eccodes/examples/C/grib_print_data.c

/*
 * (C) Copyright 2005- ECMWF.
 *
 * This software is licensed under the terms of the Apache Licence Version 2.0
 * which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
 *
 * In applying this licence, ECMWF does not waive the privileges and immunities granted to it by
 * virtue of its status as an intergovernmental organisation nor does it submit to any jurisdiction.
 */

/*
 * C Implementation: grib_print_data
 *
 * Description: prints all the data contained in a GRIB file
 *
 */
#include <stdio.h>
#include <stdlib.h>

#include "eccodes.h"

static void usage(const char* prog)
{
    printf("usage: %s filename\n", prog);
    exit(1);
}

int main(int argc, char** argv)
{
    int err        = 0, i;
    double* values = NULL;
    double max, min, average;
    size_t values_len = 0;

    FILE* in = NULL;
    char* filename;
    codes_handle* h = NULL;

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

    in = fopen(filename, "rb");
    if (!in) {
        fprintf(stderr, "Error: unable to open file %s\n", filename);
        return 1;
    }

    /* create new handle from a message in a file*/
    h = codes_handle_new_from_file(0, in, PRODUCT_GRIB, &err);
    if (h == NULL) {
        fprintf(stderr, "Error: unable to create handle from file %s\n", filename);
        return 1;
    }

    /* get the size of the values array*/
    CODES_CHECK(codes_get_size(h, "values", &values_len), 0);

    values = (double*)malloc(values_len * sizeof(double));

    /* get data values*/
    CODES_CHECK(codes_get_double_array(h, "values", values, &values_len), 0);

    for (i = 0; i < values_len; i++)
        printf("%d  %.10e\n", i, values[i]);

    free(values);

    CODES_CHECK(codes_get_double(h, "max", &max), 0);
    CODES_CHECK(codes_get_double(h, "min", &min), 0);
    CODES_CHECK(codes_get_double(h, "average", &average), 0);

    printf("%d values found in %s\n", (int)values_len, filename);
    printf("max=%.10e min=%.10e average=%.10e\n", max, min, average);

    {
        /* example of accessing specific elements from data values  */
        double vals_arr[3] = { 0, 0, 0 };
        const int NUM      = 3;
        int index_arr[3];
        index_arr[0] = 0;              /* first element */
        index_arr[1] = values_len / 2; /* middle element */
        index_arr[2] = values_len - 1; /* last element */

        CODES_CHECK(codes_get_double_elements(h, "values", index_arr, NUM, vals_arr), 0);
        for (i = 0; i < NUM; ++i) {
            printf("value at index %d = %.10e\n", index_arr[i], vals_arr[i]);
        }
    }

    codes_handle_delete(h);

    fclose(in);
    return 0;
}