HDF5 C++ API Reference Manual

 

 

 

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 files COPYING and Copyright.html.  COPYING can be found at the root   *
 * of the source code distribution tree; Copyright.html can be found at the  *
 * root level of an installed copy of the electronic HDF5 document set and   *
 * is linked from the top-level documents page.  It can also be found at     *
 * https://support.hdfgroup.org/HDF5/doc/Copyright.html.  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
#include <string>

#ifndef H5_NO_NAMESPACE
#ifndef H5_NO_STD
    using std::cout;
    using std::endl;
#endif  // H5_NO_STD
#endif

#include "H5Cpp.h"

#ifndef H5_NO_NAMESPACE
using namespace H5;
#endif

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, void *opdata);

int main(void)
{
#ifdef SKIP_UNTIL_APRIL_2009
    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( RANK, dims ); // create the new dataspace
                                         // for the dataset

      DSetCreatPropList ds_creatplist;  // create dataset creation prop list
      ds_creatplist.setChunk( 2, cdims );  // then modify it for compression
      ds_creatplist.setDeflate( 6 );

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

      /*
       * Close the dataset and the file.
       */
      delete dataset;
      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( H5G_LINK_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 = H5Giterate(file->getId(), "/", 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 = H5Giterate(file->getId(), "/", NULL, file_info, NULL);
      cout << endl;

      /*
       * Close the file.
       */
      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;
   }
#endif
   return 0;
}

/*
 * Operator function.
 */
herr_t
file_info(hid_t loc_id, const char *name, void *opdata)
{
    hid_t group;
    /*
     * Open the group using its name.
     */
    group = H5Gopen(loc_id, name);

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

    H5Gclose(group);
    return 0;
 }

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