/*
 * Use of HDF5 named data types to implement quantities with a unit.
 * Copyright © 2013 Peter Colberg.
 * Licensed under the MIT License (Expat).
 */

#include <hdf5.h>

int main(void)
{
    /* open HDF5 file for writing */
    hid_t file = H5Fcreate("h5md_units.h5", H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

    /* create units group */
    hid_t group = H5Gcreate(file, "units", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);

    /* create acceleration data type and store in units group */
    hid_t filetype = H5Tcopy(H5T_NATIVE_DOUBLE);
    H5Tcommit(group, "acceleration", filetype, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
    H5Gclose(group);

    /* attach unit attribute to acceleration data type */
    char *buf[1] = {"meter per square second"};
    hid_t space = H5Screate(H5S_SCALAR);
    hid_t strtype = H5Tcopy(H5T_C_S1);
    H5Tset_size(strtype, H5T_VARIABLE);
    H5Tset_cset(strtype, H5T_CSET_UTF8);
    hid_t attr = H5Acreate(filetype, "unit", strtype, space, H5P_DEFAULT, H5P_DEFAULT);
    H5Awrite(attr, strtype, buf);
    H5Aclose(attr);
    H5Tclose(strtype);

    /* create attribute using acceleration data type */
    double data = 9.81;
    attr = H5Acreate(file, "data", filetype, space, H5P_DEFAULT, H5P_DEFAULT);
    H5Awrite(attr, H5T_NATIVE_DOUBLE, &data);
    H5Aclose(attr);
    H5Sclose(space);
    H5Tclose(filetype);
    H5Fclose(file);

    return 0;
}