hdf5/examples/Attributes.txt

Attribute Examples: 

H5Acreate2 example: Show how to create an attribute for a dataset and a group
----------------
{
    hid_t file;
    hid_t group;
    hid_t dataset;
    hid_t attr;
    hid_t dataspace;
    int32 attr_data;
    int rank;
    size_t dimsf[2];

    /* Open the file */
    file=H5Fopen("example.h5", H5F_ACC_RDWR, H5P_DEFAULT);

    /* Describe the size of the array and create the data space */
    rank=2;
    dimsf[0] = H5S_UNLIMITED;
    dimsf[1] = H5S_UNLIMITED;
    dataspace = H5Screate_simple(rank, dimsf, NULL); 

    /* Create a dataset */
    dataset = H5Dcreate2(file, "Dataset1", H5T_UINT8, dataspace, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);

    <Write data to first dataset>

    /* Create an attribute for the dataset */
    attr = H5Acreate2(dataset, "Attr1", H5T_INT32, H5S_SCALAR, H5P_DEFAULT, H5P_DEFAULT);

    /* Write attribute information */
    H5Awrite(attr, H5T_INT32, &attr_data);

    /* Close attribute */
    H5Aclose(attr);

    /* Close dataset */
    H5Dclose(dataset);

    /* Create a group */
    group = H5Gcreate2(file, "/Group One", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);

    /* Create an attribute for the dataset */
    attr = H5Acreate2(group, "Attr1", H5T_INT32, H5S_SCALAR, H5P_DEFAULT, H5P_DEFAULT);

    /* Write attribute information */
    H5Awrite(attr, H5T_INT32, &attr_data);

    /* Close attribute */
    H5Aclose(attr);

    /* Close the group */
    H5Gclose(group);

    /* Close file */
    H5Fclose(file);
}


H5Aiterate example: Print all the names of attributes of a dataset, without
                        any buffers.
---------------------

herr_t print_names (hid_t loc_id, const char *name, void *opdata)
{
    puts (name);
    return 0;
}

{
    H5Aiterate (dataset_or_group_id, NULL, print_names, NULL);
}


H5Aread Example: Attach to an attribute of a dataset and read in attr. data
----------------
{
    hid_t file;
    hid_t dataset;
    hid_t attr;
    int32 attr_data;

    /* Open the file */
    file=H5Fopen("example.h5", H5F_ACC_RDWR, H5P_DEFAULT);

    /* Open the dataset */
    dataset=H5Dopen2(file, "Dataset1", H5P_DEFAULT);

    /* Get the OID of the attribute */
    attr=H5Aopen(dataset, "Attr1", H5P_DEFAULT);

    /* Read attribute */
    H5Aread(attr,H5T_INT32,attr_data);

    /* Close attribute dataset */
    H5Aclose(attr);

    /* Close first dataset */
    H5Dclose(dataset);

    /* Close file */
    H5Fclose(file);
}

H5Alink Example: Shows how to share an attribute between two datasets.
----------------
{
    hid_t file;
    hid_t dataset1, dataset2;
    hid_t attr;

    /* Open the file */
    file=H5Fopen("example.h5", H5F_ACC_RDWR, H5P_DEFAULT);

    /* Open the first dataset */
    dataset1=H5Dopen2(file, "Dataset1", H5P_DEFAULT);

    /* Open the first dataset */
    dataset2=H5Dopen2(file, "Dataset2", H5P_DEFAULT);

    /* Get the OID of the attribute */
    attr=H5Aopen(dataset1, "Foo", H5P_DEFAULT);

    /* 
     * Create an attribute in the second dataset to the attribute in dataset1,
     * changing the name of the attribute information in dataset2.
     */
    H5Alink(dataset2, attr, "Bar");

    /* Close attribute dataset */
    H5Aclose(attr);

    /* Close datasets */
    H5Dclose(dataset1);
    H5Dclose(dataset2);

    /* Close file */
    H5Fclose(file);
}