h5group.cpp

This example shows how to work with groups.

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright by The HDF Group.                                               *
 * Copyright by the Board of Trustees of the University of Illinois.         *
 * All rights reserved.                                                      *
 *                                                                           *
 * This file is part of HDF5.  The full HDF5 copyright notice, including     *
 * terms governing use, modification, and redistribution, is contained in    *
 * the COPYING file, which can be found at the root of the source code       *
 * distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.  *
 * If you do not have access to either file, you may request a copy from     *
 * help@hdfgroup.org.                                                        *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/*
 * This example creates a group in the file and dataset in the group.
 * Hard link to the group object is created and the dataset is accessed
 * under different names.
 * Iterator function is used to find the object names in the root group.
 * Note that the C++ API iterator function is not completed yet, thus
 * the C version is used in this example.
 */

#ifdef OLD_HEADER_FILENAME
#include <iostream.h>
#else
#include <iostream>
#endif
using std::cout;
using std::endl;

#include <string>
#include "H5Cpp.h"
using namespace H5;

const H5std_string FILE_NAME( "Group.h5" );
const int      RANK = 2;

// Operator function
extern "C" herr_t file_info(hid_t loc_id, const char *name, const H5L_info_t *linfo,
    void *opdata);

int main(void)
{

    hsize_t  dims[2];
    hsize_t  cdims[2];

    // Try block to detect exceptions raised by any of the calls inside it
    try
    {
    /*
     * Turn off the auto-printing when failure occurs so that we can
     * handle the errors appropriately
     */
    Exception::dontPrint();

    /*
     * Create the named file, truncating the existing one if any,
     * using default create and access property lists.
     */
    H5File *file = new H5File( FILE_NAME, H5F_ACC_TRUNC );

    /*
     * Create a group in the file
     */
    Group* group = new Group( file->createGroup( "/Data" ));

    /*
     * Create dataset "Compressed Data" in the group using absolute
     * name. Dataset creation property list is modified to use
     * GZIP compression with the compression effort set to 6.
     * Note that compression can be used only when dataset is chunked.
     */
    dims[0] = 1000;
    dims[1] = 20;
    cdims[0] = 20;
    cdims[1] = 20;
    DataSpace *dataspace = new DataSpace(RANK, dims); // create new dspace
    DSetCreatPropList ds_creatplist;  // create dataset creation prop list
    ds_creatplist.setChunk( 2, cdims );  // then modify it for compression
    ds_creatplist.setDeflate( 6 );

    /*
     * Create the first dataset.
     */
    DataSet* dataset = new DataSet(file->createDataSet(
        "/Data/Compressed_Data", PredType::NATIVE_INT,
        *dataspace, ds_creatplist ));

    /*
     * Close the first dataset.
     */
    delete dataset;
    delete dataspace;

    /*
     * Create the second dataset.
     */
    dims[0] = 500;
    dims[1] = 20;
    dataspace = new DataSpace(RANK, dims); // create second dspace
    dataset = new DataSet(file->createDataSet("/Data/Float_Data",
            PredType::NATIVE_FLOAT, *dataspace));

    delete dataset;
    delete dataspace;
    delete group;
    delete file;

    /*
     * Now reopen the file and group in the file.
     */
    file = new H5File(FILE_NAME, H5F_ACC_RDWR);
    group = new Group(file->openGroup("Data"));

    /*
     * Access "Compressed_Data" dataset in the group.
     */
    try {  // to determine if the dataset exists in the group
        dataset = new DataSet( group->openDataSet( "Compressed_Data" ));
    }
    catch( GroupIException not_found_error ) {
        cout << " Dataset is not found." << endl;
    }
    cout << "dataset \"/Data/Compressed_Data\" is open" << endl;

    /*
     * Close the dataset.
     */
    delete dataset;

    /*
     * Create hard link to the Data group.
     */
    file->link( H5L_TYPE_HARD, "Data", "Data_new" );

    /*
     * We can access "Compressed_Data" dataset using created
     * hard link "Data_new".
     */
    try {  // to determine if the dataset exists in the file
        dataset = new DataSet(file->openDataSet( "/Data_new/Compressed_Data" ));
    }
    catch( FileIException not_found_error )
    {
        cout << " Dataset is not found." << endl;
    }
    cout << "dataset \"/Data_new/Compressed_Data\" is open" << endl;

    /*
     * Close the dataset.
     */
    delete dataset;

    /*
     * Use iterator to see the names of the objects in the file
     * root directory.
     */
    cout << endl << "Iterating over elements in the file" << endl;
    herr_t idx = H5Literate(file->getId(), H5_INDEX_NAME, H5_ITER_INC, NULL, file_info, NULL);
    cout << endl;

    /*
     * Unlink  name "Data" and use iterator to see the names
     * of the objects in the file root direvtory.
     */
    cout << "Unlinking..." << endl;
    try {  // attempt to unlink the dataset
        file->unlink( "Data" );
    }
    catch( FileIException unlink_error )
    {
        cout << " unlink failed." << endl;
    }
    cout << "\"Data\" is unlinked" << endl;

    cout << endl << "Iterating over elements in the file again" << endl;
    idx = H5Literate(file->getId(), H5_INDEX_NAME, H5_ITER_INC, NULL, file_info, NULL);
    cout << endl;

    /*
     * Close the group and file.
     */
    delete group;
    delete file;
    }  // end of try block

    // catch failure caused by the H5File operations
    catch( FileIException error )
    {
    error.printError();
    return -1;
    }

    // catch failure caused by the DataSet operations
    catch( DataSetIException error )
    {
    error.printError();
    return -1;
    }

    // catch failure caused by the DataSpace operations
    catch( DataSpaceIException error )
    {
    error.printError();
    return -1;
    }

    // catch failure caused by the Attribute operations
    catch( AttributeIException error )
    {
    error.printError();
    return -1;
    }
    return 0;
}

/*
 * Operator function.
 */
herr_t
file_info(hid_t loc_id, const char *name, const H5L_info_t *linfo, void *opdata)
{
    hid_t group;

    /*
     * Open the group using its name.
     */
    group = H5Gopen2(loc_id, name, H5P_DEFAULT);

    /*
     * Display group name.
     */
    cout << "Name : " << name << endl;

    H5Gclose(group);
    return 0;
}