netcdf-c/libdispatch/dvarinq.c

/* Copyright 2018 University Corporation for Atmospheric
   Research/Unidata. See COPYRIGHT file for more info. */
/*! \file
Functions for inquiring about variables.

*/

#include "config.h"
#include "netcdf.h"
#include "netcdf_filter.h"
#include "ncdispatch.h"
#include "nc4internal.h"
#ifdef USE_HDF5
#include <hdf5.h>
#endif /* USE_HDF5 */

/** \name Learning about Variables

Functions to learn about the variables in a file. */
/*! \{ */ /* All these functions are part of this named group... */

/**
\ingroup variables
Find the ID of a variable, from the name.

The function nc_inq_varid returns the ID of a netCDF variable, given
its name.

\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 name Name of the variable.

\param varidp Pointer to location for returned variable ID.  \ref
ignored_if_null.

\returns ::NC_NOERR No error.
\returns ::NC_EBADID Bad ncid.
\returns ::NC_ENOTVAR Invalid variable ID.

\section nc_inq_varid_example4 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:

\code
     #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);
\endcode
 */
int
nc_inq_varid(int ncid, const char *name, int *varidp)
{
   NC* ncp;
   int stat = NC_check_id(ncid, &ncp);
   if(stat != NC_NOERR) return stat;
   return ncp->dispatch->inq_varid(ncid, name, varidp);
}

/**
\ingroup variables
Learn about a 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

\param name Returned \ref object_name of variable. \ref
ignored_if_null.

\param xtypep Pointer where typeid will be stored. \ref ignored_if_null.

\param ndimsp Pointer where number of dimensions will be
stored. \ref ignored_if_null.

\param dimidsp Pointer where array of dimension IDs will be
stored. \ref ignored_if_null.

\param nattsp Pointer where number of attributes will be
stored. \ref ignored_if_null.

\returns ::NC_NOERR No error.
\returns ::NC_EBADID Bad ncid.
\returns ::NC_ENOTVAR Invalid variable ID.

\section nc_inq_var_example5 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:

\code
     #include <netcdf.h>
        ...
     int  status
     int  ncid;
     int  rh_id;
     nc_type rh_type;
     int rh_ndims;
     int  rh_dimids[NC_MAX_VAR_DIMS];
     int rh_natts
        ...
     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_var (ncid, rh_id, 0, &rh_type, &rh_ndims, rh_dimids,
                          &rh_natts);
     if (status != NC_NOERR) handle_error(status);
\endcode

 */
int
nc_inq_var(int ncid, int varid, char *name, nc_type *xtypep,
	   int *ndimsp, int *dimidsp, int *nattsp)
{
   NC* ncp;
   int stat = NC_check_id(ncid, &ncp);
   if(stat != NC_NOERR) return stat;
   TRACE(nc_inq_var);
   return ncp->dispatch->inq_var_all(ncid, varid, name, xtypep, ndimsp,
				     dimidsp, nattsp, NULL, NULL, NULL,
				     NULL, NULL, NULL, NULL, NULL, NULL,
				     NULL,NULL,NULL);
}

/**
\ingroup variables
Learn the name of a 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

\param name Returned variable name. The caller must allocate space for
the returned name. The maximum length is ::NC_MAX_NAME. Ignored if
NULL.

\returns ::NC_NOERR No error.
\returns ::NC_EBADID Bad ncid.
\returns ::NC_ENOTVAR Invalid variable ID.
 */
int
nc_inq_varname(int ncid, int varid, char *name)
{
   return nc_inq_var(ncid, varid, name, NULL, NULL,
		     NULL, NULL);
}

/** Learn the type of a variable.
\ingroup variables

\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

\param typep Pointer where typeid will be stored. \ref ignored_if_null.

\returns ::NC_NOERR No error.
\returns ::NC_EBADID Bad ncid.
\returns ::NC_ENOTVAR Invalid variable ID.
 */
int
nc_inq_vartype(int ncid, int varid, nc_type *typep)
{
   return nc_inq_var(ncid, varid, NULL, typep, NULL,
		     NULL, NULL);
}

/**
Learn how many dimensions are associated with a variable.
\ingroup variables

\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

\param ndimsp Pointer where number of dimensions will be
stored. \ref ignored_if_null.

\returns ::NC_NOERR No error.
\returns ::NC_EBADID Bad ncid.
\returns ::NC_ENOTVAR Invalid variable ID.
 */
int
nc_inq_varndims(int ncid, int varid, int *ndimsp)
{
   return nc_inq_var(ncid, varid, NULL, NULL, ndimsp, NULL, NULL);
}

/**
Learn the dimension IDs associated with a variable.
\ingroup variables

\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

\param dimidsp Pointer where array of dimension IDs will be
stored. \ref ignored_if_null.

\returns ::NC_NOERR No error.
\returns ::NC_EBADID Bad ncid.
\returns ::NC_ENOTVAR Invalid variable ID.
 */
int
nc_inq_vardimid(int ncid, int varid, int *dimidsp)
{
   return nc_inq_var(ncid, varid, NULL, NULL, NULL,
		     dimidsp, NULL);
}

/**
Learn how many attributes are associated with a variable.
\ingroup variables

\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

\param nattsp Pointer where number of attributes will be
stored. \ref ignored_if_null.

\returns ::NC_NOERR No error.
\returns ::NC_EBADID Bad ncid.
\returns ::NC_ENOTVAR Invalid variable ID.
 */
int
nc_inq_varnatts(int ncid, int varid, int *nattsp)
{
   if (varid == NC_GLOBAL)
      return nc_inq_natts(ncid,nattsp);
   /*else*/
   return nc_inq_var(ncid, varid, NULL, NULL, NULL, NULL,
		     nattsp);
}

/** 
\ingroup variables 

Learn the shuffle and deflate settings for a variable.

Deflation is compression with the zlib library. Shuffle re-orders the
data bytes to provide better compression (see nc_def_var_deflate()).

Deflation is only available for HDF5 files. For classic and other
files, this function will return setting that indicate that deflation
is not in use, and that the shuffle filter is not in use. That is:
shuffle off, deflate off, and a deflate level of 0.

\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

\param shufflep A 1 will be written here if the shuffle filter is
turned on for this variable, and a 0 otherwise. \ref ignored_if_null.

\param 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. \ref ignored_if_null.

\param deflate_levelp If the deflate filter is in use for this
variable, the deflate_level will be written here. If deflate is not in
use, and deflate_levelp is provided, it will get a zero. (This
behavior is expected by the Fortran APIs). \ref ignored_if_null.

\returns ::NC_NOERR No error.
\returns ::NC_EBADID Bad ncid.
\returns ::NC_ENOTVAR Invalid variable ID.
\author Ed Hartnett, Dennis Heimbigner
*/
int
nc_inq_var_deflate(int ncid, int varid, int *shufflep, int *deflatep, int *deflate_levelp)
{
   NC* ncp;
   size_t nparams;
   unsigned int params[4];
   int deflating = 0;
   int stat;
   
   stat = NC_check_id(ncid,&ncp);
   if(stat != NC_NOERR) return stat;
   TRACE(nc_inq_var_deflate);

   /* Verify id and  nparams */
   stat = nc_inq_var_filter_info(ncid,varid,H5Z_FILTER_DEFLATE,&nparams,params);
   switch (stat) {
   case NC_ENOFILTER: deflating = 0; stat = NC_NOERR; break;
   case NC_NOERR: deflating = 1; break;
   case NC_ENOTNC4:
       /* As a special case, to support behavior already coded into user
	* applications, handle classic format files by reporting no
	* deflation. */
       if (shufflep)
	   *shufflep = 0;
       if (deflatep)
	   *deflatep = 0;
       if (deflate_levelp)
	   *deflate_levelp = 0;
       return NC_NOERR;
       break;
   default: return stat;
   }
   if(deflatep) *deflatep = deflating;
   if(deflating) {
        if(nparams != 1)
	    return NC_EFILTER; /* bad # params */
	/* Param[0] should be level */
	if(deflate_levelp) *deflate_levelp = (int)params[0];
   } else if (deflate_levelp)
       *deflate_levelp = 0;
   /* also get the shuffle state */
   if(!shufflep)
       return NC_NOERR;
   return ncp->dispatch->inq_var_all(
      ncid, varid,
      NULL, /*name*/
      NULL, /*xtypep*/
      NULL, /*ndimsp*/
      NULL, /*dimidsp*/
      NULL, /*nattsp*/
      shufflep, /*shufflep*/
      NULL, /*deflatep*/
      NULL, /*deflatelevelp*/
      NULL, /*fletcher32p*/
      NULL, /*contiguousp*/
      NULL, /*chunksizep*/
      NULL, /*nofillp*/
      NULL, /*fillvaluep*/
      NULL, /*endianp*/
      NULL, NULL, NULL
      );
}

/** \ingroup variables
Learn the checksum settings for a variable.

This is a wrapper for nc_inq_var_all().

\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

\param fletcher32p Will be set to ::NC_FLETCHER32 if the fletcher32
checksum filter is turned on for this variable, and ::NC_NOCHECKSUM if
it is not. \ref ignored_if_null.

\returns ::NC_NOERR No error.
\returns ::NC_EBADID Bad ncid.
\returns ::NC_ENOTNC4 Not a netCDF-4 file.
\returns ::NC_ENOTVAR Invalid variable ID.
*/
int
nc_inq_var_fletcher32(int ncid, int varid, int *fletcher32p)
{
   NC* ncp;
   int stat = NC_check_id(ncid,&ncp);
   if(stat != NC_NOERR) return stat;
   TRACE(nc_inq_var_fletcher32);
   return ncp->dispatch->inq_var_all(
      ncid, varid,
      NULL, /*name*/
      NULL, /*xtypep*/
      NULL, /*ndimsp*/
      NULL, /*dimidsp*/
      NULL, /*nattsp*/
      NULL, /*shufflep*/
      NULL, /*deflatep*/
      NULL, /*deflatelevelp*/
      fletcher32p, /*fletcher32p*/
      NULL, /*contiguousp*/
      NULL, /*chunksizep*/
      NULL, /*nofillp*/
      NULL, /*fillvaluep*/
      NULL, /*endianp*/
      NULL, NULL, NULL
      );
}

/**
 * @ingroup variables
 *
 * Get the storage and (for chunked variables) the chunksizes of a
 * variable. See nc_def_var_chunking() for explanation of storage.
 *
 * @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
 * @param storagep Address of returned storage property, returned as
 * ::NC_CONTIGUOUS if this variable uses contiguous storage,
 * ::NC_CHUNKED if it uses chunked storage, or ::NC_COMPACT for
 * compact storage. \ref ignored_if_null.
 * @param chunksizesp The chunksizes will be copied here. \ref
 * ignored_if_null.
 *
 * @return ::NC_NOERR No error.
 * @return ::NC_EBADID Bad ncid.
 * @return ::NC_ENOTNC4 Not a netCDF-4 file.
 * @return ::NC_ENOTVAR Invalid variable ID.
 *
 * @author Ed Hartnett
 *
 * @section nc_inq_var_chunking_example Example
 *
 * @code
        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;


           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;


           if (nc_inq_var_chunking(ncid, 0, &storage_in, chunksize_in)) ERR;
           if (storage_in != NC_CONTIGUOUS) ERR;
@endcode
*
*/
int
nc_inq_var_chunking(int ncid, int varid, int *storagep, size_t *chunksizesp)
{
   NC *ncp;
   int stat = NC_check_id(ncid, &ncp);
   if(stat != NC_NOERR) return stat;
   TRACE(nc_inq_var_chunking);
   return ncp->dispatch->inq_var_all(ncid, varid, NULL, NULL, NULL, NULL,
				     NULL, NULL, NULL, NULL, NULL, storagep,
				     chunksizesp, NULL, NULL, NULL,
                                     NULL, NULL, NULL);
}

/** \ingroup variables
Learn the fill mode of a variable.

The fill mode of a variable is set by nc_def_var_fill().

This is a wrapper for nc_inq_var_all().

\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

\param no_fill Pointer to an integer which will get a 1 if no_fill
mode is set for this variable. \ref ignored_if_null.

\param fill_valuep A pointer which will get the fill value for this
variable. \ref ignored_if_null.

\returns ::NC_NOERR No error.
\returns ::NC_EBADID Bad ncid.
\returns ::NC_ENOTVAR Invalid variable ID.
*/
int
nc_inq_var_fill(int ncid, int varid, int *no_fill, void *fill_valuep)
{
   NC* ncp;
   int stat = NC_check_id(ncid,&ncp);

   if(stat != NC_NOERR) return stat;
   TRACE(nc_inq_var_fill);

   return ncp->dispatch->inq_var_all(
      ncid,varid,
      NULL, /*name*/
      NULL, /*xtypep*/
      NULL, /*ndimsp*/
      NULL, /*dimidsp*/
      NULL, /*nattsp*/
      NULL, /*shufflep*/
      NULL, /*deflatep*/
      NULL, /*deflatelevelp*/
      NULL, /*fletcher32p*/
      NULL, /*contiguousp*/
      NULL, /*chunksizep*/
      no_fill, /*nofillp*/
      fill_valuep, /*fillvaluep*/
      NULL, /*endianp*/
      NULL, NULL, NULL
      );
}

/** @ingroup variables
 * Learn whether BitGroom quantization is on for a variable, and, if so,
 * the NSD setting.
 *
 * @param ncid File ID.
 * @param varid Variable ID. Must not be NC_GLOBAL.
 * @param quantize_modep Pointer that gets a 0 if BitGroom is not in
 * use for this var, and a 1 if it is. Ignored if NULL.
 * @param nsdp Pointer that gets the NSD setting (from 1 to 15), if
 * BitGroom is in use. Ignored if NULL.
 *
 * @return 0 for success, error code otherwise.
 * @author Charlie Zender, Ed Hartnett
*/
int
nc_inq_var_quantize(int ncid, int varid, int *quantize_modep, int *nsdp)
{
   NC* ncp;
   int stat = NC_check_id(ncid,&ncp);

   if(stat != NC_NOERR) return stat;
   TRACE(nc_inq_var_quantize);
   
   /* Using NC_GLOBAL is illegal. */
   if (varid == NC_GLOBAL) return NC_EGLOBAL;

   return ncp->dispatch->inq_var_quantize(ncid, varid,
					  quantize_modep, nsdp);
}

/** \ingroup variables
Find the endianness of a variable.

This is a wrapper for nc_inq_var_all().

\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

\param endianp Storage which will get ::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.

\returns ::NC_NOERR No error.
\returns ::NC_ENOTNC4 Not a netCDF-4 file.
\returns ::NC_EBADID Bad ncid.
\returns ::NC_ENOTVAR Invalid variable ID.
*/
int
nc_inq_var_endian(int ncid, int varid, int *endianp)
{
   NC* ncp;
   int stat = NC_check_id(ncid,&ncp);
   if(stat != NC_NOERR) return stat;
   TRACE(nc_inq_var_endian);
   return ncp->dispatch->inq_var_all(
      ncid, varid,
      NULL, /*name*/
      NULL, /*xtypep*/
      NULL, /*ndimsp*/
      NULL, /*dimidsp*/
      NULL, /*nattsp*/
      NULL, /*shufflep*/
      NULL, /*deflatep*/
      NULL, /*deflatelevelp*/
      NULL, /*fletcher32p*/
      NULL, /*contiguousp*/
      NULL, /*chunksizep*/
      NULL, /*nofillp*/
      NULL, /*fillvaluep*/
      endianp, /*endianp*/
      NULL, NULL, NULL);
}

/**
Return number and list of unlimited dimensions.

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.

\param ncid NetCDF file and group ID, from a previous call to nc_open(),
nc_create(), nc_def_grp(), etc.

\param nunlimdimsp A pointer to an int which will get the number of
visible unlimited dimensions. Ignored if NULL.

\param 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.

\section nc_inq_unlimdims_example Example

Here is an example from nc_test4/tst_dims.c. In this example we create
a file with two unlimited dimensions, and then call nc_inq_unlimdims()
to check that there are 2 unlimited dimensions, and that they have
dimids 0 and 1.

\code
     #include <netcdf.h>
        ...
#define ROMULUS "Romulus"
#define REMUS "Remus"
#define DIMS2 2
   printf("*** Testing file with two unlimited dimensions...");
   {
      int ncid, dimid[DIMS2];
      int unlimdimid_in[DIMS2];
      int nunlimdims_in;

      if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
      if (nc_def_dim(ncid, REMUS, NC_UNLIMITED, &dimid[0])) ERR;
      if (nc_def_dim(ncid, ROMULUS, NC_UNLIMITED, &dimid[1])) ERR;

      ...
      if (nc_inq_unlimdims(ncid, &nunlimdims_in, unlimdimid_in)) ERR;
      if (nunlimdims_in != 2 || unlimdimid_in[0] != 0 || unlimdimid_in[1] != 1) ERR;
\endcode

This function will return one of the following values.

\returns ::NC_NOERR No error.
\returns ::NC_EBADID Bad group id.
\returns ::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. (see nc_open).
\returns ::NC_ESTRICTNC3 This file was created with the strict
netcdf-3 flag, therefore netcdf-4 operations are not allowed. (see
nc_open).
\returns ::NC_EHDFERR An error was reported by the HDF5 layer.
\author Ed Hartnett, Dennis Heimbigner
 */
int
nc_inq_unlimdims(int ncid, int *nunlimdimsp, int *unlimdimidsp)
{
#ifndef USE_NETCDF4
    return NC_ENOTNC4;
#else
    NC* ncp;
    int stat = NC_check_id(ncid,&ncp);
    if(stat != NC_NOERR) return stat;
    TRACE(nc_inq_unlimdims);
    return ncp->dispatch->inq_unlimdims(ncid, nunlimdimsp,
					unlimdimidsp);
#endif
}

/**
\ingroup variables
Learn the szip settings of a variable.

This function returns the szip settings for a variable. To turn on
szip compression, use nc_def_var_szip(). Szip compression is only
available for netCDF/HDF5 files, and only if HDF5 was built with szip
support. 

If a variable is not using szip, or if this function is called on a
file that is not a HDF5 file, then a zero will be passed back for both
options_maskp and pixels_per_blockp.

For more information on HDF5 and szip see
https://support.hdfgroup.org/HDF5/doc/RM/RM_H5P.html#Property-SetSzip
and https://support.hdfgroup.org/doc_resource/SZIP/index.html.

The nc_def_var_filter function may also be used to set szip
compression.

\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

\param options_maskp The szip options mask will be copied to this
pointer. Note that the HDF5 layer adds to the options_mask, so this
value may be different from the value used when setting szip
compression, however the bit set when setting szip compression will
still be set in the options_maskp and can be checked for. If zero is
returned, szip is not in use for this variable.\ref ignored_if_null.

\param pixels_per_blockp The szip pixels per block will be copied
here. The HDF5 layer may change this value, so this may not match the
value passed in when setting szip compression. If zero is returned,
szip is not in use for this variable. \ref ignored_if_null.

\returns ::NC_NOERR No error.
\returns ::NC_EBADID Bad ncid.
\returns ::NC_ENOTVAR Invalid variable ID.
\returns ::NC_EFILTER Filter error.

\author Ed Hartnett, Dennis Heimbigner
*/
int
nc_inq_var_szip(int ncid, int varid, int *options_maskp, int *pixels_per_blockp)
{
   NC* ncp;
   size_t nparams;
   unsigned int params[4];

   int stat = NC_check_id(ncid,&ncp);
   if(stat != NC_NOERR) return stat;
   TRACE(nc_inq_var_szip);

   /* Verify id and nparams */
   stat = nc_inq_var_filter_info(ncid,varid,H5Z_FILTER_SZIP,&nparams,params);
   switch (stat) {
   case NC_NOERR:
        if(nparams < 2)
	    return NC_EFILTER; /* bad # params */
	if(nparams > 2)
	    nparams = 2; /* for compatibility, only return 2 params */
	break;
   case NC_ENOFILTER:
   case NC_ENOTNC4:
       /* If the szip filter is not in use, or if this is not a HDF5
	* file, return 0 for both parameters. */
       params[0] = 0;
       params[1] = 0;
       stat = NC_NOERR;
       break;	   
   default:
   	return stat;
   }

   /* Param[0] should be options_mask
      Param[1] should be pixels_per_block */
   if(options_maskp) *options_maskp = (int)params[0];
   if(pixels_per_blockp) *pixels_per_blockp = (int)params[1];
   return stat;
}

/*! \} */  /* End of named group ...*/