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GRIB-API support is being discontinued at the end of 2018. Please consider upgrading to ecCodes


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/*
 * C Implementation: multi_write
 *
 * Description: How to encode grib edition 2 messages containing multiple fields. 
 *
 */
#include <stdio.h>
#include <stdlib.h>

#include "grib_api.h"

void usage(char* prog) {
  printf("usage: %s in.grib out.grib\n",prog);
  exit(1);
}

int main(int argc, char** argv)
{
  int err = 0;
  FILE* in = NULL;
  FILE* of = NULL;
  long step;
  char* filename=NULL;
  char* ofilename=NULL;
  grib_handle *h = NULL;
  grib_multi_handle *mh=NULL;
  const int start_section = 4; /* Grib2 Product Definition Section */

  if (argc < 3) usage(argv[0]);
  filename=argv[1];
  ofilename=argv[2];

  /* open input file */
  in = fopen(filename,"r");
  if(!in) {
    printf("ERROR: unable to open file %s\n",filename);
    return 1;
  }

  /* new grib handle from input file */
  h = grib_handle_new_from_file(0,in,&err);  
  GRIB_CHECK(err,0);
  /* create a new empty multi field handle */
  mh=grib_multi_handle_new(0);
  if (!mh) {
    printf("unable to create multi field handle\n");
    exit(1);
  }

  for (step=12;step<=120;step+=12) {
    /* set step */
    grib_set_long(h,"step",step);
    /* append h to mh repeating the sections preceding section 4 */
    grib_multi_handle_append(h, start_section, mh);
  }

  /* open output file */
  of=fopen(ofilename,"w");
  if(!of) {
    printf("ERROR: unable to open file %s\n",ofilename);
    exit(1);
  }

  /* write multi fields handle to output file */
  grib_multi_handle_write(mh,of);
  fclose(of);

  /* release memory */
  grib_handle_delete(h);
  grib_multi_handle_delete(mh);

  fclose(in);
  return 0;
}
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