h5ex_t_opaqueatt.c

/************************************************************

  This example shows how to read and write opaque datatypes
  to an attribute.  The program first writes opaque data to
  an attribute with a dataspace of DIM0, then closes the
  file. Next, it reopens the file, reads back the data, and
  outputs it to the screen.

 ************************************************************/

#include "hdf5.h"
#include <stdio.h>
#include <stdlib.h>

#define FILENAME  "h5ex_t_opaqueatt.h5"
#define DATASET   "DS1"
#define ATTRIBUTE "A1"
#define DIM0      4
#define LEN       7

int
main(void)
{
    hid_t   file, space, dtype, dset, attr; /* Handles */
    herr_t  status;
    hsize_t dims[1] = {DIM0};
    size_t  len;
    char    wdata[DIM0 * LEN], /* Write buffer */
        *rdata,                /* Read buffer */
        str[LEN] = "OPAQUE", *tag;
    int     ndims;
    hsize_t i, j;

    /*
     * Initialize data.
     */
    for (i = 0; i < DIM0; i++) {
        for (j = 0; j < LEN - 1; j++)
            wdata[j + i * LEN] = str[j];
        wdata[LEN - 1 + i * LEN] = (char)i + '0';
    }

    /*
     * Create a new file using the default properties.
     */
    file = H5Fcreate(FILENAME, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

    /*
     * Create dataset with a null dataspace.
     */
    space  = H5Screate(H5S_NULL);
    dset   = H5Dcreate(file, DATASET, H5T_STD_I32LE, space, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
    status = H5Sclose(space);

    /*
     * Create opaque datatype and set the tag to something appropriate.
     * For this example we will write and view the data as a character
     * array.
     */
    dtype  = H5Tcreate(H5T_OPAQUE, LEN);
    status = H5Tset_tag(dtype, "Character array");

    /*
     * Create dataspace.  Setting maximum size to NULL sets the maximum
     * size to be the current size.
     */
    space = H5Screate_simple(1, dims, NULL);

    /*
     * Create the attribute and write the opaque data to it.
     */
    attr   = H5Acreate(dset, ATTRIBUTE, dtype, space, H5P_DEFAULT, H5P_DEFAULT);
    status = H5Awrite(attr, dtype, wdata);

    /*
     * Close and release resources.
     */
    status = H5Aclose(attr);
    status = H5Dclose(dset);
    status = H5Sclose(space);
    status = H5Tclose(dtype);
    status = H5Fclose(file);

    /*
     * Now we begin the read section of this example.  Here we assume
     * the attribute has the same name and rank, but can have any size.
     * Therefore we must allocate a new array to read in data using
     * malloc().
     */

    /*
     * Open file, dataset, and attribute.
     */
    file = H5Fopen(FILENAME, H5F_ACC_RDONLY, H5P_DEFAULT);
    dset = H5Dopen(file, DATASET, H5P_DEFAULT);
    attr = H5Aopen(dset, ATTRIBUTE, H5P_DEFAULT);

    /*
     * Get datatype and properties for the datatype.  Note that H5Tget_tag
     * allocates space for the string in tag, so we must remember to release it
     * later.
     */
    dtype = H5Aget_type(attr);
    len   = H5Tget_size(dtype);
    tag   = H5Tget_tag(dtype);

    /*
     * Get dataspace and allocate memory for read buffer.
     */
    space = H5Aget_space(attr);
    ndims = H5Sget_simple_extent_dims(space, dims, NULL);
    rdata = (char *)malloc(dims[0] * len);

    /*
     * Read the data.
     */
    status = H5Aread(attr, dtype, rdata);

    /*
     * Output the data to the screen.
     */
    printf("Datatype tag for %s is: \"%s\"\n", ATTRIBUTE, tag);
    for (i = 0; i < dims[0]; i++) {
        printf("%s[%" PRIuHSIZE "]: ", ATTRIBUTE, i);
        for (j = 0; j < len; j++)
            printf("%c", rdata[j + i * len]);
        printf("\n");
    }

    /*
     * Close and release resources.
     */
    free(rdata);
#if H5_VERSION_GE(1, 10, 0) && !defined(H5_USE_18_API) && !defined(H5_USE_16_API)
    H5free_memory(tag);
#else
    free(tag);
#endif
    status = H5Aclose(attr);
    status = H5Dclose(dset);
    status = H5Sclose(space);
    status = H5Tclose(dtype);
    status = H5Fclose(file);

    return 0;
}