eccodes/examples/C/grib_get_keys.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_get_keys
 *
 * Description: how to get values using keys from GRIB messages
 *
 */
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include "eccodes.h"

int main(int argc, char** argv)
{
    int err           = 0;
    float* fvalues    = NULL; /* data values as floats */
    double* dvalues   = NULL; /* data values as doubles */
    size_t values_len = 0;
    size_t i = 0, len = 0;

    double latitudeOfFirstGridPointInDegrees;
    double longitudeOfFirstGridPointInDegrees;
    double latitudeOfLastGridPointInDegrees;
    double longitudeOfLastGridPointInDegrees;

    double jDirectionIncrementInDegrees;
    double iDirectionIncrementInDegrees;

    long numberOfPointsAlongAParallel;
    long numberOfPointsAlongAMeridian;

    double daverage    = 0;
    float  faverage    = 0;
    char* packingType = NULL;

    FILE* in             = NULL;
    const char* filename = "../../data/regular_latlon_surface.grib1";
    codes_handle* h      = NULL;

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

    /* create new handle from the first message in the 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;
    }
    fclose(in);

    /* store the filename in the key "file" for this handle */
    len = strlen(filename);
    CODES_CHECK(codes_set_string(h, "file", filename, &len), 0);

    /* get as a long*/
    CODES_CHECK(codes_get_long(h, "Ni", &numberOfPointsAlongAParallel), 0);
    printf("numberOfPointsAlongAParallel=%ld\n", numberOfPointsAlongAParallel);

    /* get as a long*/
    CODES_CHECK(codes_get_long(h, "Nj", &numberOfPointsAlongAMeridian), 0);
    printf("numberOfPointsAlongAMeridian=%ld\n", numberOfPointsAlongAMeridian);

    /* get as a double*/
    CODES_CHECK(codes_get_double(h, "latitudeOfFirstGridPointInDegrees", &latitudeOfFirstGridPointInDegrees), 0);
    printf("latitudeOfFirstGridPointInDegrees=%g\n", latitudeOfFirstGridPointInDegrees);

    /* get as a double*/
    CODES_CHECK(codes_get_double(h, "longitudeOfFirstGridPointInDegrees", &longitudeOfFirstGridPointInDegrees), 0);
    printf("longitudeOfFirstGridPointInDegrees=%g\n", longitudeOfFirstGridPointInDegrees);

    /* get as a double*/
    CODES_CHECK(codes_get_double(h, "latitudeOfLastGridPointInDegrees", &latitudeOfLastGridPointInDegrees), 0);
    printf("latitudeOfLastGridPointInDegrees=%g\n", latitudeOfLastGridPointInDegrees);

    /* get as a double*/
    CODES_CHECK(codes_get_double(h, "longitudeOfLastGridPointInDegrees", &longitudeOfLastGridPointInDegrees), 0);
    printf("longitudeOfLastGridPointInDegrees=%g\n", longitudeOfLastGridPointInDegrees);

    /* get as a double*/
    CODES_CHECK(codes_get_double(h, "jDirectionIncrementInDegrees", &jDirectionIncrementInDegrees), 0);
    printf("jDirectionIncrementInDegrees=%g\n", jDirectionIncrementInDegrees);

    /* get as a double*/
    CODES_CHECK(codes_get_double(h, "iDirectionIncrementInDegrees", &iDirectionIncrementInDegrees), 0);
    printf("iDirectionIncrementInDegrees=%g\n", iDirectionIncrementInDegrees);

    /* get as string */
    CODES_CHECK(codes_get_length(h, "packingType", &len), 0);
    packingType = (char*)malloc(len * sizeof(char));
    codes_get_string(h, "packingType", packingType, &len);
    printf("packingType=%s\n", packingType);
    free(packingType);

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

    fvalues = (float*)malloc(values_len * sizeof(float));
    dvalues = (double*)malloc(values_len * sizeof(double));

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

    faverage = 0;
    daverage = 0;
    for (i = 0; i < values_len; i++) {
        faverage += fvalues[i];
        daverage += dvalues[i];
    }

    faverage /= (float)values_len;
    daverage /= (double)values_len;

    free(fvalues);
    free(dvalues);
    printf("There are %zu values, double average is %g\n", values_len, daverage);
    printf("There are %zu values, float average is  %f\n", values_len, faverage);

    {
        int eq = 0;
        /* now retrieve the value of the key "file" */
        char file[256] = {0,};
        CODES_CHECK(codes_get_length(h, "file", &len), 0);
        assert(len == 1 + strlen(filename));
        codes_get_string(h, "file", file, &len);
        eq = strcmp(file, filename);
        if (eq != 0) assert(!"file and filename not equal");
    }

    {
        /* example of getting bytes */
        const char* name        = "reservedNeedNotBePresent";
        unsigned char* byte_val = NULL;
        size_t keySize          = 0;
        CODES_CHECK(codes_get_size(h, name, &keySize), 0);
        byte_val = (unsigned char*)malloc(keySize * sizeof(unsigned char));
        GRIB_CHECK(codes_get_bytes(h, name, byte_val, &keySize), name);
        free(byte_val);
    }

    codes_handle_delete(h);

    return 0;
}