_ type, Variables
@section Read a Mapped Array of Values: nc_get_varm_ @var{type} 
@findex nc_get_varm_ type
@cindex nc_get_varm_ type, example
@cindex writing mapped array section
@cindex mapped array section, writing
@findex nc_get_varm_text  
@findex nc_get_varm_uchar 
@findex nc_get_varm_schar 
@findex nc_get_varm_short 
@findex nc_get_varm_int   
@findex nc_get_varm_long  
@findex nc_get_varm_float 
@findex nc_get_varm_double
@findex nc_get_varm_ushort
@findex nc_get_varm_uint  
@findex nc_get_varm_longlong 
@findex nc_get_varm_ulonglong
@findex nc_get_varm_string
@findex nc_get_varm       


The nc_get_varm_ @var{type} family of functions reads a mapped array section
of values from a netCDF variable of an open netCDF dataset. The mapped
array section is specified by giving a corner, a vector of edge
lengths, a stride vector, and an index mapping vector. The index
mapping vector is a vector of integers that specifies the mapping
between the dimensions of a netCDF variable and the in-memory
structure of the internal data array. No assumptions are made about
the ordering or length of the dimensions of the data array. The netCDF
dataset must be in data mode.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and
string are only available for netCDF-4/HDF5 files.

The nc_get_varm() function will read a variable of any type,
including user defined type. For this function, the type of the data
in memory must match the type of the variable - no data conversion is
done.

@heading Usage 
@example
int nc_get_varm_text  (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], char *tp);
int nc_get_varm_uchar (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], unsigned char *up);
int nc_get_varm_schar (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], signed char *cp);
int nc_get_varm_short (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], short *sp);
int nc_get_varm_int   (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], int *ip);
int nc_get_varm_long  (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], long *lp);
int nc_get_varm_float (int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], float *fp);
int nc_get_varm_double(int ncid, int varid, const size_t start[],
                       const size_t count[], const ptrdiff_t stride[],
                       const ptrdiff_t imap[], double *dp);
int nc_get_varm_ushort(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const ptrdiff_t * imapp, unsigned short *ip);
int nc_get_varm_uint  (int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const ptrdiff_t * imapp, unsigned int *ip);
int nc_get_varm_longlong (int ncid, int varid, const size_t *startp, 
                          const size_t *countp, const ptrdiff_t *stridep, 
                          const ptrdiff_t * imapp, long long *ip);
int nc_get_varm_ulonglong(int ncid, int varid, const size_t *startp, 
                          const size_t *countp, const ptrdiff_t *stridep, 
                          const ptrdiff_t * imapp, unsigned long long *ip);
int nc_get_varm_string(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const ptrdiff_t * imapp, char **ip);
int nc_get_varm       (int ncid, int varid,  const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, void *ip);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID.
 
@item start
A vector of size_t integers specifying the index in the variable
where the first of the data values will be read. The indices are
relative to 0, so for example, the first data value of a variable
would have index (0, 0, ... , 0). The elements of start correspond, in
order, to the variable's dimensions. Hence, if the variable is a
record variable, the first index corresponds to the starting record
number for reading the data values.
 
@item count
A vector of size_t integers specifying the number of indices selected
along each dimension. To read a single value, for example, specify
count as (1, 1, ... , 1). The elements of count correspond, in order,
to the variable's dimensions. Hence, if the variable is a record
variable, the first element of count corresponds to a count of the
number of records to read.
 
Note: setting any element of the count array to zero causes the
function to exit without error, and without doing anything.

@item stride
A vector of ptrdiff_t integers specifying, for each dimension, the
interval between selected indices. The elements of the stride vector
correspond, in order, to the variable's dimensions. A value of 1
accesses adjacent values of the netCDF variable in the corresponding
dimension; a value of 2 accesses every other value of the netCDF
variable in the corresponding dimension; and so on. A NULL stride
argument is treated as (1, 1, ... , 1).
 
@item imap
A vector of integers that specifies the mapping between the
dimensions of a netCDF variable and the in-memory structure of the
internal data array. imap[0] gives the distance between elements of
the internal array corresponding to the most slowly varying dimension
of the netCDF variable. imap[n-1] (where n is the rank of the netCDF
variable) gives the distance between elements of the internal array
corresponding to the most rapidly varying dimension of the netCDF
variable. Intervening imap elements correspond to other dimensions of
the netCDF variable in the obvious way. Distances between elements are
specified in type-independent units of elements (the distance between
internal elements that occupy adjacent memory locations is 1 and not
the element's byte-length as in netCDF 2).
 
@item tp
@itemx up
@itemx cp
@itemx sp
@itemx ip
@itemx lp
@itemx fp
@itemx dp
Pointer to the location used for computing where the data values are
read; the data should be of the type appropriate for the function
called. If the type of data value differs from the netCDF variable
type, type conversion will occur. @xref{Type Conversion,,, netcdf, @value{n-man}}.

@end table

@heading Return Codes

@itemize

@item NC_NOERR
No error.

@item NC_EHDFERR
Error reported by HDF5 layer.

@item NC_ENOTVAR
The variable ID is invalid for the specified netCDF dataset. 

@item NC_EINVALCOORDS
The specified corner indices were out of range for the rank of the
specified variable. For example, a negative index, or an index that is
larger than the corresponding dimension length will cause an error.

@item NC_EEDGE
The specified edge lengths added to the specified corner would have
referenced data out of range for the rank of the specified
variable. For example, an edge length that is larger than the
corresponding dimension length minus the corner index will cause an
error.

@item NC_ERANGE
One or more of the specified values are out of the range of values
representable by the external data type of the variable. (Does not
apply to the nc_get_vars() function).

@item NC_EINDEFINE
The specified netCDF is in define mode rather than data mode. 

@item NC_EBADID
The specified netCDF ID does not refer to an open netCDF dataset. 

@item NC_ECHAR
Attempt to convert to or from char.

@item NC_ENOMEM
Out of memory.

@end itemize

@heading Example

The following imap vector maps in the trivial way a 4x3x2 netCDF
variable and an internal array of the same shape:

@example
float a[4][3][2];       /* same shape as netCDF variable */
size_t imap[3] = @{6, 2, 1@};
                        /* netCDF dimension       inter-element distance */
                        /* ----------------       ---------------------- */
                        /* most rapidly varying       1                  */
                        /* intermediate               2 (=imap[2]*2)     */
                        /* most slowly varying        6 (=imap[1]*3)     */
@end example

Using the imap vector above with nc_get_varm_float obtains the same
result as simply using nc_get_var_float.

Here is an example of using nc_get_varm_float to transpose a netCDF
variable named rh which is described by the C declaration float
rh[6][4] (note the size and order of the dimensions):

@example
#include <netcdf.h>
   ... 
#define NDIM 2                /* rank of netCDF variable */
int ncid;                     /* netCDF ID */
int status;                   /* error status */
int rhid;                     /* variable ID */
static size_t start[NDIM]     /* netCDF variable start point: */
                 = @{0, 0@};    /* first element */
static size_t count[NDIM]     /* size of internal array: entire netCDF */
                 = @{6, 4@};    /* variable; order corresponds to netCDF */
                              /* variable -- not internal array */
static ptrdiff_t stride[NDIM] /* variable subsampling intervals: */
                 = @{1, 1@};    /* sample every netCDF element */
static ptrdiff_t imap[NDIM]   /* internal array inter-element distances; */
                 = @{1, 6@};    /* would be @{4, 1@} if not transposing */
float rh[4][6];               /* note transposition of netCDF variable */
                              /* dimensions */
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid(ncid, "rh", &rhid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_get_varm_float(ncid, rhid, start, count, stride, imap, rh);
if (status != NC_NOERR) handle_error(status);
@end example

Here is another example of using nc_get_varm_float to simultaneously
transpose and subsample the same netCDF variable, by accessing every
other point of the netCDF variable:

@example
#include <netcdf.h>
   ... 
#define NDIM 2               /* rank of netCDF variable */
int ncid;                    /* netCDF ID */
int status;                  /* error status */
int rhid;                    /* variable ID */
static size_t start[NDIM]    /* netCDF variable start point: */
                 = @{0, 0@};   /* first element */
static size_t count[NDIM]    /* size of internal array: entire */
                   = @{3, 2@}; /* (subsampled) netCDF variable; order of */
                             /* dimensions corresponds to netCDF */
                             /* variable -- not internal array */
static ptrdiff_t stride[NDIM]/* variable subsampling intervals: */
                 = @{2, 2@};   /* sample every other netCDF element */
static ptrdiff_t imap[NDIM]  /* internal array inter-element distances; */
                 = @{1, 3@};   /* would be @{2, 1@} if not transposing */
float rh[2][3];              /* note transposition of (subsampled) */
                             /* netCDF variable dimensions */
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid(ncid, "rh", &rhid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_get_varm_float(ncid, rhid, start, count, stride, imap, rh);
if (status != NC_NOERR) handle_error(status);
@end example

@node Strings, nc_free_string, nc_get_varm_ type, Variables
@section Reading and Writing Character String Values
@cindex attributes, array of strings
@cindex string arrays

Prior to version 4.0, strings could only be stored as simple arrays of
characters. Users may still wish to store strings this way, as it
ensures maximum compatibility with other software.

Starting in netCDF-4.0, the atomic string type allows a new way to
store strings, as a variable length array in the underlying HDF5
layer. This allows arrays of strings to be stored compactly.

For more information of classic models strings @ref{Classic
Strings}. For more information on the netCDF-4.0 string type
@ref{Arrays of Strings}.

@menu
* Classic Strings::             
* Arrays of Strings::           
@end menu

@node Classic Strings, Arrays of Strings, Strings, Strings
@subsection Reading and Writing Character String Values in the Classic Model

@cindex strings in classic model
@cindex attributes, character string
@cindex byte, zero
@cindex zero byte
@cindex writing character-string data
@cindex character-string data, writing 

Character strings are not a primitive netCDF external data type, in
part because FORTRAN does not support the abstraction of
variable-length character strings (the FORTRAN LEN function returns
the static length of a character string, not its dynamic length). As a
result, a character string cannot be written or read as a single
object in the netCDF interface. Instead, a character string must be
treated as an array of characters, and array access must be used to
read and write character strings as variable data in netCDF
datasets. Furthermore, variable-length strings are not supported by
the netCDF interface except by convention; for example, you may treat
a zero byte as terminating a character string, but you must explicitly
specify the length of strings to be read from and written to netCDF
variables.

Character strings as attribute values are easier to use, since the
strings are treated as a single unit for access. However, the value of
a character-string attribute is still an array of characters with an
explicit length that must be specified when the attribute is defined.

When you define a variable that will have character-string values, use
a character-position dimension as the most quickly varying dimension
for the variable (the last dimension for the variable in C). The
length of the character-position dimension will be the maximum string
length of any value to be stored in the character-string
variable. Space for maximum-length strings will be allocated in the
disk representation of character-string variables whether you use the
space or not. If two or more variables have the same maximum length,
the same character-position dimension may be used in defining the
variable shapes.

To write a character-string value into a character-string variable,
use either entire variable access or array access. The latter requires
that you specify both a corner and a vector of edge lengths. The
character-position dimension at the corner should be zero for C. If
the length of the string to be written is n, then the vector of edge
lengths will specify n in the character-position dimension, and one
for all the other dimensions:(1, 1, ... , 1, n).

In C, fixed-length strings may be written to a netCDF dataset without
the terminating zero byte, to save space. Variable-length strings
should be written with a terminating zero byte so that the intended
length of the string can be determined when it is later read.

Here is an example that defines a record variable, tx, for character
strings and stores a character-string value into the third record
using nc_put_vara_text. In this example, we assume the string variable
and data are to be added to an existing netCDF dataset named foo.nc
that already has an unlimited record dimension time.

@example
#include <netcdf.h>
   ... 
int  ncid;            /* netCDF ID */
int  chid;            /* dimension ID for char positions */
int  timeid;          /* dimension ID for record dimension */
int  tx_id;           /* variable ID */
#define TDIMS 2       /* rank of tx variable */
int tx_dims[TDIMS];   /* variable shape */
size_t tx_start[TDIMS];
size_t tx_count[TDIMS];
static char tx_val[] =
        "example string"; /* string to be put */
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
status = nc_redef(ncid);       /* enter define mode */
if (status != NC_NOERR) handle_error(status);
   ... 
/* define character-position dimension for strings of max length 40 */
status = nc_def_dim(ncid, "chid", 40L, &chid);
if (status != NC_NOERR) handle_error(status);
   ... 
/* define a character-string variable */
tx_dims[0] = timeid;
tx_dims[1] = chid;    /* character-position dimension last */
status = nc_def_var (ncid, "tx", NC_CHAR, TDIMS, tx_dims, &tx_id);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_enddef(ncid);       /* leave define mode */
if (status != NC_NOERR) handle_error(status);
   ... 
/* write tx_val into tx netCDF variable in record 3 */
tx_start[0] = 3;      /* record number to write */
tx_start[1] = 0;      /* start at beginning of variable */
tx_count[0] = 1;      /* only write one record */
tx_count[1] = strlen(tx_val) + 1;  /* number of chars to write */
status = nc_put_vara_text(ncid, tx_id, tx_start, tx_count, tx_val);
if (status != NC_NOERR) handle_error(status);
@end example

@node Arrays of Strings,  , Classic Strings, Strings
@subsection Reading and Writing Arrays of Strings
@cindex NC_STRING, using

In netCDF-4, the NC_STRING type is introduced. It can store arrays of
strings compactly.

By using the NC_STRING type, arrays of strings (char **) can be read
and written to the file.

This allows attributes to hold more than one string. Since attributes
are one-dimensional, using the classic model, an attribute could only
hold one string, as an array of char. With the NC_STRING type, an
array of strings can be stored in one attribute.

When reading data of type NC_STRING, the HDF5 layer will allocate
memory to hold the data. It is up to the user to free this memory with
the nc_free_string function. @xref{nc_free_string}.

@example
   int ncid, varid, i, dimids[NDIMS];
   char *data[DIM_LEN] = @{"Let but your honour know",
                      "Whom I believe to be most strait in virtue", 
                      "That, in the working of your own affections", 
                      "Had time cohered with place or place with wishing", 
                      "Or that the resolute acting of your blood",
                      "Could have attain'd the effect of your own purpose",
                      "Whether you had not sometime in your life",
                      "Err'd in this point which now you censure him", 
                      "And pull'd the law upon you."@};
   char *data_in[DIM_LEN];

   printf("*** testing string attribute...");
   @{
      size_t att_len;
      int ndims, nvars, natts, unlimdimid;
      nc_type att_type;

      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
      if (nc_put_att(ncid, NC_GLOBAL, ATT_NAME, NC_STRING, DIM_LEN, data)) ERR;
      if (nc_inq(ncid, &ndims, &nvars, &natts, &unlimdimid)) ERR;
      if (ndims != 0 || nvars != 0 || natts != 1 || unlimdimid != -1) ERR;
      if (nc_inq_att(ncid, NC_GLOBAL, ATT_NAME, &att_type, &att_len)) ERR;
      if (att_type != NC_STRING || att_len != DIM_LEN) ERR;
      if (nc_close(ncid)) ERR;
      nc_exit();
      
      /* Check it out. */
      if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR;
      if (nc_inq(ncid, &ndims, &nvars, &natts, &unlimdimid)) ERR;
      if (ndims != 0 || nvars != 0 || natts != 1 || unlimdimid != -1) ERR;
      if (nc_inq_att(ncid, NC_GLOBAL, ATT_NAME, &att_type, &att_len)) ERR;
      if (att_type != NC_STRING || att_len != DIM_LEN) ERR;
      if (nc_get_att(ncid, NC_GLOBAL, ATT_NAME, data_in)) ERR; 
      for (i=0; i<att_len; i++)
         if (strcmp(data_in[i], data[i])) ERR;
      if (nc_free_string(att_len, (char **)data_in)) ERR;
      if (nc_close(ncid)) ERR;
      nc_exit();
   @}
@end example

@node nc_free_string, Fill Values, Strings, Variables
@section Releasing Memory for a NC_STRING: nc_free_string
@findex nc_free_string
@cindex NC_STRING, freeing

When a STRING is read into user memory from the file, the HDF5 library
performs memory allocations for each of the variable length character
arrays contained within the STRING structure. This memory must be
freed by the user to avoid memory leaks.

This violates the normal netCDF expectation that the user is
responsible for all memory allocation. But, with NC_STRING arrays, the
underlying HDF5 library allocates the memory for the user, and the user
is responsible for deallocating that memory.

To save the user the trouble calling free() on each element of the
NC_STRING array (i.e. the array of arrays), the nc_free_string
function is provided.

@heading Usage

@example
int nc_free_string(size_t len, char **data);
@end example

@table @code

@item len
The number of character arrays in the array.

@item **data
The pointer to the data array.

@end table

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@end table

@heading Example

@example
      if (nc_get_att(ncid, NC_GLOBAL, ATT_NAME, data_in)) ERR; 
      ...
      if (nc_free_string(att_len, (char **)data_in)) ERR;
@end example

@node Fill Values, nc_rename_var, nc_free_string, Variables
@section Fill Values
@cindex fill values
@cindex byte vs. char fill values

What happens when you try to read a value that was never written in an
open netCDF dataset? You might expect that this should always be an
error, and that you should get an error message or an error status
returned. You do get an error if you try to read data from a netCDF
dataset that is not open for reading, if the variable ID is invalid
for the specified netCDF dataset, or if the specified indices are not
properly within the range defined by the dimension lengths of the
specified variable. Otherwise, reading a value that was not written
returns a special fill value used to fill in any undefined values when
a netCDF variable is first written.

You may ignore fill values and use the entire range of a netCDF
external data type, but in this case you should make sure you write
all data values before reading them. If you know you will be writing
all the data before reading it, you can specify that no prefilling of
variables with fill values will occur by calling nc_set_fill before
writing. This may provide a significant performance gain for netCDF
writes.

The variable attribute _FillValue may be used to specify the fill
value for a variable. Their are default fill values for each type,
defined in the include file netcdf.h: NC_FILL_CHAR, NC_FILL_BYTE,
NC_FILL_SHORT, NC_FILL_INT, NC_FILL_FLOAT, and NC_FILL_DOUBLE.

The netCDF byte and character types have different default fill
values. The default fill value for characters is the zero byte, a
useful value for detecting the end of variable-length C character
strings. If you need a fill value for a byte variable, it is
recommended that you explicitly define an appropriate _FillValue
attribute, as generic utilities such as ncdump will not assume a
default fill value for byte variables.

Type conversion for fill values is identical to type conversion for
other values: attempting to convert a value from one type to another
type that can't represent the value results in a range error. Such
errors may occur on writing or reading values from a larger type (such
as double) to a smaller type (such as float), if the fill value for
the larger type cannot be represented in the smaller type.

@node nc_rename_var, nc_copy_var, Fill Values, Variables
@section Rename a Variable: nc_rename_var 
@findex nc_rename_var
@cindex nc_rename_var, example
@cindex renaming variable
@cindex variable, renaming

The function nc_rename_var changes the name of a netCDF variable in an
open netCDF dataset. If the new name is longer than the old name, the
netCDF dataset must be in define mode. You cannot rename a variable to
have the name of any existing variable.

@heading Usage 
int nc_rename_var(int ncid, int varid, const char* name);

ncid
 NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
varid
 Variable ID.
 
name
 New name for the specified variable.
 
@heading Errors 

nc_rename_var returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

The new name is in use as the name of another variable. 
The variable ID is invalid for the specified netCDF dataset. 
The specified netCDF ID does not refer to an open netCDF dataset. 

@heading Example

Here is an example using nc_rename_var to rename the variable rh to
rel_hum in an existing netCDF dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int  status;              /* error status */
int  ncid;                /* netCDF ID */
int  rh_id;               /* variable ID */
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_redef(ncid);  /* put in define mode to rename variable */
if (status != NC_NOERR) handle_error(status);
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
status = nc_rename_var (ncid, rh_id, "rel_hum");
if (status != NC_NOERR) handle_error(status);
status = nc_enddef(ncid); /* leave define mode */
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_copy_var, nc_var_par_access, nc_rename_var, Variables
@section Copy a Variable from One File to Another: nc_copy_var 
@findex nc_copy_var
@cindex variable, copying

This function will copy a variable from one file to another.

It works even if the files are different formats, (i.e. classic
vs. netCDF-4/HDF5.)

If you're copying into a netCDF-3 file, from a netCDF-4 file, you must
be copying a var of one of the six netCDF-3 types. Similarly for the
attributes.

For large netCDF-3 files, this can be a very inefficient way to copy
data from one file to another, because adding a new variable to the
target file may require more space in the header and thus result in
moving data for other variables in the target file.  This is not a problem
for netCDF-4 files, which support efficient addition of variables
without moving data for other variables.

@heading Usage 

@example
nc_copy_var(int ncid_in, int varid_in, int ncid_out)
@end example

@itemize

@item ncid_in
The file ID for the file that contains the variable to be copied.

@item varid_in
The variable ID for the variable to be copied.

@item ncid_out
The file ID for the file where the variable should be copied to.
 
@end itemize
 
@heading Return Codes

@itemize

@item NC_NOERR
No error.

@item NC_EBADID
Bad ncid.

@item NC_EBADVAR
Bad varid.

@item NC_EHDFERR
HDF5 layer error.

@item NC_ENOMEM
Out of memory.

@item NC_ERANGE
One or more values out of range.

@end itemize

@heading Example

@example
@end example

@node nc_var_par_access, nc_var_ubyte, nc_copy_var, Variables
@section Change between Collective and Independent Parallel Access: nc_var_par_access
@findex nc_var_par_access
@cindex nc_var_par_access, example

The function nc_var_par_access changes whether read/write operations
on a parallel file system are performed collectively or independently
(the default) on the variable. This function can only be called if the
file was created with nc_create_par (see @ref{nc_create_par}) or
opened with nc_open_par (see @ref{nc_open_par}).

Calling this function affects only the open file - information about
whether a variable is to be accessed collectively or independently is
not written to the data file. Every time you open a file on a parallel
file system, all variables default to independent operations. The
change a variable to collective I/O lasts only as long as that file is
open.

The variable can be changed from collective to independent, and back,
as often as desired.

Note that classic and 64-bit offset files are access using the
parallel-netcdf library, which does not allow per-variable setting of
the parallel access mode. For these files, calling nc_var_par_access
sets the access for all of the variables in the file.

@heading Usage 
int nc_var_par_access(int ncid, int varid, int access);

@table @code

@item ncid
NetCDF ID, from a previous call to nc_open_par (see @ref{nc_open_par}) or
nc_create_par (see @ref{nc_create_par}).
 
@item varid
Variable ID.
 
@item access
NC_INDEPENDENT to set this variable to independent
operations.  NC_COLLECTIVE to set it to collective operations.

@end table
 
@heading Return Values

@table @code

@item NC_NOERR
No error.

@end table

@heading Example

Here is an example using nc_var_par_access:

@example
#include <netcdf.h>

    ... 
    int ncid, v1id, dimids[NDIMS];
    int data[DIMSIZE*DIMSIZE], j, i, res;
    ...

    /* Create a parallel netcdf-4 file. */
    if ((res = nc_create_par(FILE, NC_NETCDF4|NC_MPIIO, comm, info, &ncid)))
        BAIL(res);

    /* Create two dimensions. */
    if ((res = nc_def_dim(ncid, "d1", DIMSIZE, dimids)))
       BAIL(res);
    if ((res = nc_def_dim(ncid, "d2", DIMSIZE, &dimids[1])))
       BAIL(res);

    /* Create one var. */
    if ((res = nc_def_var(ncid, "v1", NC_INT, NDIMS, dimids, &v1id)))
       BAIL(res);

    if ((res = nc_enddef(ncid)))
       BAIL(res);

    /* Tell HDF5 to use independent parallel access for this var. */
    if ((res = nc_var_par_access(ncid, v1id, NC_INDEPENDENT)))
       BAIL(res);

    /* Write slabs of phony data. */
    if ((res = nc_put_vara_int(ncid, v1id, start, count, 
                               &data[mpi_rank*QTR_DATA])))
       BAIL(res);

@end example

@node nc_var_ubyte,  , nc_var_par_access, Variables
@section Deprecated ``_ubyte'' variable functions
@findex nc_put_var1_ubyte
@findex nc_put_var_ubyte 
@findex nc_put_vara_ubyte 
@findex nc_put_vars_ubyte 
@findex nc_put_varm_ubyte 
@findex nc_get_var1_ubyte 
@findex nc_get_var_ubyte 
@findex nc_get_vara_ubyte 
@findex nc_get_vars_ubyte 
@findex nc_get_varm_ubyte 

Note: the following functions are also defined but deprecated, as they
are identical in arguments and behavior to the corresponding functions
with ``uchar'' substituted for ``ubyte'' in the function name.

@example
int nc_put_var1_ubyte (int ncid, int varid, const size_t index[],
                       const unsigned char *up);
int nc_put_var_ubyte (int ncid, int varid, const unsigned char *op);
int nc_put_vara_ubyte (int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const unsigned char *op);
int nc_put_vars_ubyte (int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const unsigned char *op);
int nc_put_varm_ubyte (int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const ptrdiff_t * imapp, const unsigned char *op);
int nc_get_var1_ubyte (int ncid, int varid, const size_t *indexp, 
                       unsigned char *ip);
int nc_get_var_ubyte (int ncid, int varid, unsigned char *ip);
int nc_get_vara_ubyte (int ncid, int varid, const size_t *startp, 
                       const size_t *countp, unsigned char *ip);
int nc_get_vars_ubyte (int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       unsigned char *ip);
int nc_get_varm_ubyte (int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const ptrdiff_t * imapp, unsigned char *ip);
@end example

@node Attributes, Summary of C Interface, Variables, Top
@chapter Attributes

@menu
* Attributes Introduction::     
* nc_put_att_ type::            
* nc_inq_att Family::           
* nc_get_att_ type::            
* nc_copy_att::                 
* nc_rename_att::               
* nc_del_att::                  
* nc_att_ubyte::                Deprecated attribute ``_ubyte'' functions
@end menu

@node Attributes Introduction, nc_put_att_ type, Attributes, Attributes
@section Introduction
@cindex attributes, introduction
@cindex attributes, operations on

Attributes may be associated with each netCDF variable to specify such
properties as units, special values, maximum and minimum valid values,
scaling factors, and offsets. Attributes for a netCDF dataset are
defined when the dataset is first created, while the netCDF dataset is
in define mode. Additional attributes may be added later by reentering
define mode. A netCDF attribute has a netCDF variable to which it is
assigned, a name, a type, a length, and a sequence of one or more
values. An attribute is designated by its variable ID and name. When
an attribute name is not known, it may be designated by its variable
ID and number in order to determine its name, using the function
nc_inq_attname.

The attributes associated with a variable are typically defined
immediately after the variable is created, while still in define
mode. The data type, length, and value of an attribute may be changed
even when in data mode, as long as the changed attribute requires no
more space than the attribute as originally defined.

It is also possible to have attributes that are not associated with
any variable. These are called global attributes and are identified by
using NC_GLOBAL as a variable pseudo-ID. Global attributes are usually
related to the netCDF dataset as a whole and may be used for purposes
such as providing a title or processing history for a netCDF dataset.

Operations supported on attributes are:
@itemize

@item
Create an attribute, given its variable ID, name, data type, length, and value. 

@item
Get attribute's data type and length from its variable ID and name. 

@item
Get attribute's value from its variable ID and name. 

@item
Copy attribute from one netCDF variable to another. 

@item
Get name of attribute from its number. 

@item
Rename an attribute. 

@item
Delete an attribute. 
@end itemize

@node nc_put_att_ type, nc_inq_att Family, Attributes Introduction, Attributes
@section Create an Attribute: nc_put_att_ @var{type}
@findex nc_put_att_ type
@cindex nc_put_att_ type, example
@cindex attributes, creating
@cindex attributes, writing
@cindex writing attributes

The function nc_put_att_ @var{type} adds or changes a variable attribute or
global attribute of an open netCDF dataset. If this attribute is new,
or if the space required to store the attribute is greater than
before, the netCDF dataset must be in define mode.

@heading Usage 

With netCDF-4 files, nc_put_att will notice if you are writing a
_Fill_Value_ attribute, and will tell the HDF5 layer to use the
specified fill value for that variable.

Although it's possible to create attributes of all types, text and
double attributes are adequate for most purposes.

Use the nc_put_att function to create attributes of any type,
including user-defined types. We recommend using the type safe versions
of this function whenever possible.

@example
int nc_put_att_text      (int ncid, int varid, const char *name, 
                          size_t len, const char *tp);
int nc_put_att_uchar     (int ncid, int varid, const char *name, nc_type xtype, 
                          size_t len, const unsigned char *up);
int nc_put_att_schar     (int ncid, int varid, const char *name, nc_type xtype,
                          size_t len, const signed char *cp);
int nc_put_att_short     (int ncid, int varid, const char *name, nc_type xtype,
                          size_t len, const short *sp);
int nc_put_att_int       (int ncid, int varid, const char *name, nc_type xtype,
                          size_t len, const int *ip);
int nc_put_att_long      (int ncid, int varid, const char *name, nc_type xtype,
                          size_t len, const long *lp);
int nc_put_att_float     (int ncid, int varid, const char *name, nc_type xtype,
                          size_t len, const float *fp);
int nc_put_att_double    (int ncid, int varid, const char *name, nc_type xtype,
                          size_t len, const double *dp);
int nc_put_att_ushort    (int ncid, int varid, const char *name, nc_type xtype,
                          size_t len, const unsigned short *op);
int nc_put_att_uint      (int ncid, int varid, const char *name, nc_type xtype,
                          size_t len, const unsigned int *op);
int nc_put_att_longlong  (int ncid, int varid, const char *name, nc_type xtype,
                          size_t len, const long long *op);
int nc_put_att_ulonglong (int ncid, int varid, const char *name, nc_type xtype,
                          size_t len, 
                          const unsigned long long *op);
int nc_put_att_string    (int ncid, int varid, const char *name, size_t len, 
                          const char **op);
int nc_put_att           (int ncid, int varid, const char *name, nc_type xtype, 
                          size_t len, const void *op);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID of the variable to which the attribute will be assigned or
NC_GLOBAL for a global attribute.
 
@item name
Attribute name.  Attribute name conventions are assumed by
some netCDF generic applications, e.g., @samp{units} as the name for a string
attribute that gives the units for a netCDF variable. For examples of
attribute conventions see @ref{Attribute Conventions,,, netcdf,
@value{n-man}}.
 
@item xtype
One of the set of predefined netCDF external data types. The type of
this parameter, nc_type, is defined in the netCDF header file. The
valid netCDF external data types are NC_BYTE, NC_CHAR, NC_SHORT,
NC_INT, NC_FLOAT, and NC_DOUBLE. Although it's possible to create
attributes of all types, NC_CHAR and NC_DOUBLE attributes are adequate
for most purposes.
 
@item len
Number of values provided for the attribute.
 
@item tp, up, cp, sp, ip, lp, fp, or dp
Pointer to one or more values. If the type of values differs from the
netCDF attribute type specified as xtype, type conversion will
occur. @xref{Type Conversion,,, netcdf, @value{n-man}}.
@end table
 
@heading Errors 

nc_put_att_ @var{type} returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The variable ID is invalid for the specified netCDF dataset. 

@item
The specified netCDF type is invalid. 

@item
The specified length is negative. 

@item
The specified open netCDF dataset is in data mode and the specified
attribute would expand.

@item
The specified open netCDF dataset is in data mode and the specified
attribute does not already exist.

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@item
The number of attributes for this variable exceeds NC_MAX_ATTRS. 

@end itemize

@heading Return Codes

@table @code

@item NC_NOERR
No error.

@item NC_EINVAL
Trying to set global _FillValue. (NetCDF-4 files only).

@item NC_ENOTVAR
Couldn't find varid.

@item NC_EBADTYPE
Fill value must be same type as variable. (NetCDF-4 files only).

@item NC_ENOMEM
Out of memory

@item NC_EFILLVALUE
Fill values must be written while the file is still in initial define
mode, that is, after the file is created, but before it leaves define
mode for the first time. NC_EFILLVALUE is returned when the user
attempts to set the fill value after it's too late.

@end table

@heading Example

Here is an example using nc_put_att_double to add a variable attribute
named valid_range for a netCDF variable named rh and a global
attribute named title to an existing netCDF dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int  status;                            /* error status */
int  ncid;                              /* netCDF ID */
int  rh_id;                             /* variable ID */
static double rh_range[] = @{0.0, 100.0@};/* attribute vals */
static char title[] = "example netCDF dataset";
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_redef(ncid);                /* enter define mode */
if (status != NC_NOERR) handle_error(status);
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_put_att_double (ncid, rh_id, "valid_range", 
                            NC_DOUBLE, 2, rh_range);
if (status != NC_NOERR) handle_error(status);
status = nc_put_att_text (ncid, NC_GLOBAL, "title",
                          strlen(title), title)
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_enddef(ncid);               /* leave define mode */
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_inq_att Family, nc_get_att_ type, nc_put_att_ type, Attributes
@section Get Information about an Attribute: nc_inq_att Family
@findex nc_inq_att Family
@cindex nc_inq_att Family, example
@cindex attributes, ID
@cindex attributes, getting information about
@cindex attributes, inquiring about
@cindex attributes, finding length
@cindex length of attributes
@cindex inquiring about attributes

This family of functions returns information about a netCDF
attribute. All but one of these functions require the variable ID and
attribute name; the exception is nc_inq_attname. Information about an
attribute includes its type, length, name, and number. See the
nc_get_att family for getting attribute values.

The function nc_inq_attname gets the name of an attribute, given its
variable ID and number. This function is useful in generic
applications that need to get the names of all the attributes
associated with a variable, since attributes are accessed by name
rather than number in all other attribute functions. The number of an
attribute is more volatile than the name, since it can change when
other attributes of the same variable are deleted. This is why an
attribute number is not called an attribute ID.

The function nc_inq_att returns the attribute's type and length. The
other functions each return just one item of information about an
attribute.


@heading Usage 
@example
int nc_inq_att    (int ncid, int varid, const char *name,
                   nc_type *xtypep, size_t *lenp);
int nc_inq_atttype(int ncid, int varid, const char *name,
                   nc_type *xtypep);
int nc_inq_attlen  (int ncid, int varid, const char *name, size_t *lenp);
int nc_inq_attname(int ncid, int varid, int attnum, char *name);
int nc_inq_attid   (int ncid, int varid, const char *name, int *attnump); 
@end example

@vtable @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID of the attribute's variable, or NC_GLOBAL for a global
attribute.
 
@item name
Attribute name. For nc_inq_attname, this is a pointer to the location
for the returned attribute name.
 
@item xtypep
Pointer to location for returned attribute type, one of the set of
predefined netCDF external data types. The type of this parameter,
nc_type, is defined in the netCDF header file. The valid netCDF
external data types are NC_BYTE, NC_CHAR, NC_SHORT, NC_INT, NC_FLOAT,
and NC_DOUBLE. If this parameter is given as '0' (a null pointer), no
type will be returned so no variable to hold the type needs to be
declared.
 
@item lenp
Pointer to location for returned number of values currently stored in
the attribute. For attributes of type NC_CHAR, you should not assume
that this includes a trailing zero byte; it doesn't if the attribute
was stored without a trailing zero byte, for example from a FORTRAN
program. Before using the value as a C string, make sure it is
null-terminated. If this parameter is given as '0' (a null pointer),
no length will be returned so no variable to hold this information
needs to be declared.
 
@item attnum
For nc_inq_attname, attribute number. The attributes for each
variable are numbered from 0 (the first attribute) to natts-1, where
natts is the number of attributes for the variable, as returned from a
call to nc_inq_varnatts.
 
@item attnump
For nc_inq_attid, pointer to location for returned attribute number
that specifies which attribute this is for this variable (or which
global attribute). If you already know the attribute name, knowing its
number is not very useful, because accessing information about an
attribute requires its name.

@end vtable

@heading Errors 

Each function returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:
@itemize

@item
The variable ID is invalid for the specified netCDF dataset. 

@item
The specified attribute does not exist. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@item
For nc_inq_attname, the specified attribute number is negative or more
than the number of attributes defined for the specified variable.
@end itemize

@heading Example

Here is an example using nc_inq_att to find out the type and length of
a variable attribute named valid_range for a netCDF variable named rh
and a global attribute named title in an existing netCDF dataset named
foo.nc:

@example
#include <netcdf.h>
   ... 
int  status;               /* error status */
int  ncid;                 /* netCDF ID */
int  rh_id;                /* variable ID */
nc_type vr_type, t_type;   /* attribute types */
size_t  vr_len, t_len;     /* attribute lengths */

   ... 
status = nc_open("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_att (ncid, rh_id, "valid_range", &vr_type, &vr_len);
if (status != NC_NOERR) handle_error(status);
status = nc_inq_att (ncid, NC_GLOBAL, "title", &t_type, &t_len);
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_get_att_ type, nc_copy_att, nc_inq_att Family, Attributes
@section Get Attribute's Values:nc_get_att_ @var{type} 
@findex nc_get_att_ type
@cindex nc_get_att_ type, example
@cindex attributes, reading
@cindex reading attributes

Members of the nc_get_att_ @var{type} family of functions get the value(s)
of a netCDF attribute, given its variable ID and name.

The nc_get_att() functions works for any type of attribute, and must
be used to get attributes of user-defined type. We recommend that they
type safe versions of this function be used where possible.

@heading Usage 
@example
int nc_get_att_text      (int ncid, int varid, const char *name, char *tp);
int nc_get_att_uchar     (int ncid, int varid, const char *name, unsigned char *up);
int nc_get_att_schar     (int ncid, int varid, const char *name, signed char *cp);
int nc_get_att_short     (int ncid, int varid, const char *name, short *sp);
int nc_get_att_int       (int ncid, int varid, const char *name, int *ip);
int nc_get_att_long      (int ncid, int varid, const char *name, long *lp);
int nc_get_att_float     (int ncid, int varid, const char *name, float *fp);
int nc_get_att_double    (int ncid, int varid, const char *name, double *dp);
int nc_get_att_ushort    (int ncid, int varid, const char *name, unsigned short *ip);
int nc_get_att_uint      (int ncid, int varid, const char *name, unsigned int *ip);
int nc_get_att_longlong  (int ncid, int varid, const char *name, long long *ip);
int nc_get_att_ulonglong (int ncid, int varid, const char *name, unsigned long long *ip);
int nc_get_att_string    (int ncid, int varid, const char *name, char **ip);
int nc_get_att           (int ncid, int varid, const char *name, void *ip);
@end example

@table @code

@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
Variable ID of the attribute's variable, or NC_GLOBAL for a global attribute.
 
@item name
Attribute name.
 
@item tp
@itemx up
@itemx cp
@itemx sp
@itemx ip
@itemx lp
@itemx fp
@itemx dp
Pointer to location for returned attribute value(s). All elements of
the vector of attribute values are returned, so you must allocate
enough space to hold them. For attributes of type NC_CHAR, you should
not assume that the returned values include a trailing zero byte; they
won't if the attribute was stored without a trailing zero byte, for
example from a FORTRAN program. Before using the value as a C string,
make sure it is null-terminated. If you don't know how much space to
reserve, call nc_inq_attlen first to find out the length of the
attribute.

@end table
 
@heading Errors 

nc_get_att_ @var{type} returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:
@itemize

@item
The variable ID is invalid for the specified netCDF dataset. 

@item
The specified attribute does not exist. 

@item
The specified netCDF ID does not refer to an open netCDF dataset. 

@item
One or more of the attribute values are out of the range of values
representable by the desired type.
@end itemize

@heading Example

Here is an example using nc_get_att_double to determine the values of
a variable attribute named valid_range for a netCDF variable named rh
and a global attribute named title in an existing netCDF dataset named
foo.nc. In this example, it is assumed that we don't know how many
values will be returned, but that we do know the types of the
attributes. Hence, to allocate enough space to store them, we must
first inquire about the length of the attributes.

@example
#include <netcdf.h>
   ... 
int  status;               /* error status */
int  ncid;                 /* netCDF ID */
int  rh_id;                /* variable ID */
int  vr_len, t_len;        /* attribute lengths */
double *vr_val;            /* ptr to attribute values */
char *title;               /* ptr to attribute values */
extern char *malloc();     /* memory allocator */

   ... 
status = nc_open("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
/* find out how much space is needed for attribute values */
status = nc_inq_attlen (ncid, rh_id, "valid_range", &vr_len);
if (status != NC_NOERR) handle_error(status);
status = nc_inq_attlen (ncid, NC_GLOBAL, "title", &t_len);
if (status != NC_NOERR) handle_error(status);

/* allocate required space before retrieving values */
vr_val = (double *) malloc(vr_len * sizeof(double));
title = (char *) malloc(t_len + 1);  /* + 1 for trailing null */

/* get attribute values */
status = nc_get_att_double(ncid, rh_id, "valid_range", vr_val);
if (status != NC_NOERR) handle_error(status);
status = nc_get_att_text(ncid, NC_GLOBAL, "title", title);
if (status != NC_NOERR) handle_error(status);
title[t_len] = '\0';       /* null terminate */
   ... 
@end example

@node nc_copy_att, nc_rename_att, nc_get_att_ type, Attributes
@section Copy Attribute from One NetCDF to Another: nc_copy_att 
@findex nc_copy_att
@cindex nc_copy_att, example
@cindex attributes, copying
@cindex copying attributes

The function nc_copy_att copies an attribute from one open netCDF
dataset to another. It can also be used to copy an attribute from one
variable to another within the same netCDF.

If used to copy an attribute of user-defined type, then that
user-defined type must already be defined in the target file. In the
case of user-defined attributes, enddef/redef is called for 
ncid_in and ncid_out if they are in define mode. (This is the ensure
that all user-defined types are committed to the file(s) before the
copy is attempted.)

@heading Usage 
@example
int nc_copy_att (int ncid_in, int varid_in, const char *name,
                 int ncid_out, int varid_out);
@end example

@table @code
@item ncid_in
The netCDF ID of an input netCDF dataset from which the attribute
will be copied, from a previous call to nc_open or nc_create.
 
@item varid_in
ID of the variable in the input netCDF dataset from which the
attribute will be copied, or NC_GLOBAL for a global attribute.
 
@item name
Name of the attribute in the input netCDF dataset to be copied.
 
@item ncid_out
The netCDF ID of the output netCDF dataset to which the attribute
will be copied, from a previous call to nc_open or nc_create. It is
permissible for the input and output netCDF IDs to be the same. The
output netCDF dataset should be in define mode if the attribute to be
copied does not already exist for the target variable, or if it would
cause an existing target attribute to grow.
 
@item varid_out
ID of the variable in the output netCDF dataset to which the
attribute will be copied, or NC_GLOBAL to copy to a global attribute.
@end table
 
@heading Errors 

nc_copy_att returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The input or output variable ID is invalid for the specified netCDF
dataset.

@item
The specified attribute does not exist. 

@item
The output netCDF is not in define mode and the attribute is new for
the output dataset is larger than the existing attribute.

@item
The input or output netCDF ID does not refer to an open netCDF
dataset.
@end itemize

@heading Example

Here is an example using nc_copy_att to copy the variable attribute
units from the variable rh in an existing netCDF dataset named foo.nc
to the variable avgrh in another existing netCDF dataset named bar.nc,
assuming that the variable avgrh already exists, but does not yet have
a units attribute:

@example
#include <netcdf.h>
   ... 
int  status;               /* error status */
int  ncid1, ncid2;         /* netCDF IDs */
int  rh_id, avgrh_id;      /* variable IDs */
   ... 
status = nc_open("foo.nc", NC_NOWRITE, ncid1);
if (status != NC_NOERR) handle_error(status);
status = nc_open("bar.nc", NC_WRITE, ncid2);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid1, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
status = nc_inq_varid (ncid2, "avgrh", &avgrh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_redef(ncid2);  /* enter define mode */
if (status != NC_NOERR) handle_error(status);
/* copy variable attribute from "rh" to "avgrh" */
status = nc_copy_att(ncid1, rh_id, "units", ncid2, avgrh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_enddef(ncid2); /* leave define mode */
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_rename_att, nc_del_att, nc_copy_att, Attributes
@section Rename an Attribute: nc_rename_att 
@findex nc_rename_att
@cindex nc_rename_att, example
@cindex attributes, renaming
@cindex renaming attributes

The function nc_rename_att changes the name of an attribute. If the
new name is longer than the original name, the netCDF dataset must be
in define mode. You cannot rename an attribute to have the same name
as another attribute of the same variable.

@heading Usage 
@example
int nc_rename_att (int ncid, int varid, const char* name, 
                   const char* newname);
@end example

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
ID of the attribute's variable, or NC_GLOBAL for a global attribute
 
@item name
The current attribute name.
 
@item newname
The new name to be assigned to the specified attribute. If the new
name is longer than the current name, the netCDF dataset must be in
define mode.
@end table
 
@heading Errors 

nc_rename_att returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:
@itemize

@item
The specified variable ID is not valid. 

@item
The new attribute name is already in use for another attribute of the
specified variable.

@item
The specified netCDF dataset is in data mode and the new name is
longer than the old name.

@item
The specified attribute does not exist. 

@item
The specified netCDF ID does not refer to an open netCDF dataset.
@end itemize

@heading Example

Here is an example using nc_rename_att to rename the variable
attribute units to Units for a variable rh in an existing netCDF
dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int  status;      /* error status */
int  ncid;        /* netCDF ID */
int  rh_id;       /* variable id */
   ... 
status = nc_open("foo.nc", NC_NOWRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
/* rename attribute */
status = nc_rename_att(ncid, rh_id, "units", "Units");
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_del_att, nc_att_ubyte, nc_rename_att, Attributes
@section Delete an Attribute: nc_del_att 
@findex nc_del_att
@cindex nc_del_att, example
@cindex attributes, deleting
@cindex deleting attributes

The function nc_del_att deletes a netCDF attribute from an open netCDF
dataset. The netCDF dataset must be in define mode.

@heading Usage 
int nc_del_att (int ncid, int varid, const char* name);

@table @code
@item ncid
NetCDF or group ID, from a previous call to nc_open, nc_create,
nc_def_grp, or associated inquiry functions such as nc_inq_ncid.
 
@item varid
ID of the attribute's variable, or NC_GLOBAL for a global attribute.
 
@item name
The name of the attribute to be deleted.
@end table
 
@heading Errors 

nc_del_att returns the value NC_NOERR if no errors
occurred. Otherwise, the returned status indicates an error. Possible
causes of errors include:

@itemize

@item
The specified variable ID is not valid. 

@item
The specified netCDF dataset is in data mode. 

@item
The specified attribute does not exist. 

@item
The specified netCDF ID does not refer to an open netCDF dataset.
@end itemize

@heading Example

Here is an example using nc_del_att to delete the variable attribute
Units for a variable rh in an existing netCDF dataset named foo.nc:

@example
#include <netcdf.h>
   ... 
int  status;      /* error status */
int  ncid;        /* netCDF ID */
int  rh_id;       /* variable ID */
   ... 
status = nc_open("foo.nc", NC_WRITE, &ncid);
if (status != NC_NOERR) handle_error(status);
   ... 
status = nc_inq_varid (ncid, "rh", &rh_id);
if (status != NC_NOERR) handle_error(status);
   ... 
/* delete attribute */
status = nc_redef(ncid);        /* enter define mode */
if (status != NC_NOERR) handle_error(status);
status = nc_del_att(ncid, rh_id, "Units");
if (status != NC_NOERR) handle_error(status);
status = nc_enddef(ncid);       /* leave define mode */
if (status != NC_NOERR) handle_error(status);
@end example

@node nc_att_ubyte, , nc_del_att, Attributes
@findex nc_put_att_ubyte
@findex nc_get_att_ubyte

Note: the following functions are also defined but deprecated, as they
are identical in arguments and behavior to the corresponding functions
with ``uchar'' substituted for ``ubyte'' in the function name.

@example
int nc_put_att_ubyte     (int ncid, int varid, const char *name, nc_type xtype,
                          size_t len, const unsigned char *op);
int nc_get_att_ubyte     (int ncid, int varid, const char *name, unsigned char *ip);
@end example


@node Summary of C Interface, NetCDF 3 Transition Guide, Attributes, Top
@appendix Summary of C Interface
@cindex API, C summary
@cindex C API summary

@example
const char* nc_inq_libvers (void);
const char* nc_strerror    (int ncerr);

int nc_create         (const char *path, int cmode, int *ncidp);
int nc_open           (const char *path, int mode, int *ncidp);
int nc_set_fill       (int ncid, int fillmode, int *old_modep);
int nc_redef          (int ncid);
int nc_enddef         (int ncid);
int nc_sync           (int ncid);
int nc_abort          (int ncid);
int nc_close          (int ncid);
int nc_inq            (int ncid, int *ndimsp, int *nvarsp,
                       int *ngattsp, int *unlimdimidp);
int nc_inq_ndims      (int ncid, int *ndimsp);
int nc_inq_nvars      (int ncid, int *nvarsp);
int nc_inq_natts      (int ncid, int *ngattsp);
int nc_inq_unlimdim   (int ncid, int *unlimdimidp);

int nc_def_dim        (int ncid, const char *name, size_t len,
                       int *idp);
int nc_inq_dimid      (int ncid, const char *name, int *idp);
int nc_inq_dim        (int ncid, int dimid, char *name, size_t *lenp);
int nc_inq_dimname    (int ncid, int dimid, char *name);
int nc_inq_dimlen     (int ncid, int dimid, size_t *lenp);
int nc_rename_dim     (int ncid, int dimid, const char *name);

int nc_def_var        (int ncid, const char *name, nc_type xtype,
                       int ndims, const int *dimidsp, int *varidp);
int nc_inq_var        (int ncid, int varid, char *name, 
                       nc_type *xtypep, int *ndimsp, int *dimidsp,
                       int *nattsp);
int nc_inq_varid      (int ncid, const char *name, int *varidp);
int nc_inq_varname    (int ncid, int varid, char *name);
int nc_inq_vartype    (int ncid, int varid, nc_type *xtypep);
int nc_inq_varndims   (int ncid, int varid, int *ndimsp);
int nc_inq_vardimid   (int ncid, int varid, int *dimidsp);
int nc_inq_varnatts   (int ncid, int varid, int *nattsp);
int nc_rename_var     (int ncid, int varid, const char *name);
int nc_put_var_text   (int ncid, int varid, const char *op);
int nc_get_var_text   (int ncid, int varid,       char *ip);
int nc_put_var_uchar  (int ncid, int varid, const unsigned char *op);
int nc_get_var_uchar  (int ncid, int varid,       unsigned char *ip);
int nc_put_var_schar  (int ncid, int varid, const signed char *op);
int nc_get_var_schar  (int ncid, int varid,       signed char *ip);
int nc_put_var_short  (int ncid, int varid, const short *op);
int nc_get_var_short  (int ncid, int varid,       short *ip);
int nc_put_var_int    (int ncid, int varid, const int *op);
int nc_get_var_int    (int ncid, int varid,       int *ip);
int nc_put_var_long   (int ncid, int varid, const long *op);
int nc_get_var_long   (int ncid, int varid,       long *ip);
int nc_put_var_float  (int ncid, int varid, const float *op); 
int nc_get_var_float  (int ncid, int varid,       float *ip); 
int nc_put_var_double (int ncid, int varid, const double *op);
int nc_get_var_double (int ncid, int varid,       double *ip);
int nc_put_var1_text  (int ncid, int varid, const size_t *indexp,
                       const char *op);
int nc_get_var1_text  (int ncid, int varid, const size_t *indexp,
                       char *ip);
int nc_put_var1_uchar (int ncid, int varid, const size_t *indexp,
                       const unsigned char *op);
int nc_get_var1_uchar (int ncid, int varid, const size_t *indexp,
                       unsigned char *ip);
int nc_put_var1_schar (int ncid, int varid, const size_t *indexp,
                       const signed char *op);
int nc_get_var1_schar (int ncid, int varid, const size_t *indexp,
                       signed char *ip);
int nc_put_var1_short (int ncid, int varid, const size_t *indexp,
                       const short *op);
int nc_get_var1_short (int ncid, int varid, const size_t *indexp,
                       short *ip);
int nc_put_var1_int   (int ncid, int varid, const size_t *indexp,
                       const int *op);
int nc_get_var1_int   (int ncid, int varid, const size_t *indexp,
                       int *ip);
int nc_put_var1_long  (int ncid, int varid, const size_t *indexp,
                       const long *op);
int nc_get_var1_long  (int ncid, int varid, const size_t *indexp,
                       long *ip);
int nc_put_var1_float (int ncid, int varid, const size_t *indexp,
                       const float *op); 
int nc_get_var1_float (int ncid, int varid, const size_t *indexp,
                       float *ip); 
int nc_put_var1_double(int ncid, int varid, const size_t *indexp,
                       const double *op);
int nc_get_var1_double(int ncid, int varid, const size_t *indexp,
                       double *ip);
int nc_put_vara_text  (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const char *op);
int nc_get_vara_text  (int ncid, int varid, const size_t *startp,
                       const size_t *countp, char *ip);
int nc_put_vara_uchar (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const unsigned char *op);
int nc_get_vara_uchar (int ncid, int varid, const size_t *startp,
                       const size_t *countp, unsigned char *ip);
int nc_put_vara_schar (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const signed char *op);
int nc_get_vara_schar (int ncid, int varid, const size_t *startp,
                       const size_t *countp, signed char *ip);
int nc_put_vara_short (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const short *op);
int nc_get_vara_short (int ncid, int varid, const size_t *startp,
                       const size_t *countp, short *ip);
int nc_put_vara_int   (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const int *op);
int nc_get_vara_int   (int ncid, int varid, const size_t *startp,
                       const size_t *countp, int *ip);
int nc_put_vara_long  (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const long *op);
int nc_get_vara_long  (int ncid, int varid, const size_t *startp,
                       const size_t *countp, long *ip);
int nc_put_vara_float (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const float *op);
int nc_get_vara_float (int ncid, int varid, const size_t *startp,
                       const size_t *countp, float *ip);
int nc_put_vara_double(int ncid, int varid, const size_t *startp,
                       const size_t *countp, const double *op);
int nc_get_vara_double(int ncid, int varid, const size_t *startp,
                       const size_t *countp, double *ip);
int nc_put_vars_text  (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const char *op);
int nc_get_vars_text  (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       char *ip);
int nc_put_vars_uchar (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const unsigned char *op);
int nc_get_vars_uchar (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       unsigned char *ip);
int nc_put_vars_schar (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const signed char *op);
int nc_get_vars_schar (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       signed char *ip);
int nc_put_vars_short (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const short *op);
int nc_get_vars_short (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       short *ip);
int nc_put_vars_int   (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const int *op);
int nc_get_vars_int   (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       int *ip);
int nc_put_vars_long  (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const long *op);
int nc_get_vars_long  (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       long *ip);
int nc_put_vars_float (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const float *op);
int nc_get_vars_float (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       float *ip);
int nc_put_vars_double(int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const double *op);
int nc_get_vars_double(int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       double *ip);
int nc_put_varm_text  (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, const char *op);
int nc_get_varm_text  (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, char *ip);
int nc_put_varm_uchar (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, const unsigned char *op);
int nc_get_varm_uchar (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, unsigned char *ip);
int nc_put_varm_schar (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, const signed char *op);
int nc_get_varm_schar (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, signed char *ip);
int nc_put_varm_short (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, const short *op);
int nc_get_varm_short (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, short *ip);
int nc_put_varm_int   (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, const int *op);
int nc_get_varm_int   (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, int *ip);
int nc_put_varm_long  (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, const long *op);
int nc_get_varm_long  (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, long *ip);
int nc_put_varm_float (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, const float *op);
int nc_get_varm_float (int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, float *ip);
int nc_put_varm_double(int ncid, int varid, const size_t *startp,
                       const size_t *countp, const ptrdiff_t *stridep,
                       const ptrdiff_t *imapp, const double *op);  
int nc_get_varm_double(int ncid, int varid, const size_t *startp, 
                       const size_t *countp, const ptrdiff_t *stridep, 
                       const ptrdiff_t * imap, double *ip);

int nc_inq_att        (int ncid, int varid, const char *name,
                       nc_type *xtypep, size_t *lenp);
int nc_inq_attid      (int ncid, int varid, const char *name, int *idp);
int nc_inq_atttype    (int ncid, int varid, const char *name,
                       nc_type *xtypep);
int nc_inq_attlen     (int ncid, int varid, const char *name,
                       size_t *lenp);
int nc_inq_attname    (int ncid, int varid, int attnum, char *name);
int nc_copy_att       (int ncid_in, int varid_in, const char *name,
                       int ncid_out, int varid_out);
int nc_rename_att     (int ncid, int varid, const char *name,
                       const char *newname);
int nc_del_att        (int ncid, int varid, const char *name);
int nc_put_att_text   (int ncid, int varid, const char *name, size_t len,
                       const char *op);
int nc_get_att_text   (int ncid, int varid, const char *name, char *ip);
int nc_put_att_uchar  (int ncid, int varid, const char *name,
                       nc_type xtype, size_t len, const unsigned char *op);
int nc_get_att_uchar  (int ncid, int varid, const char *name,
                       unsigned char *ip);
int nc_put_att_schar  (int ncid, int varid, const char *name,
                       nc_type xtype, size_t len, const signed char *op);
int nc_get_att_schar  (int ncid, int varid, const char *name,
                       signed char *ip);
int nc_put_att_short  (int ncid, int varid, const char *name,
                       nc_type xtype, size_t len, const short *op);
int nc_get_att_short  (int ncid, int varid, const char *name, short *ip);
int nc_put_att_int    (int ncid, int varid, const char *name,
                       nc_type xtype,size_t len, const int *op);
int nc_get_att_int    (int ncid, int varid, const char *name, int *ip);
int nc_put_att_long   (int ncid, int varid, const char *name,
                       nc_type xtype, size_t len, const long *op);
int nc_get_att_long   (int ncid, int varid, const char *name, long *ip);
int nc_put_att_float  (int ncid, int varid, const char *name,
                        nc_type xtype, size_t len, const float *op);
int nc_get_att_float  (int ncid, int varid, const char *name, float *ip);
int nc_put_att_double (int ncid, int varid, const char *name,
                       nc_type xtype, size_t len, const double *op);
int nc_get_att_double (int ncid, int varid, const char *name, 
                       double *ip);
@end example

@node NetCDF 3 Transition Guide, NetCDF 2 C Transition Guide, Summary of C Interface, Top
@appendix NetCDF 3 to NetCDF 4 Transition Guide

@section Introduction

The release of netCDF-4 represents a substantial increase in the
capabilities of the netCDF C and Fortran APIs.

The netCDF-4.0 release (June, 2008) allows the use of the popular HDF5
data format as a storage layer. The HDF5 format has many features, and
only a subset of them are exposed in the netCDF-4 API. This represents
a deliberate selection process by netCDF-4 developers to
choose the most useful features of the HDF5 model, while retaining the
simplicity of the netCDF APIs.

Despite many new features, full backward compatibility is assured (and
extensively tested). Existing software and data files will continue to
work with netCDF-4.0, just as with previous releases of the netCDF
library.

The use of netCDF-4 files allows the use of the expanded data model,
including user-defined types, groups, the new unsigned, 64-bit, and
string types.

Using netCDF-4 files also allows the use of such features as endianness
control, per-variable data compression, chunking, parallel I/O, and
checksums. These features fit neatly within the classic netCDF data
model. 

Although the expanded data model offers many exciting new features, we
expect and encourage users to proceed with care - it also allows the
creation of needlessly, even horribly complex files. This would
decrease interoperability and increase the work of the poor
programmers trying to use the data file. 

There are many netCDF-4 features which fit comfortably within the
classic netCDF model. Existing programs can be very quickly converted
to use features such as compression, endianness control, and
chunking. This allows users to gain immediate performance pay off,
with minimal software development effort.

@section NetCDF-4 and HDF5

NetCDF-4 depends on HDF5 to deliver the new features of the expanded
data model, as well as the features required to support the classic
data model.

NetCDF-4 users must have at least HDF5 version 1.8.1 (and at least
zlib-1.2.3) to use HDF5 with netCDF-4.0. If these packages are not
found when netCDF is built, then the netCDF library may still be built
(without the --enable-netcdf-4 option), but will not allow users to
create netCDF-4/HDF5 files, or use the expanded data model. Only
classic and 64-bit offset format netCDF files will be created or
readable. (@pxref{Configure,,, netcdf-install, @value{i-man}}).

The HDF5 files created by netCDF-4 will be readable (and writable) by
any HDF5 application. However, netCDF-4.0 cannot read any HDF5 file,
only those created by netCDF-4.

@section Backward Compatibility

In the context of netCDF, backward compatibility has several
meanings. 

@table @code

@item Data Compatibility
NetCDF-4 provides backward compatibility for existing data. All netCDF
data files remain readable and writable to the netCDF library. When a file is
opened, the library detects the underlying format of the file; this is
transparent to the programmer and user.

@item Code Compatibility
NetCDF-4 provides backward compatibility for existing
software. Programs using the 4.0 release can use it as a drop-in
replacement for netCDF-3.x. Existing programs will continue to create
netCDF classic or 64-bit offset files.

@item Model Compatibility
NetCDF-4 introduces an expanded model of a netCDF data file
(include such new elements as groups, user-defined types,
multiple-unlimited dimensions, etc.) This expanded model is a super-set
of the classic netCDF model. Everything that works in the classic
model works in the expanded model as well. (The reverse is not true -
code using the expanded data model will fail if run on classic model
netCDF files.)

@end table

@section  The Classic and the Expanded NetCDF Data Models

The classic netCDF data model consists of variables, dimensions, and
attributes. 

The netCDF-4.0 release introduces an expanded data model, which offers
many new features. These features will only work on files which have
been created with the NC_NETCDF4 flag, and without the
NC_CLASSIC_MODEL flag (@pxref{nc_create}).

@table @code

@item New Types
New data types are introduced: NC_UBYTE, NC_USHORT, NC_UINT, NC_INT64,
NC_UINT64, and NC_STRING. These types many be used for attributes and
variables. @xref{nc_def_var}.

@item Groups
NetCDF objects may now be organizes into a hierarchical set of
groups. Groups are organized much line a UNIX file system, with each
group capable of containing more groups.  Within each group a
classic model netCDF ``file'' exists, with its own dimensions,
variables, and attributes. @xref{nc_def_grp}.

@item User Defined Types
NetCDF-4 allows the user to define new data types, including a
compound type (@pxref{nc_def_compound}), a variable length array type
(@pxref{nc_def_vlen}), an enumerated type (@pxref{nc_def_enum}), and
an opaque type (@pxref{nc_def_opaque}).

@item Multiple Unlimited Dimensions
NetCDF-4/HDF5 data files may use multiple unlimited dimensions with a
file, and even within a variable. 

@end table

@section Using NetCDF-4.0 with the Classic and 64-bit Offset Formats

Prior to the 4.0 release, two underlying data formats were available
for the netCDF user, the classic, and the 64-bit offset format. (The
64-bit offset format was introduced in the 3.6.0 release, and allows
the use of larger variables and files).

Software using netCDF, relinked against the netCDF-4.0 library, will
continue to work exactly as before. Since the default create mode in
nc_create is to create a classic format file, using unmodified
netCDF-3 code with the netCDF-4 library will result in the exact same
output - a classic netCDF file or 64-bit offset file.

When writing or reading classic and 64-bit offset files, the
netCDF-4.0 library relies on the core netCDF-3.x code. 

@section Creating a NetCDF-4/HDF5 File

The extra features of netCDF-4 can only be accessed by adding the
NC_NETCDF4 flag to the create mode of nc_create. Files created with the
NC_NETCDF4 flag can have multiple unlimited dimensions, use the new
atomic types, use compound and opaque types, and take advantage of the
other features of netCDF-4. (@pxref{nc_create}).

@section Using NetCDF-4.0 with the Classic Model

By changing your nc_create call to create a netCDF-4/HDF5 file you
gain access to many new features - perhaps too many! Using groups or
user-defined types will make the file unreadable to existing netCDF
applications, until they are updated to handle the new netCDF-4 model.

Using the NC_CLASSIC_MODEL flag with the NC_NETCDF4 flag tells the
library to create a netCDF-4/HDF5 file which must abide by the rules
of the classic netCDF data model. Such a file many not contain groups,
user defined types, multiple unlimited dimensions, etc.

But a classic model file is guaranteed to be compatible with existing
netCDF software, once relinked to the netCDF 4.0 library. 

Some features of netCDF-4 are transparent to the user when the file is
read. For example, a netCDF-4/HDF5 file may contain compressed
data. When such a file is read, the decompression of the data takes
place transparently. This means that data may use the data compression
feature, and still conform to the classic netCDF data model, and thus
retain compatibility with existing netCDF software
(@pxref{nc_def_var_deflate}). The same applies for control of
endianness (@pxref{nc_def_var_endian}), chunking
(@pxref{nc_def_var_chunking}), checksums
(@pxref{nc_def_var_fletcher32}), and parallel I/O, if netCDF-4 was
built on a system with the MPI libraries.

To use these feature, change your nc_create calls to use the
NC_NETCDF4 and NC_CLASSIC_MODEL flags. Then call the appropriate
nc_dev_var_* function after the variable is defined, but before the
next call to nc_enddef.

@section Use of the Expanded Model Impacts Fortran Portability

Using expanded model features impacts portability for Fortran
programmers.

Fortran compilers do not always agree as to how data should be laid
out in memory. This makes handling compound and variable length array
types compiler and platform dependant.

(This is also true for C, but the clever HDF5 configuration has solved
this problem for C. Alas, not for Fortran.) 

Despite this, Fortran programs can take advantage of the new data
model. The portability challenge is no different from that which
Fortran programmers already deal with when doing data I/O.

@section The C++ API Does Not Handle Expanded Model in this Release

Unfortunately, the C++ API does not support the netCDF-4 expanded data
model. A new C++ API is being developed and may be built by
adventurous users using the --enable-cxx4 option to configure
(@pxref{Configure,,, netcdf-install, @value{i-man}}).

@node NetCDF 2 C Transition Guide, NetCDF-3 Error Codes, NetCDF 3 Transition Guide, Top
@appendix NetCDF 2 to NetCDF 3 C Transition Guide
@cindex backward compatibility with v2 API
@cindex zero length edge
@cindex zero valued count vector
@cindex XDR library
@cindex netCDF 2 transition guide
@cindex transition guide, netCDF 2

@section Overview of C interface changes

NetCDF version 3 includes a complete rewrite of the netCDF library. It
is about twice as fast as the previous version. The netCDF file format
is unchanged, so files written with version 3 can be read with version
2 code and vice versa.

The core library is now written in ANSI C. For example, prototypes are
used throughout as well as const qualifiers where appropriate. You
must have an ANSI C compiler to compile this version.

Rewriting the library offered an opportunity to implement improved C
and FORTRAN interfaces that provide some significant benefits:

type safety, by eliminating the need to use generic void* pointers;

automatic type conversions, by eliminating the undesirable coupling
between the language-independent external netCDF types (NC_BYTE, ...,
NC_DOUBLE) and language-dependent internal data types (char, ...,
double);

support for future enhancements, by eliminating obstacles to the clean
addition of support for packed data and multithreading;

more standard error behavior, by uniformly communicating an error
status back to the calling program in the return value of each
function.

It is not necessary to rewrite programs that use the version 2 C
interface, because the netCDF-3 library includes a backward
compatibility interface that supports all the old functions, globals,
and behavior. We are hoping that the benefits of the new interface
will be an incentive to use it in new netCDF applications. It is
possible to convert old applications to the new interface
incrementally, replacing netCDF-2 calls with the corresponding
netCDF-3 calls one at a time. If you want to check that only netCDF-3
calls are used in an application, a preprocessor macro (NO_NETCDF_2)
is available for that purpose.

Other changes in the implementation of netCDF result in improved
portability, maintainability, and performance on most platforms. A
clean separation between I/O and type layers facilitates
platform-specific optimizations. The new library no longer uses a
vendor-provided XDR library, which simplifies linking programs that
use netCDF and speeds up data access significantly in most cases.

@section The New C Interface

First, here's an example of C code that uses the netCDF-2 interface:

@example
void *bufferp;
nc_type xtype;
ncvarinq(ncid, varid, ..., &xtype, ...
...
/* allocate bufferp based on dimensions and type */
...
if (ncvarget(ncid, varid, start, count, bufferp) == -1) @{
    fprintf(stderr, "Can't get data, error code = %d\n",ncerr);
    /* deal with it */
    ...
@}
switch(xtype) @{
    /* deal with the data, according to type */
...
case  NC_FLOAT:
    fanalyze((float *)bufferp);
    break;
case NC_DOUBLE:
    danalyze((double *)bufferp);
    break;
@}
@end example

Here's how you might handle this with the new netCDF-3 C interface:

@example
/*
 * I want to use doubles for my analysis.
 */
double dbuf[NDOUBLES];
int status;

/* So, I use the function that gets the data as doubles. */
status = nc_get_vara_double(ncid, varid, start, count, dbuf)
if (status != NC_NOERR) @{
   fprintf(stderr, "Can't get data: %s\n", nc_strerror(status));
    /* deal with it */
    ...
@}
danalyze(dbuf);
@end example

The example above illustrates changes in function names, data type
conversion, and error handling, discussed in detail in the sections
below.

@section Function Naming Conventions

The netCDF-3 C library employs a new naming convention, intended to
make netCDF programs more readable. For example, the name of the
function to rename a variable is now nc_rename_var instead of the
previous ncvarrename.

All netCDF-3 C function names begin with the nc_ prefix. The second
part of the name is a verb, like get, put, inq (for inquire), or
open. The third part of the name is typically the object of the verb:
for example dim, var, or att for functions dealing with dimensions,
variables, or attributes. To distinguish the various I/O operations
for variables, a single character modifier is appended to var:

@table @asis
@item var
entire variable access 

@item var1
single value access 

@item vara
array or array section access 

@item vars
strided access to a subsample of values 

@item varm
mapped access to values not contiguous in memory 

@end table

At the end of the name for variable and attribute functions, there is
a component indicating the type of the final argument: text, uchar,
schar, short, int, long, float, or double. This part of the function
name indicates the type of the data container you are using in your
program: character string, unsigned char, signed char, and so on.

Also, all macro names in the public C interface begin with the prefix
NC_. For example, the macro which was formerly MAX_NC_NAME is now
NC_MAX_NAME, and the former FILL_FLOAT is now NC_FILL_FLOAT.

As previously mentioned, all the old names are still supported for
backward compatibility.

@section Type Conversion

With the new interface, users need not be aware of the external type
of numeric variables, since automatic conversion to or from any
desired numeric type is now available. You can use this feature to
simplify code, by making it independent of external types. The
elimination of void* pointers provides detection of type errors at
compile time that could not be detected with the previous
interface. Programs may be made more robust with the new interface,
because they need not be changed to accommodate a change to the
external type of a variable.

If conversion to or from an external numeric type is necessary, it is
handled by the library. This automatic conversion and separation of
external data representation from internal data types will become even
more important in netCDF version 4, when new external types will be
added for packed data for which there is no natural corresponding
internal type, for example, arrays of 11-bit values.

Converting from one numeric type to another may result in an error if
the target type is not capable of representing the converted
value. (In netCDF-2, such overflows can only happen in the XDR layer.)
For example, a float may not be able to hold data stored externally as
an NC_DOUBLE (an IEEE floating-point number). When accessing an array
of values, an NC_ERANGE error is returned if one or more values are
out of the range of representable values, but other values are
converted properly.

Note that mere loss of precision in type conversion does not return an
error. Thus, if you read double precision values into an int, for
example, no error results unless the magnitude of the double precision
value exceeds the representable range of ints on your
platform. Similarly, if you read a large integer into a float
incapable of representing all the bits of the integer in its mantissa,
this loss of precision will not result in an error. If you want to
avoid such precision loss, check the external types of the variables
you access to make sure you use an internal type that has a compatible
precision.

The new interface distinguishes arrays of characters intended to
represent text strings from arrays of 8-bit bytes intended to
represent small integers. The interface supports the internal types
text, uchar, and schar, intended for text strings, unsigned byte
values, and signed byte values.

The _uchar and _schar functions were introduced in netCDF-3 to
eliminate an ambiguity, and support both signed and unsigned byte
data. In netCDF-2, whether the external NC_BYTE type represented
signed or unsigned values was left up to the user. In netcdf-3, we
treat NC_BYTE as signed for the purposes of conversion to short, int,
long, float, or double. (Of course, no conversion takes place when the
internal type is signed char.) In the _uchar functions, we treat
NC_BYTE as if it were unsigned. Thus, no NC_ERANGE error can occur
converting between NC_BYTE and unsigned char.  The _uchar and _schar
functions will behave differently when writing data or attribute
values to a larger type, because the type conversion is from unsigned
or signed to the larger type, respectively.

@section Error handling

The new interface handles errors differently than netCDF-2. In the old
interface, the default behavior when an error was detected was to
print an error message and exit. To get control of error handling, you
had to set flag bits in a global variable, ncopts, and to determine
the cause of an error, you had to test the value of another global
variable ncerr.

In the new interface, functions return an integer status that
indicates not only success or failure, but also the cause of the
error. The global variables ncerr and ncopt have been eliminated. The
library will never try to print anything, nor will it call exit
(unless you are using the netCDF version 2 compatibility
functions). You will have to check the function return status and do
this yourself. We eliminated these globals in the interest of
supporting parallel (multiprocessor) execution cleanly, as well as
reducing the number of assumptions about the environment where netCDF
is used. The new behavior should provide better support for using
netCDF as a hidden layer in applications that have their own GUI
interface.

@section NC_LONG and NC_INT 

Where the netCDF-2 interface used NC_LONG to
identify an external data type corresponding to 32-bit integers, the
new interface uses NC_INT instead. NC_LONG is defined to have the same
value as NC_INT for backward compatibility, but it should not be used
in new code. With new 64-bit platforms using long for 64-bit integers,
we would like to reduce the confusion caused by this name clash. Note
that there is still no netCDF external data type corresponding to
64-bit integers.

@section What's Missing?  

The new C interface omits three "record I/O" functions, ncrecput,
ncrecget, and ncrecinq, from the netCDF-2 interface, although these
functions are still supported via the netCDF-2 compatibility
interface.

This means you may have to replace one record-oriented call with
multiple type-specific calls, one for each record variable. For
example, a single call to ncrecput can always be replaced by multiple
calls to the appropriate nc_put_var functions, one call for each
variable accessed. The record-oriented functions were omitted, because
there is no simple way to provide type-safety and automatic type
conversion for such an interface.

There is no function corresponding to the nctypelen function from the
version 2 interface. The separation of internal and external types and
the new type-conversion interfaces make nctypelen unnecessary. Since
users read into and write out of native types, the sizeof operator is
perfectly adequate to determine how much space to allocate for a
value.

In the previous library, there was no checking that the characters
used in the name of a netCDF object were compatible with CDL
restrictions. The ncdump and ncgen utilities now properly escape and
handle escaped special characters in names, so that all valid netCDF
names are representable in CDL.

@section Other Changes 

There are two new functions in netCDF-3 that don't
correspond to any netCDF-2 functions: nc_inq_libvers and
nc_strerror. The version of the netCDF library in use is returned as a
string by nc_inq_libvers. An error message corresponding to the status
returned by a netCDF function call is returned as a string by the
nc_strerror function.

A new NC_SHARE flag is available for use in an nc_open or nc_create
call, to suppress the default buffering of accesses. The use of
NC_SHARE for concurrent access to a netCDF dataset means you don't
have to call nc_sync after every access to make sure that disk updates
are synchronous. It is important to note that changes to ancillary
data, such as attribute values, are not propagated automatically by
use of the NC_SHARE flag. Use of the nc_sync function is still
required for this purpose.

The version 2 interface had a single inquiry function, ncvarinq for
getting the name, type, and shape of a variable. Similarly, only a
single inquiry function was available for getting information about a
dimension, an attribute, or a netCDF dataset. When you only wanted a
subset of this information, you had to provide NULL arguments as
placeholders for the unneeded information. The new interface includes
additional inquire functions that return each item separately, so
errors are less likely from miscounting arguments.

The previous implementation returned an error when 0-valued count
components were specified in ncvarput and ncvarget calls. This
restriction has been removed, so that now functions in the nc_put_var
and nc_get_var families may be called with 0-valued count components,
resulting in no data being accessed. Although this may seem useless,
it simplifies some programs to not treat 0-valued counts as a special
case.

The previous implementation returned an error when the same dimension
was used more than once in specifying the shape of a variable in
ncvardef. This restriction is relaxed in the netCDF-3 implementation,
because an auto-correlation matrix is a good example where using the
same dimension twice makes sense.

In the new interface, units for the imap argument to the nc_put_varm
and nc_get_varm families of functions are now in terms of the number
of data elements of the desired internal type, not in terms of bytes
as in the netCDF version-2 mapped access interfaces.

Following is a table of netCDF-2 function names and names of the
corresponding netCDF-3 functions. For parameter lists of netCDF-2
functions, see the netCDF-2 User's Guide.

@table @code

@item ncabort
nc_abort
 
@item ncattcopy
nc_copy_att
 
@item ncattdel
nc_del_att
 
@item ncattget
nc_get_att_double, nc_get_att_float, nc_get_att_int, nc_get_att_long,
nc_get_att_schar, nc_get_att_short, nc_get_att_text, nc_get_att_uchar
 
@item ncattinq
nc_inq_att, nc_inq_attid, nc_inq_attlen, nc_inq_atttype
 
@item ncattname
nc_inq_attname
 
@item ncattput
nc_put_att_double, nc_put_att_float, nc_put_att_int, nc_put_att_long,
nc_put_att_schar, nc_put_att_short, nc_put_att_text, nc_put_att_uchar
 
@item ncattrename
nc_rename_att
 
@item ncclose
nc_close
 
@item nccreate
nc_create
 
@item ncdimdef
nc_def_dim
 
@item ncdimid
nc_inq_dimid
 
@item ncdiminq
nc_inq_dim, nc_inq_dimlen, nc_inq_dimname
 
@item ncdimrename
nc_rename_dim
 
@item ncendef
nc_enddef
 
@item ncinquire
nc_inq, nc_inq_natts, nc_inq_ndims, nc_inq_nvars, nc_inq_unlimdim
 
@item ncopen
nc_open
 
@item ncrecget
(none)
 
@item ncrecinq
(none)
 
@item ncrecput
(none)
 
@item ncredef
nc_redef
 
@item ncsetfill
nc_set_fill
 
@item ncsync
nc_sync
 
@item nctypelen
(none)
 
@item ncvardef
nc_def_var
 
@item ncvarget
nc_get_vara_double, nc_get_vara_float, nc_get_vara_int,
nc_get_vara_long, nc_get_vara_schar, nc_get_vara_short,
nc_get_vara_text, nc_get_vara_uchar
 
@item ncvarget1
nc_get_var1_double, nc_get_var1_float, nc_get_var1_int,
nc_get_var1_long, nc_get_var1_schar, nc_get_var1_short,
nc_get_var1_text, nc_get_var1_uchar
 
@item ncvargetg
nc_get_varm_double, nc_get_varm_float, nc_get_varm_int,
nc_get_varm_long, nc_get_varm_schar, nc_get_varm_short,
nc_get_varm_text, nc_get_varm_uchar, nc_get_vars_double,
nc_get_vars_float, nc_get_vars_int, nc_get_vars_long,
nc_get_vars_schar, nc_get_vars_short, nc_get_vars_text,
nc_get_vars_uchar
 
@item ncvarid
nc_inq_varid
 
@item ncvarinq
nc_inq_var, nc_inq_vardimid, nc_inq_varname, nc_inq_varnatts,
nc_inq_varndims, nc_inq_vartype
 
@item ncvarput
nc_put_vara_double, nc_put_vara_float, nc_put_vara_int,
nc_put_vara_long, nc_put_vara_schar, nc_put_vara_short,
nc_put_vara_text, nc_put_vara_uchar
 
@item ncvarput1
nc_put_var1_double, nc_put_var1_float, nc_put_var1_int,
nc_put_var1_long, nc_put_var1_schar, nc_put_var1_short,
nc_put_var1_text, nc_put_var1_uchar
 
@item ncvarputg
nc_put_varm_double, nc_put_varm_float, nc_put_varm_int,
nc_put_varm_long, nc_put_varm_schar, nc_put_varm_short,
nc_put_varm_text, nc_put_varm_uchar, nc_put_vars_double,
nc_put_vars_float, nc_put_vars_int, nc_put_vars_long,
nc_put_vars_schar, nc_put_vars_short, nc_put_vars_text,
nc_put_vars_uchar
 
@item ncvarrename
nc_rename_var
 
@item (none)
nc_inq_libvers
 
@item (none)
nc_strerror

@end table

@node NetCDF-3 Error Codes, NetCDF-4 Error Codes, NetCDF 2 C Transition Guide, Top
@appendix NetCDF-3 Error Codes
@cindex error codes, netcdf-3
@cindex netcdf-3 error codes

@example
#define NC_NOERR        0       /* No Error */

#define NC_EBADID       (-33)   /* Not a netcdf id */
#define NC_ENFILE       (-34)   /* Too many netcdfs open */
#define NC_EEXIST       (-35)   /* netcdf file exists && NC_NOCLOBBER */
#define NC_EINVAL       (-36)   /* Invalid Argument */
#define NC_EPERM        (-37)   /* Write to read only */
#define NC_ENOTINDEFINE (-38)   /* Operation not allowed in data mode */
#define NC_EINDEFINE    (-39)   /* Operation not allowed in define mode */
#define NC_EINVALCOORDS (-40)   /* Index exceeds dimension bound */
#define NC_EMAXDIMS     (-41)   /* NC_MAX_DIMS exceeded */
#define NC_ENAMEINUSE   (-42)   /* String match to name in use */
#define NC_ENOTATT      (-43)   /* Attribute not found */
#define NC_EMAXATTS     (-44)   /* NC_MAX_ATTRS exceeded */
#define NC_EBADTYPE     (-45)   /* Not a netcdf data type */
#define NC_EBADDIM      (-46)   /* Invalid dimension id or name */
#define NC_EUNLIMPOS    (-47)   /* NC_UNLIMITED in the wrong index */
#define NC_EMAXVARS     (-48)   /* NC_MAX_VARS exceeded */
#define NC_ENOTVAR      (-49)   /* Variable not found */
#define NC_EGLOBAL      (-50)   /* Action prohibited on NC_GLOBAL varid */
#define NC_ENOTNC       (-51)   /* Not a netcdf file */
#define NC_ESTS         (-52)   /* In Fortran, string too short */
#define NC_EMAXNAME     (-53)   /* NC_MAX_NAME exceeded */
#define NC_EUNLIMIT     (-54)   /* NC_UNLIMITED size already in use */
#define NC_ENORECVARS   (-55)   /* nc_rec op when there are no record vars */
#define NC_ECHAR        (-56)   /* Attempt to convert between text & numbers */
#define NC_EEDGE        (-57)   /* Edge+start exceeds dimension bound */
#define NC_ESTRIDE      (-58)   /* Illegal stride */
#define NC_EBADNAME     (-59)   /* Attribute or variable name
                                         contains illegal characters */
/* N.B. following must match value in ncx.h */
#define NC_ERANGE       (-60)   /* Math result not representable */
#define NC_ENOMEM       (-61)   /* Memory allocation (malloc) failure */

#define NC_EVARSIZE     (-62)   /* One or more variable sizes violate
                                   format constraints */ 
#define NC_EDIMSIZE     (-63)   /* Invalid dimension size */
#define NC_ETRUNC       (-64)   /* File likely truncated or possibly corrupted */
@end example

@node NetCDF-4 Error Codes, DAP Error Codes, NetCDF-3 Error Codes, Top
@appendix NetCDF-4 Error Codes
@cindex error codes, netcdf-4
@cindex netcdf-4 error codes

NetCDF-4 uses all error codes from NetCDF-3 (@pxref{NetCDF-3 Error
Codes}). The following additional error codes were added for new
errors unique to netCDF-4.

@example
#define NC_EHDFERR       (-101)
#define NC_ECANTREAD     (-102)
#define NC_ECANTWRITE    (-103)
#define NC_ECANTCREATE   (-104)
#define NC_EFILEMETA     (-105)
#define NC_EDIMMETA      (-106)
#define NC_EATTMETA      (-107)
#define NC_EVARMETA      (-108)
#define NC_ENOCOMPOUND   (-109)
#define NC_EATTEXISTS    (-110)
#define NC_ENOTNC4       (-111) /* Attempting netcdf-4 operation on netcdf-3 file. */  
#define NC_ESTRICTNC3    (-112) /* Attempting netcdf-4 operation on strict nc3 netcdf-4 file. */  
#define NC_EBADGRPID     (-113) /* Bad group id. Bad! */
#define NC_EBADTYPEID    (-114) /* Bad type id. */
#define NC_EBADFIELDID   (-115) /* Bad field id. */
#define NC_EUNKNAME      (-116)
@end example

@node DAP Error Codes, Combined Index, NetCDF-4 Error Codes, Top
@appendix DAP Error Codes
@cindex error codes, DAP
@cindex DAP error codes

If the DAP client is enabled, then the following additional
error codes may occur.

@example
#define NC_EDAP         (-66)   /* Generic DAP error */
#define NC_ECURL        (-67)   /* Generic libcurl error */
#define NC_EIO          (-68)   /* Generic IO error */
#define NC_ENODATA      (-69)   /* Attempt to access variable with no data */
#define NC_EDAPSVC      (-70)   /* DAP Server side error */
#define NC_EDAS         (-71)   /* Malformed or inaccessible DAS */
#define NC_EDDS         (-72)   /* Malformed or inaccessible DDS */
#define NC_EDATADDS     (-73)   /* Malformed or inaccessible DATADDS */
#define NC_EDAPURL      (-74)   /* Malformed DAP URL */
#define NC_EDAPCONSTRAINT (-75) /* Malformed DAP Constraint*/
#define NC_EDAP         (-66)   /* Generic DAP error */
#define NC_ECURL        (-67)   /* Generic libcurl error */
#define NC_EIO          (-68)   /* Generic IO error */
#define NC_ENODATA      (-69)   /* Attempt to access variable with no data */
#define NC_EDAPSVC      (-70)   /* DAP Server side error */
#define NC_EDAS         (-71)   /* Malformed or inaccessible DAS */
#define NC_EDDS         (-72)   /* Malformed or inaccessible DDS */
#define NC_EDATADDS     (-73)   /* Malformed or inaccessible DATADDS */
#define NC_EDAPURL      (-74)   /* Malformed DAP URL */
#define NC_EDAPCONSTRAINT (-75) /* Malformed DAP Constraint*/
@end example

@node Combined Index,  , DAP Error Codes, Top
@chapter Index

@printindex cp

@bye
End: