hdf5/c++/examples/chunks.cpp

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * 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 shows how to read data from a chunked dataset.
 *   We will read from the file created by extend.cpp
 */

#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( "SDSextendible.h5" );
const H5std_string DATASET_NAME( "ExtendibleArray" );
const int      NX = 10;
const int      NY = 5;
const int      RANK = 2;
const int      RANKC = 1;

int main (void)
{
    hsize_t	i, j;

    // 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();

	/*
	 * Open the file and the dataset.
	 */
	H5File file( FILE_NAME, H5F_ACC_RDONLY );
	DataSet dataset = file.openDataSet( DATASET_NAME );

	/*
	 * Get filespace for rank and dimension
	 */
	DataSpace filespace = dataset.getSpace();

	/*
	 * Get number of dimensions in the file dataspace
	 */
	int rank = filespace.getSimpleExtentNdims();

	/*
	 * Get and print the dimension sizes of the file dataspace
	 */
	hsize_t dims[2]; 	// dataset dimensions
	rank = filespace.getSimpleExtentDims( dims );
	cout << "dataset rank = " << rank << ", dimensions "
	     << (unsigned long)(dims[0]) << " x "
	     << (unsigned long)(dims[1]) << endl;

	/*
	 * Define the memory space to read dataset.
	 */
	DataSpace mspace1(RANK, dims);

	/*
	 * Read dataset back and display.
	 */
	int data_out[NX][NY];  // buffer for dataset to be read
	dataset.read( data_out, PredType::NATIVE_INT, mspace1, filespace );

	cout << "\n";
	cout << "Dataset: \n";
	for (j = 0; j < dims[0]; j++)
	{
	    for (i = 0; i < dims[1]; i++)
		cout << data_out[j][i] << " ";
	    cout << endl;
	}

	/*
	 *	    dataset rank 2, dimensions 10 x 5
	 *	    chunk rank 2, dimensions 2 x 5

	 *	    Dataset:
	 *	    1 1 1 3 3
	 *	    1 1 1 3 3
	 *	    1 1 1 0 0
	 *	    2 0 0 0 0
	 *	    2 0 0 0 0
	 *	    2 0 0 0 0
	 *	    2 0 0 0 0
	 *	    2 0 0 0 0
	 *	    2 0 0 0 0
	 *	    2 0 0 0 0
	 */

	/*
	 * Read the third column from the dataset.
	 * First define memory dataspace, then define hyperslab
	 * and read it into column array.
	 */
	hsize_t col_dims[1];
	col_dims[0] = 10;
	DataSpace mspace2( RANKC, col_dims );

	/*
	 * Define the column (hyperslab) to read.
	 */
	hsize_t offset[2] = { 0, 2 };
	hsize_t  count[2] = { 10, 1 };
	int column[10];  // buffer for column to be read

	/*
	 * Define hyperslab and read.
	 */
	filespace.selectHyperslab( H5S_SELECT_SET, count, offset );
	dataset.read( column, PredType::NATIVE_INT, mspace2, filespace );

	cout << endl;
	cout << "Third column: " << endl;
	for (i = 0; i < 10; i++)
	    cout << column[i] << endl;

	/*
	 *	    Third column:
	 *	    1
	 *	    1
	 *	    1
	 *	    0
	 *	    0
	 *	    0
	 *	    0
	 *	    0
	 *	    0
	 *	    0
	 */

	/*
	 * Get creation properties list.
	 */
	DSetCreatPropList cparms = dataset.getCreatePlist();

	/*
	 * Check if dataset is chunked.
	 */
	hsize_t chunk_dims[2];
	int     rank_chunk;
	if( H5D_CHUNKED == cparms.getLayout() )
	{
	    /*
	     * Get chunking information: rank and dimensions
	     */
	    rank_chunk = cparms.getChunk( 2, chunk_dims);
	    cout << "chunk rank " << rank_chunk << "dimensions "
		<< (unsigned long)(chunk_dims[0]) << " x "
		<< (unsigned long)(chunk_dims[1]) << endl;

	    /*
	     * Define the memory space to read a chunk.
	     */
	    DataSpace mspace3( rank_chunk, chunk_dims );

	    /*
	     * Define chunk in the file (hyperslab) to read.
	     */
	    offset[0] = 2;
	    offset[1] = 0;
	    count[0]  = chunk_dims[0];
	    count[1]  = chunk_dims[1];
	    filespace.selectHyperslab( H5S_SELECT_SET, count, offset );

	    /*
	     * Read chunk back and display.
	     */
	    int chunk_out[2][5];   // buffer for chunk to be read
	    dataset.read( chunk_out, PredType::NATIVE_INT, mspace3, filespace );
	    cout << endl;
	    cout << "Chunk:" << endl;
	    for (j = 0; j < chunk_dims[0]; j++)
	    {
		for (i = 0; i < chunk_dims[1]; i++)
		    cout << chunk_out[j][i] << " ";
		cout << endl;
	    }
	    /*
	     *	 Chunk:
	     *	 1 1 1 0 0
	     *	 2 0 0 0 0
	     */
	}
    }  // 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;
    }
    return 0;
}