HDF5 C++ API  1.10.0
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chunks.cpp
This example shows how to read data from a chunked dataset.
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* 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 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
#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( "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
*/
/*
* 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.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;
}
return 0;
}


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