hdf5/c++/examples/chunks.cpp

/*  
 *   This example shows how to read data from a chunked dataset.
 *   We will read from the file created by extend.C 
 */
 
#include <string>
#ifndef H5_NO_NAMESPACE
using namespace std;
#endif

#ifdef OLD_HEADER_FILENAME
#include <iostream.h>
#else
#include <iostream>
#endif
#include "H5Cpp.h"

#ifndef H5_NO_NAMESPACE
using namespace H5;
#endif

const string FILE_NAME( "SDSextendible.h5" );
const 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
   {
      /*
       * Open the file and the dataset.
       */
      H5File file( FILE_NAME, H5F_ACC_RDONLY );
      DataSet dataset = file.openDataSet( DATASET_NAME );
 
      /*
       * Get dataset rank and dimension.
       */
      // Get filespace first.
      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;

      /*
       * 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 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.
       */
      hssize_t offset[2] = { 0, 2 };
      hsize_t  count[2] = { 10, 1 };
      int      column[10];        // buffer for column to be 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 
       */

      /*
       * 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();
   }

   // catch failure caused by the DataSet operations
   catch( DataSetIException error )
   {
      error.printError();
   }

   // catch failure caused by the DataSpace operations
   catch( DataSpaceIException error )
   {
      error.printError();
   }

   return 0;
}