netcdf-c/libdispatch/datt.c

/** \file
Attribute functions

These functions read and write attributes.

Copyright 2010 University Corporation for Atmospheric
Research/Unidata. See \ref copyright file for more info.  */

#include "ncdispatch.h"

/** \defgroup attributes Attributes

Attributes hold metadata about data and files.

\image html ncatts.png "Attributes store metadata."

Attributes may be associated with a 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:
- Create an attribute, given its variable ID, name, data type, length,
  and value.
- Get attribute's data type and length from its variable ID and name.
- Get attribute's value from its variable ID and name.
- Copy attribute from one netCDF variable to another.
- Get name of attribute from its number.
- Rename an attribute.
- Delete an attribute. 
*/

/*! \{*/ /* All these functions are part of the above defgroup... */


/** \name Deleting and Renaming Attributes

Functions to delete or rename an attribute. */
/*! \{ */ /* All these functions are part of this named group... */

/*!
Rename an attribute.

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.

\param 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().

\param varid Variable ID of the attribute's variable, or ::NC_GLOBAL for
a global attribute.

\param name Attribute \ref object_name. 

\param newname The new attribute \ref object_name. 

<h1>Example</h1>

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:

\code
     #include <netcdf.h>
        ...
     int  status;
     int  ncid;  
     int  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);
        ...
     status = nc_rename_att(ncid, rh_id, "units", "Units");
     if (status != NC_NOERR) handle_error(status);
\endcode
 */
int
nc_rename_att(int ncid, int varid, const char *name, const char *newname)
{
   NC* ncp;
   int stat = NC_check_id(ncid, &ncp);
   if(stat != NC_NOERR) return stat;
   return ncp->dispatch->rename_att(ncid, varid, name, newname);
}

/*!
Delete an attribute.

The function nc_del_att() deletes a netCDF attribute from an open
netCDF dataset. The netCDF dataset must be in define mode.

\param 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().

\param varid Variable ID of the attribute's variable, or ::NC_GLOBAL
for a global attribute.

\param name Attribute name. 

<h1>Example</h1>

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:

\code
     #include <netcdf.h>
        ...
     int  status;     
     int  ncid;      
     int  rh_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);
        ...
     status = nc_redef(ncid); 
     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);
     if (status != NC_NOERR) handle_error(status);
\endcode
 */
int
nc_del_att(int ncid, int varid, const char *name)
{
   NC* ncp;
   int stat = NC_check_id(ncid, &ncp);
   if(stat != NC_NOERR) return stat;
   return ncp->dispatch->del_att(ncid, varid, name);
}
/*! \} */  /* End of named group ...*/

/*! \} */ /* End of defgroup. */