HDF5 C++ API Reference Manual

 

 

 

writedata.cpp

This example shows how to write datasets.

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * 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 program shows how the select_hyperslab and select_elements
 *  functions are used to write selected data from memory to the file.
 *  Program takes 48 elements from the linear buffer and writes them into
 *  the matrix using 3x2 blocks, (4,3) stride and (2,4) count.
 *  Then four elements  of the matrix are overwritten with the new values and
 *  file is closed. Program reopens the file and reads and displays the result.
 */

#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( "Select.h5" );
const H5std_string DATASET_NAME( "Matrix in file" );
const int   MSPACE1_RANK = 1;   // Rank of the first dataset in memory
const int   MSPACE1_DIM = 50;   // Dataset size in memory
const int   MSPACE2_RANK = 1;   // Rank of the second dataset in memory
const int   MSPACE2_DIM = 4;    // Dataset size in memory
const int   FSPACE_RANK = 2;    // Dataset rank as it is stored in the file
const int   FSPACE_DIM1 = 8;    // Dimension sizes of the dataset as it is...
const int   FSPACE_DIM2 = 12;   // ...stored in the file
const int   MSPACE_DIM1 = 8;    // We will read dataset back from the file...
const int   MSPACE_DIM2 = 12;   // ...to the dataset in memory with these ...
                                // ...dataspace parameters
const int   NPOINTS = 4;        // Number of points that will be selected...
                                //    ...and overwritten

int main (void)
{
#ifdef SKIP_UNTIL_APRIL_2009
   /*
   * Buffers' initialization.
   */
   int   i,j;
   int    vector[MSPACE1_DIM];
   vector[0] = vector[MSPACE1_DIM - 1] = -1;
   for (i = 1; i < MSPACE1_DIM - 1; i++)
      vector[i] = i;

   int    matrix[MSPACE_DIM1][MSPACE_DIM2];
   for (i = 0; i < MSPACE_DIM1; i++)
   {
      for (j = 0; j < MSPACE_DIM2; j++)
         matrix[i][j] = 0;
   }

   // 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 a file.
       */
      H5File* file = new H5File( FILE_NAME, H5F_ACC_TRUNC );

      /*
       * Create dataspace for the dataset in the file.
       */
      hsize_t fdim[] = {FSPACE_DIM1, FSPACE_DIM2}; // dim sizes of ds (on disk)
      DataSpace fspace( FSPACE_RANK, fdim );

      /*
       * Create dataset and write it into the file.
       */
      DataSet* dataset = new DataSet(
            file->createDataSet( DATASET_NAME, PredType::NATIVE_INT, fspace ));
      dataset->write( matrix, PredType::NATIVE_INT );

      /*
       * Select hyperslab for the dataset in the file, using 3x2 blocks,
       * (4,3) stride and (2,4) count starting at the position (0,1).
       */
      hsize_t start[2]; // Start of hyperslab
      hsize_t stride[2]; // Stride of hyperslab
      hsize_t count[2];  // Block count
      hsize_t block[2];  // Block sizes
      start[0]  = 0; start[1]  = 1;
      stride[0] = 4; stride[1] = 3;
      count[0]  = 2; count[1]  = 4;
      block[0]  = 3; block[1]  = 2;
      fspace.selectHyperslab( H5S_SELECT_SET, count, start, stride, block);

      /*
       * Create dataspace for the first dataset.
       */
      hsize_t dim1[] = {MSPACE1_DIM};  /* Dimension size of the first dataset
                                         (in memory) */
      DataSpace mspace1( MSPACE1_RANK, dim1 );

      /*
       * Select hyperslab.
       * We will use 48 elements of the vector buffer starting at the
       * second element.  Selected elements are 1 2 3 . . . 48
       */
      start[0]  = 1;
      stride[0] = 1;
      count[0]  = 48;
      block[0]  = 1;
      mspace1.selectHyperslab( H5S_SELECT_SET, count, start, stride, block);

      /*
       * Write selection from the vector buffer to the dataset in the file.
       *
       * File dataset should look like this:
       *                    0  1  2  0  3  4  0  5  6  0  7  8
       *                    0  9 10  0 11 12  0 13 14  0 15 16
       *                    0 17 18  0 19 20  0 21 22  0 23 24
       *                    0  0  0  0  0  0  0  0  0  0  0  0
       *                    0 25 26  0 27 28  0 29 30  0 31 32
       *                    0 33 34  0 35 36  0 37 38  0 39 40
       *                    0 41 42  0 43 44  0 45 46  0 47 48
       *                    0  0  0  0  0  0  0  0  0  0  0  0
       */
       dataset->write( vector, PredType::NATIVE_INT, mspace1, fspace );

      /*
       * Reset the selection for the file dataspace fid.
       */
      fspace.selectNone();

      /*
       * Create dataspace for the second dataset.
       */
      hsize_t dim2[] = {MSPACE2_DIM};  /* Dimension size of the second dataset
                                         (in memory */
      DataSpace mspace2( MSPACE2_RANK, dim2 );

      /*
       * Select sequence of NPOINTS points in the file dataspace.
       */
      hsize_t coord[NPOINTS][FSPACE_RANK]; /* Array to store selected points
                                              from the file dataspace */
      coord[0][0] = 0; coord[0][1] = 0;
      coord[1][0] = 3; coord[1][1] = 3;
      coord[2][0] = 3; coord[2][1] = 5;
      coord[3][0] = 5; coord[3][1] = 6;

      fspace.selectElements( H5S_SELECT_SET, NPOINTS, (const hsize_t *)coord);

      /*
       * Write new selection of points to the dataset.
       */
      int    values[] = {53, 59, 61, 67};  /* New values to be written */
      dataset->write( values, PredType::NATIVE_INT, mspace2, fspace );

      /*
       * File dataset should look like this:
       *                   53  1  2  0  3  4  0  5  6  0  7  8
       *                    0  9 10  0 11 12  0 13 14  0 15 16
       *                    0 17 18  0 19 20  0 21 22  0 23 24
       *                    0  0  0 59  0 61  0  0  0  0  0  0
       *                    0 25 26  0 27 28  0 29 30  0 31 32
       *                    0 33 34  0 35 36 67 37 38  0 39 40
       *                    0 41 42  0 43 44  0 45 46  0 47 48
       *                    0  0  0  0  0  0  0  0  0  0  0  0
       *
       */

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

      /*
       * Open the file.
       */
      file = new H5File( FILE_NAME, H5F_ACC_RDONLY );

      /*
       * Open the dataset.
       */
      dataset = new DataSet( file->openDataSet( DATASET_NAME ));

      /*
       * Read data back to the buffer matrix.
       */
      dataset->read( matrix, PredType::NATIVE_INT );

      /*
       * Display the result.
       */
      for (i=0; i < MSPACE_DIM1; i++)
      {
          for(j=0; j < MSPACE_DIM2; j++)
             cout << matrix[i][j] << "  ";
          cout << endl;
      }

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

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