h5ex_t_vlenatt.c

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

  This example shows how to read and write variable-length
  datatypes to an attribute.  The program first writes two
  variable-length integer arrays to the attribute 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_vlenatt.h5"
#define DATASET   "DS1"
#define ATTRIBUTE "A1"
#define LEN0      3
#define LEN1      12

int
main(void)
{
    hid_t file, filetype, memtype, space, dset, attr;
    /* Handles */
    herr_t status;
    hvl_t  wdata[2], /* Array of vlen structures */
        *rdata;      /* Pointer to vlen structures */
    hsize_t dims[1] = {2};
    int    *ptr, ndims;
    hsize_t i, j;

    /*
     * Initialize variable-length data.  wdata[0] is a countdown of
     * length LEN0, wdata[1] is a Fibonacci sequence of length LEN1.
     */
    wdata[0].len = LEN0;
    ptr          = (int *)malloc(wdata[0].len * sizeof(int));
    for (i = 0; i < wdata[0].len; i++)
        ptr[i] = wdata[0].len - (size_t)i; /* 3 2 1 */
    wdata[0].p = (void *)ptr;

    wdata[1].len = LEN1;
    ptr          = (int *)malloc(wdata[1].len * sizeof(int));
    ptr[0]       = 1;
    ptr[1]       = 1;
    for (i = 2; i < wdata[1].len; i++)
        ptr[i] = ptr[i - 1] + ptr[i - 2]; /* 1 1 2 3 5 8 etc. */
    wdata[1].p = (void *)ptr;

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

    /*
     * Create variable-length datatype for file and memory.
     */
    filetype = H5Tvlen_create(H5T_STD_I32LE);
    memtype  = H5Tvlen_create(H5T_NATIVE_INT);

    /*
     * 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 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 variable-length data to it
     */
    attr   = H5Acreate(dset, ATTRIBUTE, filetype, space, H5P_DEFAULT, H5P_DEFAULT);
    status = H5Awrite(attr, memtype, wdata);

    /*
     * Close and release resources.  Note the use of H5Dvlen_reclaim
     * removes the need to manually free() the previously malloc'ed
     * data.
     */
    status = H5Dvlen_reclaim(memtype, space, H5P_DEFAULT, wdata);
    status = H5Aclose(attr);
    status = H5Dclose(dset);
    status = H5Sclose(space);
    status = H5Tclose(filetype);
    status = H5Tclose(memtype);
    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 dataspace and allocate memory for array of vlen structures.
     * This does not actually allocate memory for the vlen data, that
     * will be done by the library.
     */
    space = H5Aget_space(attr);
    ndims = H5Sget_simple_extent_dims(space, dims, NULL);
    rdata = (hvl_t *)malloc(dims[0] * sizeof(hvl_t));

    /*
     * Create the memory datatype.
     */
    memtype = H5Tvlen_create(H5T_NATIVE_INT);

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

    /*
     * Output the variable-length data to the screen.
     */
    for (i = 0; i < dims[0]; i++) {
        printf("%s[%" PRIuHSIZE "]:\n  {", ATTRIBUTE, i);
        ptr = rdata[i].p;
        for (j = 0; j < rdata[i].len; j++) {
            printf(" %d", ptr[j]);
            if ((j + 1) < rdata[i].len)
                printf(",");
        }
        printf(" }\n");
    }

    /*
     * Close and release resources.  Note we must still free the
     * top-level pointer "rdata", as H5Dvlen_reclaim only frees the
     * actual variable-length data, and not the structures themselves.
     */
    status = H5Dvlen_reclaim(memtype, space, H5P_DEFAULT, rdata);
    free(rdata);
    status = H5Aclose(attr);
    status = H5Dclose(dset);
    status = H5Sclose(space);
    status = H5Tclose(memtype);
    status = H5Fclose(file);

    return 0;
}