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://www.hdfgroup.org/licenses.               *
 * 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.
 */
 
#include <iostream>
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.printErrorStack();
        return -1;
    }
 
    // catch failure caused by the DataSet operations
    catch (DataSetIException error) {
        error.printErrorStack();
        return -1;
    }
 
    // catch failure caused by the DataSpace operations
    catch (DataSpaceIException error) {
        error.printErrorStack();
        return -1;
    }
 
    // catch failure caused by the Attribute operations
    catch (AttributeIException error) {
        error.printErrorStack();
        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;
}