• The zlib library may be used to deflate variables.

  /* Set compression settings for a variable. Lower is faster, higher is
   * better. Must be called after nc_def_var and before nc_enddef. */
  EXTERNL int
  nc_def_var_deflate(int ncid, int varid, int shuffle, int deflate, 
     int deflate_level);
  
  /* Find out compression settings of a var. */
  EXTERNL int
  nc_inq_var_deflate(int ncid, int varid, int *shufflep, 
     int *deflatep, int *deflate_levelp);
  
  

• From libsrc4/tst_vars.c, the following code demonstrates the use of per variable compression. Use the nc_def_var_deflate function, after a var has been defined, before leaving define mode.

        if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
        if (nc_def_dim(ncid, DIM1_NAME, DIM1_LEN, &dimids[0])) ERR;
        if (nc_def_dim(ncid, DIM2_NAME, DIM2_LEN, &dimids[1])) ERR;
        if (nc_def_dim(ncid, DIM3_NAME, DIM3_LEN, &dimids[2])) ERR;
        if (nc_def_var(ncid, VAR_BYTE_NAME, NC_BYTE, 2, dimids, &byte_varid)) ERR;
        if (nc_def_var_deflate(ncid, byte_varid, 0, 1, DEFLATE_LEVEL_4)) ERR;
        if (nc_def_var(ncid, VAR_CHAR_NAME, NC_CHAR, 3, dimids, &char_varid)) ERR;
        if (nc_def_var_deflate(ncid, byte_varid, 0, 1, DEFLATE_LEVEL_4)) ERR;
  
        if (nc_put_var_schar(ncid, byte_varid, (signed char *)byte_out)) ERR;
        if (nc_put_var_text(ncid, char_varid, (char *)char_out)) ERR;
   ...
        /* Open the file and check data. */
        if (nc_open(FILE_NAME, 0, &ncid)) ERR;
        if (nc_get_var_schar(ncid, byte_varid, (signed char *)byte_in)) ERR;   
        for (i = 0; i < DIM1_LEN; i++)
  	 for (j = 0; j < DIM2_LEN; j++)
  	    if (byte_in[i][j] != byte_out[i][j]) ERR;
  
  

2007 Unidata NetCDF Workshop for Developers and Data Providers > Using NetCDF-4 Features, Part 1