simple_nc4_wr.c

/* Copyright 2019 University Corporation for Atmospheric
   Research/Unidata.  See COPYRIGHT file for conditions of use. */
#include <stdlib.h>
#include <stdio.h>
#include <netcdf.h>
 
/* This is the name of the data file we will create. */
#define FILE_NAME "simple_nc4.nc"
 
/* We are writing 2D data, a 6 x 12 grid. */
#define NDIMS 2
#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()
{
   /* When we create netCDF variables, groups, dimensions, or types,
    * we get back an ID for each one. */
   int ncid, x_dimid, y_dimid, varid1, varid2, grp1id, grp2id, typeid;
   int dimids[NDIMS];
 
   /* This is the data array we will write. It will be filled with a
    * progression of numbers for this example. */
   unsigned long long data_out[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];
 
   /* Create some pretend data. */
   for (x = 0; x < NX; x++)
      for (y = 0; y < NY; y++)
      {
         data_out[x][y] = x * NY + y;
         compound_data[x][y].i1 = 42;
         compound_data[x][y].i2 = -42;
      }
 
   /* Create the file. The NC_NETCDF4 flag tells netCDF to
    * create a netCDF-4/HDF5 file.*/
   if ((retval = nc_create(FILE_NAME, NC_NETCDF4|NC_CLOBBER, &ncid)))
      ERR(retval);
 
   /* Define the dimensions in the root group. Dimensions are visible
    * in all subgroups. */
   if ((retval = nc_def_dim(ncid, "x", NX, &x_dimid)))
      ERR(retval);
   if ((retval = nc_def_dim(ncid, "y", NY, &y_dimid)))
      ERR(retval);
 
   /* The dimids passes the IDs of the dimensions of the variable. */
   dimids[0] = x_dimid;
   dimids[1] = y_dimid;
 
   /* Define two groups, "grp1" and "grp2." */
   if ((retval = nc_def_grp(ncid, "grp1", &grp1id)))
      ERR (retval);
   if ((retval = nc_def_grp(ncid, "grp2", &grp2id)))
      ERR (retval);
 
   /* Define an unsigned 64bit integer variable in grp1, using dimensions
    * in the root group. */
   if ((retval = nc_def_var(grp1id, "data", NC_UINT64, NDIMS,
                            dimids, &varid1)))
      ERR(retval);
 
   /* Write unsigned long long data to the file. For netCDF-4 files,
    * nc_enddef will be called automatically. */
   if ((retval = nc_put_var_ulonglong(grp1id, varid1, &data_out[0][0])))
      ERR(retval);
 
   /* Create a compound type. This will cause nc_reddef to be called. */
   if (nc_def_compound(grp2id, sizeof(struct s1), "sample_compound_type",
                       &typeid))
      ERR(retval);
   if (nc_insert_compound(grp2id, typeid, "i1",
                          offsetof(struct s1, i1), NC_INT))
      ERR(retval);
   if (nc_insert_compound(grp2id, typeid, "i2",
                          offsetof(struct s1, i2), NC_INT))
      ERR(retval);
 
   /* Define a compound type variable in grp2, using dimensions
    * in the root group. */
   if ((retval = nc_def_var(grp2id, "data", typeid, NDIMS,
                            dimids, &varid2)))
      ERR(retval);
 
   /* Write the array of struct to the file. This will cause nc_endef
    * to be called. */
   if ((retval = nc_put_var(grp2id, varid2, &compound_data[0][0])))
      ERR(retval);
 
   /* Close the file. */
   if ((retval = nc_close(ncid)))
      ERR(retval);
 
   printf("*** SUCCESS writing example file simple_nc4.nc!\n");
   return 0;
}