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5.1.1.2 simple_nc4_rd.c
     /* This is part of the netCDF package. Copyright 2006 University
        Corporation for Atmospheric Research/Unidata.  See COPYRIGHT file
        for conditions of use.
     
        This is a very simple example which demonstrates some of the
        new features of netCDF-4.0.
     
        This example reads a simple file created by simple_nc4_wr.c. This
        is intended to illustrate the use of the netCDF-4 C API.
     
        This program is part of the netCDF tutorial:
        http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-tutorial.html
     
        Full documentation of the netCDF C API can be found at:
        http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-c.html
     
        $Id: simple_nc4_rd.c,v 1.3 2008/06/19 13:29:18 ed Exp $
     */
     #include <stdlib.h>
     #include <stdio.h>
     #include <netcdf.h>
     
     /* This is the name of the data file we will read. */
     #define FILE_NAME "simple_nc4.nc"
     
     /* We are reading 2D data, a 6 x 12 grid. */
     #define NX 6
     #define NY 12
     
     /* Handle errors by printing an error message and exiting with a
      * non-zero status. */
     #define ERRCODE 2
     #define ERR(e) {printf("Error: %s\n", nc_strerror(e)); exit(ERRCODE);}
     
     int
     main()
     {
        /* There will be netCDF IDs for the file, each group, and each
         * variable. */
        int ncid, varid1, varid2, grp1id, grp2id;
     
        unsigned long long data_in[NX][NY];
     
        /* Loop indexes, and error handling. */
        int x, y, retval;
     
        /* The following struct is written as a compound type. */
        struct s1
        {
              int i1;
              int i2;
        };
        struct s1 compound_data[NX][NY];
     
        /* Open the file. NC_NOWRITE tells netCDF we want read-only access
         * to the file.*/
        if ((retval = nc_open(FILE_NAME, NC_NOWRITE, &ncid)))
           ERR(retval);
     
        /* Get the group ids of our two groups. */
        if ((retval = nc_inq_ncid(ncid, "grp1", &grp1id)))
           ERR(retval);
        if ((retval = nc_inq_ncid(ncid, "grp2", &grp2id)))
           ERR(retval);
     
        /* Get the varid of the uint64 data variable, based on its name, in
         * grp1. */
        if ((retval = nc_inq_varid(grp1id, "data", &varid1)))
           ERR(retval);
     
        /* Read the data. */
        if ((retval = nc_get_var_ulonglong(grp1id, varid1, &data_in[0][0])))
           ERR(retval);
     
        /* Get the varid of the compound data variable, based on its name,
         * in grp2. */
        if ((retval = nc_inq_varid(grp2id, "data", &varid2)))
           ERR(retval);
     
        /* Read the data. */
        if ((retval = nc_get_var(grp2id, varid2, &compound_data[0][0])))
           ERR(retval);
     
        /* Check the data. */
        for (x = 0; x < NX; x++)
           for (y = 0; y < NY; y++)
           {
              if (data_in[x][y] != x * NY + y ||
                  compound_data[x][y].i1 != 42 ||
                  compound_data[x][y].i2 != -42)
                 return ERRCODE;
           }
     
        /* Close the file, freeing all resources. */
        if ((retval = nc_close(ncid)))
           ERR(retval);
     
        printf("*** SUCCESS reading example file %s!\n", FILE_NAME);
        return 0;
     }