netcdf-c/libdispatch/dfile.c

/**
 * @file
 *
 * File create and open functions
 *
 * These functions end up calling functions in one of the dispatch
 * layers (netCDF-4, dap server, etc).
 *
 * Copyright 2018 University Corporation for Atmospheric
 * Research/Unidata. See COPYRIGHT file for more info.
 */

#include "config.h"
#include <stdlib.h>
#ifdef HAVE_STRING_H
#include <string.h>
#endif
#ifdef HAVE_SYS_RESOURCE_H
#include <sys/resource.h>
#endif
#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
#ifdef HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif

#ifdef HAVE_UNISTD_H
#include <unistd.h> /* lseek() */
#endif

#ifdef HAVE_STDIO_H
#include <stdio.h>
#endif

#include "ncdispatch.h"
#include "netcdf_mem.h"
#include "ncwinpath.h"
#include "fbits.h"

#undef DEBUG

extern int NC_initialized; /**< True when dispatch table is initialized. */

/* User-defined formats. */
NC_Dispatch *UDF0_dispatch_table = NULL;
char UDF0_magic_number[NC_MAX_MAGIC_NUMBER_LEN + 1] = "";
NC_Dispatch *UDF1_dispatch_table = NULL;
char UDF1_magic_number[NC_MAX_MAGIC_NUMBER_LEN + 1] = "";

/**************************************************/


/** \defgroup datasets NetCDF File and Data I/O

    NetCDF opens datasets as files or remote access URLs.

    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:
    - Get version of library.
    - Get error message corresponding to a returned error code.

    The operations supported on a netCDF dataset as a single object are:
    - Create, given dataset name and whether to overwrite or not.
    - Open for access, given dataset name and read or write intent.
    - Put into define mode, to add dimensions, variables, or attributes.
    - Take out of define mode, checking consistency of additions.
    - Close, writing to disk if required.
    - Inquire about the number of dimensions, number of variables,
    number of global attributes, and ID of the unlimited dimension, if
    any.
    - Synchronize to disk to make sure it is current.
    - Set and unset nofill mode for optimized sequential writes.
    - 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.
*/

/**
 * Add handling of user-defined format.
 *
 * User-defined formats allow users to write a library which can read
 * their own proprietary format as if it were netCDF. This allows
 * existing netCDF codes to work on non-netCDF data formats.
 *
 * User-defined formats work by specifying a netCDF dispatch
 * table. The dispatch table is a struct of (mostly) C function
 * pointers. It contains pointers to the key functions of the netCDF
 * API. Once these functions are provided, and the dispatch table is
 * specified, the netcdf-c library can read any format.
 *
 * @note Unlike the public netCDF API, the dispatch table may not be
 * backward compatible between netCDF releases. Instead, it contains a
 * dispatch version number. If this number is not correct (i.e. does
 * not match the current dispatch table version), then ::NC_EINVAL
 * will be returned.
 *
 * @param mode_flag NC_UDF0 or NC_UDF1
 * @param dispatch_table Pointer to dispatch table to use for this user format.
 * @param magic_number Magic number used to identify file. Ignored if
 * NULL.
 *
 * @return ::NC_NOERR No error.
 * @return ::NC_EINVAL Invalid input.
 * @author Ed Hartnett
 * @ingroup datasets
 */
int
nc_def_user_format(int mode_flag, NC_Dispatch *dispatch_table, char *magic_number)
{
    /* Check inputs. */
    if (mode_flag != NC_UDF0 && mode_flag != NC_UDF1)
        return NC_EINVAL;
    if (!dispatch_table)
        return NC_EINVAL;
    if (magic_number && strlen(magic_number) > NC_MAX_MAGIC_NUMBER_LEN)
        return NC_EINVAL;

    /* Check the version of the dispatch table provided. */
    if (dispatch_table->dispatch_version != NC_DISPATCH_VERSION)
        return NC_EINVAL;

    /* Retain a pointer to the dispatch_table and a copy of the magic
     * number, if one was provided. */
    switch(mode_flag)
    {
    case NC_UDF0:
        UDF0_dispatch_table = dispatch_table;
        if (magic_number)
            strncpy(UDF0_magic_number, magic_number, NC_MAX_MAGIC_NUMBER_LEN);
        break;
    case NC_UDF1:
        UDF1_dispatch_table = dispatch_table;
        if (magic_number)
            strncpy(UDF1_magic_number, magic_number, NC_MAX_MAGIC_NUMBER_LEN);
        break;
    }

    return NC_NOERR;
}

/**
 * Inquire about user-defined format.
 *
 * @param mode_flag NC_UDF0 or NC_UDF1
 * @param dispatch_table Pointer that gets pointer to dispatch table
 * to use for this user format, or NULL if this user-defined format is
 * not defined. Ignored if NULL.
 * @param magic_number Pointer that gets magic number used to identify
 * file, if one has been set. Magic number will be of max size
 * NC_MAX_MAGIC_NUMBER_LEN. Ignored if NULL.
 *
 * @return ::NC_NOERR No error.
 * @return ::NC_EINVAL Invalid input.
 * @author Ed Hartnett
 * @ingroup datasets
 */
int
nc_inq_user_format(int mode_flag, NC_Dispatch **dispatch_table, char *magic_number)
{
    /* Check inputs. */
    if (mode_flag != NC_UDF0 && mode_flag != NC_UDF1)
        return NC_EINVAL;

    switch(mode_flag)
    {
    case NC_UDF0:
        if (dispatch_table)
            *dispatch_table = UDF0_dispatch_table;
        if (magic_number)
            strncpy(magic_number, UDF0_magic_number, NC_MAX_MAGIC_NUMBER_LEN);
        break;
    case NC_UDF1:
        if (dispatch_table)
            *dispatch_table = UDF1_dispatch_table;
        if (magic_number)
            strncpy(magic_number, UDF1_magic_number, NC_MAX_MAGIC_NUMBER_LEN);
        break;
    }

    return NC_NOERR;
}

/**  \ingroup datasets
     Create a new netCDF file.

     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.

     \param path The file name of the new netCDF dataset.

     \param cmode The creation mode flag. The following flags are available:
     NC_CLOBBER (overwrite existing file),
     NC_NOCLOBBER (do not overwrite existing file),
     NC_SHARE (limit write caching - netcdf classic files only),
     NC_64BIT_OFFSET (create 64-bit offset file),
     NC_64BIT_DATA (alias NC_CDF5) (create CDF-5 file),
     NC_NETCDF4 (create netCDF-4/HDF5 file),
     NC_CLASSIC_MODEL (enforce netCDF classic mode on netCDF-4/HDF5 files),
     NC_DISKLESS (store data in memory), and
     NC_PERSIST (force the NC_DISKLESS data from memory to a file),
     NC_MMAP (use MMAP for NC_DISKLESS instead of NC_INMEMORY -- deprecated).
     See discussion below.

     \param ncidp Pointer to location where returned netCDF ID is to be
     stored.

     <h2>The cmode Flag</h2>

     The cmode flag is used to control the type of file created, and some
     aspects of how it may be used.

     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.

     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. See Large File Support.

     Setting NC_64BIT_DATA (alias NC_CDF5) causes netCDF to create a CDF-5
     file format that supports large files (i.e. over 2GB) and large
     variables (over 2B array elements.). See Large File Support.

     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. See NetCDF Classic Format Limitations.

     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
     CDF-1, 2 and 5 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.

     Setting NC_DISKLESS causes netCDF to create the file only in
     memory and to optionally write the final contents to the
     correspondingly named disk file. This allows for the use of
     files that have no long term purpose. Operating on an existing file
     in memory may also be faster. The decision on whether
     or not to "persist" the memory contents to a disk file is
     described in detail in the file docs/inmemory.md, which is
     definitive.  By default, closing a diskless fill will cause it's
     contents to be lost.

     If NC_DISKLESS is going to be used for creating a large classic
     file, it behooves one to use nc__create and specify an
     appropriately large value of the initialsz parameter to avoid to
     many extensions to the in-memory space for the file.  This flag
     applies to files in classic format and to file in extended
     format (netcdf-4).

     Note that nc_create(path,cmode,ncidp) is equivalent to the invocation of
     nc__create(path,cmode,NC_SIZEHINT_DEFAULT,NULL,ncidp).

     \returns ::NC_NOERR No error.
     \returns ::NC_EEXIST Specifying a file name of a file that exists and also specifying NC_NOCLOBBER.
     \returns ::NC_EPERM Attempting to create a netCDF file in a directory where you do not have permission to create files.
     \returns ::NC_ENOMEM System out of memory.
     \returns ::NC_ENFILE Too many files open.
     \returns ::NC_EHDFERR HDF5 error (netCDF-4 files only).
     \returns ::NC_EFILEMETA Error writing netCDF-4 file-level metadata in
     HDF5 file. (netCDF-4 files only).
     \returns ::NC_EDISKLESS if there was an error in creating the
     in-memory file.

     \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.

     <h1>Examples</h1>

     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:

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

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

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

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

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

     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.

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

     In this example we create an in-memory netCDF classic dataset named
     diskless.nc whose content will be lost when nc_close() is called.

     @code
     #include <netcdf.h>
     ...
     int status = NC_NOERR;
     int ncid;
     ...
     status = nc_create("diskless.nc", NC_DISKLESS, &ncid);
     if (status != NC_NOERR) handle_error(status);
     @endcode

     In this example we create a in-memory netCDF classic dataset named
     diskless.nc and specify that it should be made persistent
     in a file named diskless.nc when nc_close() is called.

     @code
     #include <netcdf.h>
     ...
     int status = NC_NOERR;
     int ncid;
     ...
     status = nc_create("diskless.nc", NC_DISKLESS|NC_PERSIST, &ncid);
     if (status != NC_NOERR) handle_error(status);
     @endcode

     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.  */
int
nc_create(const char *path, int cmode, int *ncidp)
{
    return nc__create(path,cmode,NC_SIZEHINT_DEFAULT,NULL,ncidp);
}

/**
 * Create a netCDF file with some extra parameters controlling classic
 * file caching.
 *
 * Like nc_create(), this function creates a netCDF file.
 *
 * @param path The file name of the new netCDF dataset.
 * @param cmode The creation mode flag, the same as in nc_create().
 * @param 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. This only applies to classic CDF-1, 2, and 5 files.  The
 * special value NC_SIZEHINT_DEFAULT (which is the value 0), lets the
 * netcdf library choose a suitable initial size.
 * @param chunksizehintp A pointer to the chunk size hint, which
 * 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
 * a NULL pointer or having the pointer point to 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. This only applies to classic files.
 * @param ncidp Pointer to location where returned netCDF ID is to be
 * stored.
 *
 * @note This function uses the same return codes as the nc_create()
 * function.
 *
 * @returns ::NC_NOERR No error.
 * @returns ::NC_ENOMEM System out of memory.
 * @returns ::NC_EHDFERR HDF5 error (netCDF-4 files only).
 * @returns ::NC_EFILEMETA Error writing netCDF-4 file-level metadata in
 * HDF5 file. (netCDF-4 files only).
 * @returns ::NC_EDISKLESS if there was an error in creating the
 * in-memory file.
 *
 * <h1>Examples</h1>
 *
 * 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.
 *
 * @code
 #include <netcdf.h>
 ...
 int status = NC_NOERR;
 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);
 @endcode
 *
 * @ingroup datasets
 * @author Glenn Davis
 */
int
nc__create(const char *path, int cmode, size_t initialsz,
           size_t *chunksizehintp, int *ncidp)
{
    return NC_create(path, cmode, initialsz, 0,
                     chunksizehintp, 0, NULL, ncidp);
}

/** \ingroup datasets
    Create a netCDF file with the contents stored in memory.

    \param path Must be non-null, but otherwise only used to set the dataset name.

    \param mode the mode flags; Note that this procedure uses a limited set of flags because it forcibly sets NC_INMEMORY.

    \param initialsize (advisory) size to allocate for the created file

    \param ncidp Pointer to location where returned netCDF ID is to be
    stored.

    \returns ::NC_NOERR No error.

    \returns ::NC_ENOMEM Out of memory.

    \returns ::NC_EDISKLESS diskless io is not enabled for fails.

    \returns ::NC_EINVAL, etc. other errors also returned by nc_open.

    <h1>Examples</h1>

    In this example we use nc_create_mem() to create a classic netCDF dataset
    named foo.nc. The initial size is set to 4096.

    @code
    #include <netcdf.h>
    ...
    int status = NC_NOERR;
    int ncid;
    int mode = 0;
    size_t initialsize = 4096;
    ...
    status = nc_create_mem("foo.nc", mode, initialsize, &ncid);
    if (status != NC_NOERR) handle_error(status);
    @endcode
*/

int
nc_create_mem(const char* path, int mode, size_t initialsize, int* ncidp)
{
    if(mode & NC_MMAP) return NC_EINVAL;
    mode |= NC_INMEMORY; /* Specifically, do not set NC_DISKLESS */
    return NC_create(path, mode, initialsize, 0, NULL, 0, NULL, ncidp);
}

/**
 * @internal Create a file with special (deprecated) Cray settings.
 *
 * @deprecated This function was used in the old days with the Cray at
 * NCAR. The Cray is long gone, and this call is supported only for
 * backward compatibility. Use nc_create() instead.
 *
 * @param path File name.
 * @param cmode Create mode.
 * @param initialsz Initial size of metadata region for classic files,
 * ignored for other files.
 * @param basepe Deprecated parameter from the Cray days.
 * @param chunksizehintp A pointer to the chunk size hint. This only
 * applies to classic files.
 * @param ncidp Pointer that gets ncid.
 *
 * @return ::NC_NOERR No error.
 * @author Glenn Davis
 */
int
nc__create_mp(const char *path, int cmode, size_t initialsz,
              int basepe, size_t *chunksizehintp, int *ncidp)
{
    return NC_create(path, cmode, initialsz, basepe,
                     chunksizehintp, 0, NULL, ncidp);
}

/**
 * Open an existing netCDF file.
 *
 * This function opens an existing netCDF dataset for access. It
 * determines the underlying file format automatically. Use the same
 * call to open a netCDF classic or netCDF-4 file.
 *
 * @param path File name for netCDF dataset to be opened. When the dataset
 * is located on some remote server, then the path may be an OPeNDAP URL
 * rather than a file path.
 * @param omode The open mode flag may include NC_WRITE (for read/write
 * access) and NC_SHARE (see below) and NC_DISKLESS (see below).
 * @param ncidp Pointer to location where returned netCDF ID is to be
 * stored.
 *
 * <h2>Open Mode</h2>
 *
 * 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
 * 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.
 *
 * This procedure may also be invoked with the NC_DISKLESS flag set in
 * the omode argument if the file to be opened is a classic format
 * file.  For nc_open(), this flag applies only to files in classic
 * format.  If the file is of type NC_NETCDF4, then the NC_DISKLESS
 * flag will be ignored.
 *
 * If NC_DISKLESS is specified, then the whole file is read completely
 * into memory. In effect this creates an in-memory cache of the file.
 * If the omode flag also specifies NC_PERSIST, then the in-memory cache
 * will be re-written to the disk file when nc_close() is called.  For
 * some kinds of manipulations, having the in-memory cache can speed
 * up file processing. But in simple cases, non-cached processing may
 * actually be faster than using cached processing.  You will need to
 * experiment to determine if the in-memory caching is worthwhile for
 * your application.
 *
 * Normally, NC_DISKLESS allocates space in the heap for storing the
 * in-memory file. If, however, the ./configure flags --enable-mmap is
 * used, and the additional omode flag NC_MMAP is specified, then the
 * file will be opened using the operating system MMAP facility.  This
 * flag only applies to files in classic format. Extended format
 * (netcdf-4) files will ignore the NC_MMAP flag.
 *
 * In most cases, using MMAP provides no advantage for just
 * NC_DISKLESS. The one case where using MMAP is an advantage is when
 * a file is to be opened and only a small portion of its data is to
 * be read and/or written.  In this scenario, MMAP will cause only the
 * accessed data to be retrieved from disk. Without MMAP, NC_DISKLESS
 * will read the whole file into memory on nc_open. Thus, MMAP will
 * provide some performance improvement in this case.
 *
 * 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.
 *
 * As of version 4.3.1.2, multiple calls to nc_open with the same
 * path will return the same ncid value.
 *
 * @note 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:
 *
 * Note that nc_open(path,omode,ncidp) is equivalent to the invocation
 * of nc__open(path,omode,NC_SIZEHINT_DEFAULT,NULL,ncidp).
 *
 * @returns ::NC_NOERR No error.
 * @returns ::NC_EPERM Attempting to create a netCDF file in a directory where you do not have permission to open files.
 * @returns ::NC_ENFILE Too many files open
 * @returns ::NC_ENOMEM Out of memory.
 * @returns ::NC_EHDFERR HDF5 error. (NetCDF-4 files only.)
 * @returns ::NC_EDIMMETA Error in netCDF-4 dimension metadata. (NetCDF-4 files only.)
 *
 * <h1>Examples</h1>
 *
 * Here is an example using nc_open()to open an existing netCDF dataset
 * named foo.nc for read-only, non-shared access:
 *
 * @code
 * #include <netcdf.h>
 *   ...
 * int status = NC_NOERR;
 * int ncid;
 *   ...
 * status = nc_open("foo.nc", 0, &ncid);
 * if (status != NC_NOERR) handle_error(status);
 * @endcode
 * @ingroup datasets
 * @author Glenn Davis, Ed Hartnett, Dennis Heimbigner
 */
int
nc_open(const char *path, int omode, int *ncidp)
{
    return NC_open(path, omode, 0, NULL, 0, NULL, ncidp);
}

/** \ingroup datasets
    Open a netCDF file with extra performance parameters for the classic
    library.

    \param 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.

    \param omode The open mode flag may include NC_WRITE (for read/write
    access) and NC_SHARE as in nc_open().

    \param chunksizehintp A size hint for the classic library. Only
    applies to classic files. See below for more
    information.

    \param ncidp Pointer to location where returned netCDF ID is to be
    stored.

    <h1>The chunksizehintp Parameter</h1>

    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 a NULL pointer or having the pointer point to 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.


    \returns ::NC_NOERR No error.

    \returns ::NC_ENOMEM Out of memory.

    \returns ::NC_EHDFERR HDF5 error. (NetCDF-4 files only.)

    \returns ::NC_EDIMMETA Error in netCDF-4 dimension metadata. (NetCDF-4
    files only.)

*/
int
nc__open(const char *path, int omode,
         size_t *chunksizehintp, int *ncidp)
{
    /* this API is for non-parallel access.
     * Note nc_open_par() also calls NC_open().
     */
    return NC_open(path, omode, 0, chunksizehintp, 0, NULL, ncidp);
}

/** \ingroup datasets
    Open a netCDF file with the contents taken from a block of memory.

    \param path Must be non-null, but otherwise only used to set the dataset name.

    \param omode the open mode flags; Note that this procedure uses a limited set of flags because it forcibly sets NC_INMEMORY.

    \param size The length of the block of memory being passed.

    \param memory Pointer to the block of memory containing the contents
    of a netcdf file.

    \param ncidp Pointer to location where returned netCDF ID is to be
    stored.

    \returns ::NC_NOERR No error.

    \returns ::NC_ENOMEM Out of memory.

    \returns ::NC_EDISKLESS diskless io is not enabled for fails.

    \returns ::NC_EINVAL, etc. other errors also returned by nc_open.

    <h1>Examples</h1>

    Here is an example using nc_open_mem() to open an existing netCDF dataset
    named foo.nc for read-only, non-shared access. It differs from the nc_open()
    example in that it assumes the contents of foo.nc have been read into memory.

    @code
    #include <netcdf.h>
    #include <netcdf_mem.h>
    ...
    int status = NC_NOERR;
    int ncid;
    size_t size;
    void* memory;
    ...
    size = <compute file size of foo.nc in bytes>;
    memory = malloc(size);
    ...
    status = nc_open_mem("foo.nc", 0, size, memory, &ncid);
    if (status != NC_NOERR) handle_error(status);
    @endcode
*/
int
nc_open_mem(const char* path, int omode, size_t size, void* memory, int* ncidp)
{
    NC_memio meminfo;

    /* Sanity checks */
    if(memory == NULL || size < MAGIC_NUMBER_LEN || path == NULL)
        return NC_EINVAL;
    if(omode & (NC_WRITE|NC_MMAP))
        return NC_EINVAL;
    omode |= (NC_INMEMORY); /* Note: NC_INMEMORY and NC_DISKLESS are mutually exclusive*/
    meminfo.size = size;
    meminfo.memory = memory;
    meminfo.flags = NC_MEMIO_LOCKED;
    return NC_open(path, omode, 0, NULL, 0, &meminfo, ncidp);
}

/** \ingroup datasets
    Open a netCDF file with the contents taken from a block of memory.
    Similar to nc_open_mem, but with parameters. Warning: if you do
    specify that the provided memory is locked, then <b>never</b>
    pass in non-heap allocated memory. Additionally, if not locked,
    then do not assume that the memory returned by nc_close_mem
    is the same as passed to nc_open_memio. You <b>must</b> check
    before attempting to free the original memory.

    \param path Must be non-null, but otherwise only used to set the dataset name.

    \param omode the open mode flags; Note that this procedure uses a limited set of flags because it forcibly sets NC_INMEMORY.

    \param params controlling parameters

    \param ncidp Pointer to location where returned netCDF ID is to be
    stored.

    \returns ::NC_NOERR No error.

    \returns ::NC_ENOMEM Out of memory.

    \returns ::NC_EDISKLESS diskless io is not enabled for fails.

    \returns ::NC_EINVAL, etc. other errors also returned by nc_open.

    <h1>Examples</h1>

    Here is an example using nc_open_memio() to open an existing netCDF dataset
    named foo.nc for read-only, non-shared access. It differs from the nc_open_mem()
    example in that it uses a parameter block.

    @code
    #include <netcdf.h>
    #include <netcdf_mem.h>
    ...
    int status = NC_NOERR;
    int ncid;
    NC_memio params;
    ...
    params.size = <compute file size of foo.nc in bytes>;
    params.memory = malloc(size);
    params.flags = <see netcdf_mem.h>
    ...
    status = nc_open_memio("foo.nc", 0, &params, &ncid);
    if (status != NC_NOERR) handle_error(status);
    @endcode
*/
int
nc_open_memio(const char* path, int omode, NC_memio* params, int* ncidp)
{
    /* Sanity checks */
    if(path == NULL || params == NULL)
        return NC_EINVAL;
    if(params->memory == NULL || params->size < MAGIC_NUMBER_LEN)
        return NC_EINVAL;

    if(omode & NC_MMAP)
        return NC_EINVAL;
    omode |= (NC_INMEMORY);
    return NC_open(path, omode, 0, NULL, 0, params, ncidp);
}

/**
 * @internal Open a netCDF file with extra parameters for Cray.
 *
 * @deprecated This function was used in the old days with the Cray at
 * NCAR. The Cray is long gone, and this call is supported only for
 * backward compatibility. Use nc_open() instead.
 *
 * @param path The file name of the new netCDF dataset.
 * @param omode Open mode.
 * @param basepe Deprecated parameter from the Cray days.
 * @param chunksizehintp A pointer to the chunk size hint. This only
 * applies to classic files.
 * @param ncidp Pointer to location where returned netCDF ID is to be
 * stored.
 *
 * @return ::NC_NOERR
 * @author Glenn Davis
 */
int
nc__open_mp(const char *path, int omode, int basepe,
            size_t *chunksizehintp, int *ncidp)
{
    return NC_open(path, omode, basepe, chunksizehintp, 0, NULL, ncidp);
}

/** \ingroup datasets
    Get the file pathname (or the opendap URL) which was used to
    open/create the ncid's file.

    \param ncid NetCDF ID, from a previous call to nc_open() or
    nc_create().

    \param pathlen Pointer where length of path will be returned. Ignored
    if NULL.

    \param path Pointer where path name will be copied. Space must already
    be allocated. Ignored if NULL.

    \returns ::NC_NOERR No error.

    \returns ::NC_EBADID Invalid ncid passed.
*/
int
nc_inq_path(int ncid, size_t *pathlen, char *path)
{
    NC* ncp;
    int stat = NC_NOERR;
    if ((stat = NC_check_id(ncid, &ncp)))
        return stat;
    if(ncp->path == NULL) {
        if(pathlen) *pathlen = 0;
        if(path) path[0] = '\0';
    } else {
        if (pathlen) *pathlen = strlen(ncp->path);
        if (path) strcpy(path, ncp->path);
    }
    return stat;
}

/** \ingroup datasets
    Put open netcdf dataset into define mode

    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.

    For netCDF-4 files (i.e. files created with NC_NETCDF4 in the cmode in
    their call to 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.

    \param ncid NetCDF ID, from a previous call to nc_open() or
    nc_create().

    \returns ::NC_NOERR No error.

    \returns ::NC_EBADID Bad ncid.

    \returns ::NC_EBADGRPID The ncid must refer to the root group of the
    file, that is, the group returned by nc_open() or nc_create().

    \returns ::NC_EINDEFINE Already in define mode.

    \returns ::NC_EPERM File is read-only.

    <h1>Example</h1>

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

    \code
    #include <netcdf.h>
    ...
    int status = NC_NOERR;
    int ncid;
    ...
    status = nc_open("foo.nc", NC_WRITE, &ncid);
    if (status != NC_NOERR) handle_error(status);
    ...
    status = nc_redef(ncid);
    if (status != NC_NOERR) handle_error(status);
    \endcode
*/
int
nc_redef(int ncid)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;
    return ncp->dispatch->redef(ncid);
}

/** \ingroup datasets
    Leave define mode

    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 with 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 File Structure and Performance.

    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.

    \param ncid NetCDF ID, from a previous call to nc_open() or
    nc_create().

    If you use a group id (in a netCDF-4/HDF5 file), the enddef
    will apply to the entire file. That means the enddef will not just end
    define mode in one group, but in the entire file.

    \returns ::NC_NOERR no error

    \returns ::NC_EBADID Invalid ncid passed.

    <h1>Example</h1>

    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:

    \code
    #include <netcdf.h>
    ...
    int status = NC_NOERR;
    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);
    if (status != NC_NOERR) handle_error(status);
    \endcode
*/
int
nc_enddef(int ncid)
{
    int status = NC_NOERR;
    NC *ncp;
    status = NC_check_id(ncid, &ncp);
    if(status != NC_NOERR) return status;
    return ncp->dispatch->_enddef(ncid,0,1,0,1);
}

/** \ingroup datasets
    Leave define mode with performance tuning

    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 with 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 File Structure and Performance.

    \warning 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 classic 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,

    \code
    nc_enddef(ncid);
    \endcode

    is equivalent to

    \code
    nc__enddef(ncid, 0, 4, 0, 4);
    \endcode

    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.

    \param ncid NetCDF ID, from a previous call to nc_open() or
    nc_create().

    \param h_minfree Sets the pad at the end of the "header" section.

    \param v_align Controls the alignment of the beginning of the data
    section for fixed size variables.

    \param v_minfree Sets the pad at the end of the data section for fixed
    size variables.

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

    \returns ::NC_NOERR No error.

    \returns ::NC_EBADID Invalid ncid passed.

*/
int
nc__enddef(int ncid, size_t h_minfree, size_t v_align, size_t v_minfree,
           size_t r_align)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;
    return ncp->dispatch->_enddef(ncid,h_minfree,v_align,v_minfree,r_align);
}

/** \ingroup datasets
    Synchronize an open netcdf dataset to disk

    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:
    - To minimize data loss in case of abnormal termination, or
    - 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.

    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.

    \param ncid NetCDF ID, from a previous call to nc_open() or
    nc_create().

    \returns ::NC_NOERR No error.

    \returns ::NC_EBADID Invalid ncid passed.
*/
int
nc_sync(int ncid)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;
    return ncp->dispatch->sync(ncid);
}

/** \ingroup datasets
    No longer necessary for user to invoke manually.


    \warning Users 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.

    \param ncid NetCDF ID, from a previous call to nc_open() or
    nc_create().

    \returns ::NC_NOERR No error.

    <h1>Example</h1>

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

    \code
    #include <netcdf.h>
    ...
    int ncid, status, latid;
    ...
    status = nc_open("foo.nc", NC_WRITE, &ncid);
    if (status != NC_NOERR) handle_error(status);
    ...
    status = nc_redef(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_abort(ncid);
    if (status != NC_NOERR) handle_error(status);
    }
    \endcode

*/
int
nc_abort(int ncid)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;

    stat = ncp->dispatch->abort(ncid);
    del_from_NCList(ncp);
    free_NC(ncp);
    return stat;
}

/** \ingroup datasets
    Close 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.

    \param ncid NetCDF ID, from a previous call to nc_open() or nc_create().

    \returns ::NC_NOERR No error.

    \returns ::NC_EBADID Invalid id passed.

    \returns ::NC_EBADGRPID ncid did not contain the root group id of this
    file. (NetCDF-4 only).

    <h1>Example</h1>

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

    \code
    #include <netcdf.h>
    ...
    int status = NC_NOERR;
    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);
    if (status != NC_NOERR) handle_error(status);
    \endcode

*/
int
nc_close(int ncid)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;

    stat = ncp->dispatch->close(ncid,NULL);
    /* Remove from the nc list */
    if (!stat)
    {
        del_from_NCList(ncp);
        free_NC(ncp);
    }
    return stat;
}

/** \ingroup datasets
    Do a normal close (see nc_close()) on an in-memory dataset,
    then return a copy of the final memory contents of the dataset.

    \param ncid NetCDF ID, from a previous call to nc_open() or nc_create().

    \param memio a pointer to an NC_memio object into which the final valid memory
    size and memory will be returned.

    \returns ::NC_NOERR No error.

    \returns ::NC_EBADID Invalid id passed.

    \returns ::NC_ENOMEM Out of memory.

    \returns ::NC_EDISKLESS if the file was not created as an inmemory file.

    \returns ::NC_EBADGRPID ncid did not contain the root group id of this
    file. (NetCDF-4 only).

    <h1>Example</h1>

    Here is an example using nc_close_mem to finish the definitions of a new
    netCDF dataset named foo.nc, return the final memory,
    and release its netCDF ID:

    \code
    #include <netcdf.h>
    ...
    int status = NC_NOERR;
    int ncid;
    NC_memio finalmem;
    size_t initialsize = 65000;
    ...
    status = nc_create_mem("foo.nc", NC_NOCLOBBER, initialsize, &ncid);
    if (status != NC_NOERR) handle_error(status);
    ...   create dimensions, variables, attributes
    status = nc_close_memio(ncid,&finalmem);
    if (status != NC_NOERR) handle_error(status);
    \endcode

*/
int
nc_close_memio(int ncid, NC_memio* memio)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;

    stat = ncp->dispatch->close(ncid,memio);
    /* Remove from the nc list */
    if (!stat)
    {
        del_from_NCList(ncp);
        free_NC(ncp);
    }
    return stat;
}

/** \ingroup datasets
    Change the fill-value mode to improve write performance.

    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
    Fill Values. For information about how to define your own fill values
    see Attribute Conventions.

    The behavior corresponding to ::NC_NOFILL overrides the default behavior
    of prefilling data with fill values. This can be used to enhance
    performance, because it avoids the duplicate writes that occur when
    the netCDF library writes fill values that are later overwritten with
    data.

    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 is advantageous to set nofill
    mode:
    - Creating and initializing a netCDF dataset. In this case, you should
    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.
    - 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.
    - 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.

    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.

    \param ncid NetCDF ID, from a previous call to nc_open() or
    nc_create().

    \param fillmode Desired fill mode for the dataset, either ::NC_NOFILL or
    ::NC_FILL.

    \param old_modep Pointer to location for returned current fill mode of
    the dataset before this call, either ::NC_NOFILL or ::NC_FILL.

    \returns ::NC_NOERR No error.

    \returns ::NC_EBADID The specified netCDF ID does not refer to an open
    netCDF dataset.

    \returns ::NC_EPERM The specified netCDF ID refers to a dataset open for
    read-only access.

    \returns ::NC_EINVAL The fill mode argument is neither ::NC_NOFILL nor
    ::NC_FILL.

    <h1>Example</h1>

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

    \code
    #include <netcdf.h>
    ...
    int ncid, status, old_fill_mode;
    ...
    status = nc_open("foo.nc", NC_WRITE, &ncid);
    if (status != NC_NOERR) handle_error(status);

    ...     write data with default prefilling behavior

    status = nc_set_fill(ncid, ::NC_NOFILL, &old_fill_mode);
    if (status != NC_NOERR) handle_error(status);

    ...    write data with no prefilling
    \endcode
*/
int
nc_set_fill(int ncid, int fillmode, int *old_modep)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;
    return ncp->dispatch->set_fill(ncid,fillmode,old_modep);
}

/**
 * @internal Learn base PE.
 *
 * @deprecated This function was used in the old days with the Cray at
 * NCAR. The Cray is long gone, and this call is now meaningless. The
 * value returned for pe is always 0.
 *
 * @param ncid File and group ID.
 * @param pe Pointer for base PE.
 *
 * @return ::NC_NOERR No error.
 * @return ::NC_EBADID Invalid ncid passed.
 * @author Glenn Davis
 */
int
nc_inq_base_pe(int ncid, int *pe)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;
    if (pe) *pe = 0;
    return NC_NOERR;
}

/**
 * @internal Sets base processing element (ignored).
 *
 * @deprecated This function was used in the old days with the Cray at
 * NCAR. The Cray is long gone, and this call is supported only for
 * backward compatibility.
 *
 * @param ncid File ID.
 * @param pe Base PE.
 *
 * @return ::NC_NOERR No error.
 * @return ::NC_EBADID Invalid ncid passed.
 * @author Glenn Davis
 */
int
nc_set_base_pe(int ncid, int pe)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;
    return NC_NOERR;
}

/**
 * @ingroup datasets
 * Inquire about the binary format of a netCDF file
 * as presented by the API.
 *
 * This function returns the (rarely needed) format version.
 *
 * @param ncid NetCDF ID, from a previous call to nc_open() or
 * nc_create().
 * @param formatp Pointer to location for returned format version, one
 * of NC_FORMAT_CLASSIC, NC_FORMAT_64BIT_OFFSET, NC_FORMAT_CDF5,
 * NC_FORMAT_NETCDF4, NC_FORMAT_NETCDF4_CLASSIC.
 *
 * @returns ::NC_NOERR No error.
 * @returns ::NC_EBADID Invalid ncid passed.
 * @author Dennis Heimbigner
 */
int
nc_inq_format(int ncid, int *formatp)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;
    return ncp->dispatch->inq_format(ncid,formatp);
}

/** \ingroup datasets
    Obtain more detailed (vis-a-vis nc_inq_format)
    format information about an open dataset.

    Note that the netcdf API will present the file
    as if it had the format specified by nc_inq_format.
    The true file format, however, may not even be
    a netcdf file; it might be DAP, HDF4, or PNETCDF,
    for example. This function returns that true file type.
    It also returns the effective mode for the file.

    \param ncid NetCDF ID, from a previous call to nc_open() or
    nc_create().

    \param formatp Pointer to location for returned true format.

    \param modep Pointer to location for returned mode flags.

    Refer to the actual list in the file netcdf.h to see the
    currently defined set.

    \returns ::NC_NOERR No error.

    \returns ::NC_EBADID Invalid ncid passed.

*/
int
nc_inq_format_extended(int ncid, int *formatp, int *modep)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;
    return ncp->dispatch->inq_format_extended(ncid,formatp,modep);
}

/**\ingroup datasets
   Inquire about a file or group.

   \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 ndimsp Pointer to location for returned number of dimensions
   defined for this netCDF dataset. Ignored if NULL.

   \param nvarsp Pointer to location for returned number of variables
   defined for this netCDF dataset. Ignored if NULL.

   \param nattsp Pointer to location for returned number of global
   attributes defined for this netCDF dataset. Ignored if NULL.

   \param 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. Ignored
   if NULL.  If there are multiple unlimited dimensions (possible only
   for netCDF-4 files), only a pointer to the first is returned, for
   backward compatibility.  If you want them all, use nc_inq_unlimids().

   \returns ::NC_NOERR No error.

   \returns ::NC_EBADID Invalid ncid passed.

   <h1>Example</h1>

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

   \code
   #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);
   \endcode
*/
int
nc_inq(int ncid, int *ndimsp, int *nvarsp, int *nattsp, int *unlimdimidp)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;
    return ncp->dispatch->inq(ncid,ndimsp,nvarsp,nattsp,unlimdimidp);
}

/**
 * Learn the number of variables in a file or group.
 *
 * @param ncid File and group ID.
 * @param nvarsp Pointer that gets number of variables. Ignored if NULL.
 *
 * @return ::NC_NOERR No error.
 * @return ::NC_EBADID Bad ncid.
 * @author Glenn Davis, Ed Hartnett, Dennis Heimbigner
 */
int
nc_inq_nvars(int ncid, int *nvarsp)
{
    NC* ncp;
    int stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) return stat;
    return ncp->dispatch->inq(ncid, NULL, nvarsp, NULL, NULL);
}

/**\ingroup datasets
   Inquire about a 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 nc_inq_user_type().

   \param ncid The ncid for the group containing the type (ignored for
   atomic types).

   \param 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.).

   \param 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.

   \param size 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.

   \returns ::NC_NOERR No error.

   \returns ::NC_EBADTYPE Bad typeid.

   \returns ::NC_ENOTNC4 Seeking a user-defined type in a netCDF-3 file.

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

   \returns ::NC_EBADGRPID Bad group ID in ncid.

   \returns ::NC_EBADID Type ID not found.

   \returns ::NC_EHDFERR An error was reported by the HDF5 layer.

   <h1>Example</h1>

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

   \code
   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;
   \endcode
*/
int
nc_inq_type(int ncid, nc_type xtype, char *name, size_t *size)
{
    NC* ncp;
    int stat;

    /* Do a quick triage on xtype */
    if(xtype <= NC_NAT) return NC_EBADTYPE;
    /* For compatibility, we need to allow inq about
       atomic types, even if ncid is ill-defined */
    if(xtype <= ATOMICTYPEMAX4) {
        if(name) strncpy(name,NC_atomictypename(xtype),NC_MAX_NAME);
        if(size) *size = NC_atomictypelen(xtype);
        return NC_NOERR;
    }
    /* Apparently asking about a user defined type, so we need
       a valid ncid */
    stat = NC_check_id(ncid, &ncp);
    if(stat != NC_NOERR) /* bad ncid */
        return NC_EBADTYPE;
    /* have good ncid */
    return ncp->dispatch->inq_type(ncid,xtype,name,size);
}

/**
   Check the create mode parameter for sanity.

   Some create flags cannot be used if corresponding library features are
   enabled during the build. This function does a pre-check of the mode
   flag before calling the dispatch layer nc_create functions.

   \param mode The creation mode flag.

   \returns ::NC_NOERR No error.
   \returns ::NC_ENOTBUILT Requested feature not built into library
   \returns ::NC_EINVAL Invalid combination of modes.
   \internal
   \ingroup dispatch
   \author Ed Hartnett
*/
static int
check_create_mode(int mode)
{
    int mode_format;
    int mmap = 0;
    int inmemory = 0;
    int diskless = 0;

    /* This is a clever check to see if more than one format bit is
     * set. */
    mode_format = (mode & NC_NETCDF4) | (mode & NC_64BIT_OFFSET) |
        (mode & NC_CDF5);
    if (mode_format && (mode_format & (mode_format - 1)))
        return NC_EINVAL;

    mmap = ((mode & NC_MMAP) == NC_MMAP);
    inmemory = ((mode & NC_INMEMORY) == NC_INMEMORY);
    diskless = ((mode & NC_DISKLESS) == NC_DISKLESS);

    /* NC_INMEMORY and NC_DISKLESS and NC_MMAP are all mutually exclusive */
    if(diskless && inmemory) return NC_EDISKLESS;
    if(diskless && mmap) return NC_EDISKLESS;
    if(inmemory && mmap) return NC_EINMEMORY;

    /* mmap is not allowed for netcdf-4 */
    if(mmap && (mode & NC_NETCDF4)) return NC_EINVAL;

#ifndef USE_NETCDF4
    /* If the user asks for a netCDF-4 file, and the library was built
     * without netCDF-4, then return an error.*/
    if (mode & NC_NETCDF4)
        return NC_ENOTBUILT;
#endif /* USE_NETCDF4 undefined */

    /* Well I guess there is some sanity in the world after all. */
    return NC_NOERR;
}

/**
 * @internal Create a file, calling the appropriate dispatch create
 * call.
 *
 * For create, we have the following pieces of information to use to
 * determine the dispatch table:
 * - path
 * - cmode
 *
 * @param path0 The file name of the new netCDF dataset.
 * @param cmode The creation mode flag, the same as in nc_create().
 * @param initialsz This parameter sets the initial size of the file
 * at creation time. This only applies to classic
 * files.
 * @param basepe Deprecated parameter from the Cray days.
 * @param chunksizehintp A pointer to the chunk size hint. This only
 * applies to classic files.
 * @param useparallel Non-zero if parallel I/O is to be used on this
 * file.
 * @param parameters Pointer to MPI comm and info.
 * @param ncidp Pointer to location where returned netCDF ID is to be
 * stored.
 *
 * @returns ::NC_NOERR No error.
 * @ingroup dispatch
 * @author Dennis Heimbigner, Ed Hartnett, Ward Fisher
 */
int
NC_create(const char *path0, int cmode, size_t initialsz,
          int basepe, size_t *chunksizehintp, int useparallel,
          void* parameters, int *ncidp)
{
    int stat = NC_NOERR;
    NC* ncp = NULL;
    const NC_Dispatch* dispatcher = NULL;
    char* path = NULL;
    NCmodel model;
    char* newpath = NULL;

    TRACE(nc_create);
    if(path0 == NULL)
        return NC_EINVAL;

    /* Check mode flag for sanity. */
    if ((stat = check_create_mode(cmode)))
        return stat;

    /* Initialize the library. The available dispatch tables
     * will depend on how netCDF was built
     * (with/without netCDF-4, DAP, CDMREMOTE). */
    if(!NC_initialized)
    {
        if ((stat = nc_initialize()))
            return stat;
    }

    {
        /* Skip past any leading whitespace in path */
        const unsigned char* p;
        for(p=(const unsigned char*)path0;*p;p++) {if(*p > ' ') break;}
#ifdef WINPATH
        /* Need to do path conversion */
        path = NCpathcvt((const char*)p);
#else
        path = nulldup((const char*)p);
#endif
    }

    memset(&model,0,sizeof(model));
    if((stat = NC_infermodel(path,&cmode,1,useparallel,NULL,&model,&newpath)))
        goto done;
    if(newpath) {
        nullfree(path);
        path = newpath;
        newpath = NULL;
    }

    assert(model.format != 0 && model.impl != 0);

    /* Now, check for NC_ENOTBUILT cases limited to create (so e.g. HDF4 is not listed) */
#ifndef USE_HDF5
    if (model.impl == NC_FORMATX_NC4)
    {stat = NC_ENOTBUILT; goto done;}
#endif
#ifndef USE_PNETCDF
    if (model.impl == NC_FORMATX_PNETCDF)
    {stat = NC_ENOTBUILT; goto done;}
#endif
#ifndef ENABLE_CDF5
    if (model.impl == NC_FORMATX_NC3 && (cmode & NC_64BIT_DATA))
    {stat = NC_ENOTBUILT; goto done;}
#endif

    /* Figure out what dispatcher to use */
    switch (model.impl) {
#ifdef USE_HDF5
    case NC_FORMATX_NC4:
        dispatcher = HDF5_dispatch_table;
        break;
#endif
#ifdef USE_PNETCDF
    case NC_FORMATX_PNETCDF:
        dispatcher = NCP_dispatch_table;
        break;
#endif
#ifdef USE_NETCDF4
    case NC_FORMATX_UDF0:
        dispatcher = UDF0_dispatch_table;
        break;
    case NC_FORMATX_UDF1:
        dispatcher = UDF1_dispatch_table;
        break;
#endif /* USE_NETCDF4 */
#ifdef ENABLE_NCZARR
    case NC_FORMATX_NCZARR:
        dispatcher = NCZ_dispatch_table;
	break;
#endif
    case NC_FORMATX_NC3:
        dispatcher = NC3_dispatch_table;
        break;
    default:
        return NC_ENOTNC;
    }

    /* Create the NC* instance and insert its dispatcher and model */
    if((stat = new_NC(dispatcher,path,cmode,&ncp))) goto done;

    /* Add to list of known open files and define ext_ncid */
    add_to_NCList(ncp);

    /* Assume create will fill in remaining ncp fields */
    if ((stat = dispatcher->create(ncp->path, cmode, initialsz, basepe, chunksizehintp,
                                   parameters, dispatcher, ncp->ext_ncid))) {
        del_from_NCList(ncp); /* oh well */
        free_NC(ncp);
    } else {
        if(ncidp)*ncidp = ncp->ext_ncid;
    }
done:
    nullfree(path);
    return stat;
}

/**
 * @internal Open a netCDF file (or remote dataset) calling the
 * appropriate dispatch function.
 *
 * For open, we have the following pieces of information to use to
 * determine the dispatch table.
 * - table specified by override
 * - path
 * - omode
 * - the contents of the file (if it exists), basically checking its magic number.
 *
 * @param path0 Path to the file to open.
 * @param omode Open mode.
 * @param basepe Base processing element (ignored).
 * @param chunksizehintp Size hint for classic files.
 * @param useparallel If true use parallel I/O.
 * @param parameters Extra parameters for the open.
 * @param ncidp Pointer that gets ncid.
 *
 * @returns ::NC_NOERR No error.
 * @ingroup dispatch
 * @author Dennis Heimbigner
 */
int
NC_open(const char *path0, int omode, int basepe, size_t *chunksizehintp,
        int useparallel, void* parameters, int *ncidp)
{
    int stat = NC_NOERR;
    NC* ncp = NULL;
    const NC_Dispatch* dispatcher = NULL;
    int inmemory = 0;
    int diskless = 0;
    int mmap = 0;
    char* path = NULL;
    NCmodel model;
    char* newpath = NULL;

    TRACE(nc_open);
    if(!NC_initialized) {
        stat = nc_initialize();
        if(stat) return stat;
    }

    /* Check inputs. */
    if (!path0)
        return NC_EINVAL;

    /* Capture the inmemory related flags */
    mmap = ((omode & NC_MMAP) == NC_MMAP);
    diskless = ((omode & NC_DISKLESS) == NC_DISKLESS);
    inmemory = ((omode & NC_INMEMORY) == NC_INMEMORY);

    /* NC_INMEMORY and NC_DISKLESS and NC_MMAP are all mutually exclusive */
    if(diskless && inmemory) {stat = NC_EDISKLESS; goto done;}
    if(diskless && mmap) {stat = NC_EDISKLESS; goto done;}
    if(inmemory && mmap) {stat = NC_EINMEMORY; goto done;}

    /* mmap is not allowed for netcdf-4 */
    if(mmap && (omode & NC_NETCDF4)) {stat = NC_EINVAL; goto done;}

    /* Attempt to do file path conversion: note that this will do
       nothing if path is a 'file:...' url, so it will need to be
       repeated in protocol code (e.g. libdap2, libdap4, etc).
    */

    {
        /* Skip past any leading whitespace in path */
        const char* p;
        for(p=(const char*)path0;*p;p++) {if(*p < 0 || *p > ' ') break;}
#ifdef WINPATH
        /* Need to do path conversion */
        path = NCpathcvt(p);
#else
        path = nulldup(p);
#endif
    }

    memset(&model,0,sizeof(model));
    /* Infer model implementation and format, possibly by reading the file */
    if((stat = NC_infermodel(path,&omode,0,useparallel,parameters,&model,&newpath)))
        goto done;
    if(newpath) {
        nullfree(path);
        path = newpath;
	newpath = NULL;
    }

    /* Still no implementation, give up */
    if(model.impl == 0) {
#ifdef DEBUG
        fprintf(stderr,"implementation == 0\n");
#endif
        {stat = NC_ENOTNC; goto done;}
    }

    /* Suppress unsupported formats */
    /* (should be more compact, table-driven, way to do this) */
    {
	int hdf5built = 0;
	int hdf4built = 0;
	int cdf5built = 0;
	int udf0built = 0;
	int udf1built = 0;
	int nczarrbuilt = 0;
#ifdef USE_NETCDF4
        hdf5built = 1;
#ifdef USE_HDF4
        hdf4built = 1;
#endif
#endif
#ifdef ENABLE_CDF5
        cdf5built = 1;
#endif
#ifdef ENABLE_NCZARR
	nczarrbuilt = 1;
#endif
        if(UDF0_dispatch_table != NULL)
            udf0built = 1;
        if(UDF1_dispatch_table != NULL)
            udf1built = 1;

        if(!hdf5built && model.impl == NC_FORMATX_NC4)
        {stat = NC_ENOTBUILT; goto done;}
        if(!hdf4built && model.impl == NC_FORMATX_NC_HDF4)
        {stat = NC_ENOTBUILT; goto done;}
        if(!cdf5built && model.impl == NC_FORMATX_NC3 && model.format == NC_FORMAT_CDF5)
        {stat = NC_ENOTBUILT; goto done;}
	if(!nczarrbuilt && model.impl == NC_FORMATX_NCZARR)
        {stat = NC_ENOTBUILT; goto done;}
        if(!udf0built && model.impl == NC_FORMATX_UDF0)
        {stat = NC_ENOTBUILT; goto done;}
        if(!udf1built && model.impl == NC_FORMATX_UDF1)
        {stat = NC_ENOTBUILT; goto done;}
    }
    /* Figure out what dispatcher to use */
    if (!dispatcher) {
        switch (model.impl) {
#ifdef ENABLE_DAP
        case NC_FORMATX_DAP2:
            dispatcher = NCD2_dispatch_table;
            break;
#endif
#ifdef ENABLE_DAP4
        case NC_FORMATX_DAP4:
            dispatcher = NCD4_dispatch_table;
            break;
#endif
#ifdef ENABLE_NCZARR
	case NC_FORMATX_NCZARR:
	    dispatcher = NCZ_dispatch_table;
	    break;
#endif
#ifdef USE_PNETCDF
        case NC_FORMATX_PNETCDF:
            dispatcher = NCP_dispatch_table;
            break;
#endif
#ifdef USE_HDF5
        case NC_FORMATX_NC4:
            dispatcher = HDF5_dispatch_table;
            break;
#endif
#ifdef USE_HDF4
        case NC_FORMATX_NC_HDF4:
            dispatcher = HDF4_dispatch_table;
            break;
#endif
#ifdef USE_NETCDF4
        case NC_FORMATX_UDF0:
            dispatcher = UDF0_dispatch_table;
            break;
        case NC_FORMATX_UDF1:
            dispatcher = UDF1_dispatch_table;
            break;
#endif /* USE_NETCDF4 */
        case NC_FORMATX_NC3:
            dispatcher = NC3_dispatch_table;
            break;
        default:
            stat = NC_ENOTNC;
	    goto done;
        }
    }


    /* If we can't figure out what dispatch table to use, give up. */
    if (!dispatcher) {stat = NC_ENOTNC; goto done;}

    /* Create the NC* instance and insert its dispatcher */
    if((stat = new_NC(dispatcher,path,omode,&ncp))) goto done;

    /* Add to list of known open files. This assigns an ext_ncid. */
    add_to_NCList(ncp);

    /* Assume open will fill in remaining ncp fields */
    stat = dispatcher->open(ncp->path, omode, basepe, chunksizehintp,
                            parameters, dispatcher, ncp->ext_ncid);
    if(stat == NC_NOERR) {
        if(ncidp) *ncidp = ncp->ext_ncid;
    } else {
        del_from_NCList(ncp);
        free_NC(ncp);
    }

done:
    nullfree(path);
    nullfree(newpath);
    return stat;
}

/*Provide an internal function for generating pseudo file descriptors
  for systems that are not file based (e.g. dap, memio).
*/

/** @internal Static counter for pseudo file descriptors (incremented) */
static int pseudofd = 0;

/**
 * @internal Create a pseudo file descriptor that does not
 * overlap real file descriptors
 *
 * @return pseudo file number
 * @author Dennis Heimbigner
 */
int
nc__pseudofd(void)
{
    if(pseudofd == 0)  {
        int maxfd = 32767; /* default */
#ifdef HAVE_GETRLIMIT
        struct rlimit rl;
        if(getrlimit(RLIMIT_NOFILE,&rl) == 0) {
            if(rl.rlim_max != RLIM_INFINITY)
                maxfd = (int)rl.rlim_max;
            if(rl.rlim_cur != RLIM_INFINITY)
                maxfd = (int)rl.rlim_cur;
        }
        pseudofd = maxfd+1;
#endif
    }
    return pseudofd++;
}