compound.cpp

This example shows how to create a compound datatype, write an array which has the compound datatype to the file, and read back fields' subsets.

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright by The HDF Group.                                               *
 * 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://www.hdfgroup.org/licenses.               *
 * If you do not have access to either file, you may request a copy from     *
 * help@hdfgroup.org.                                                        *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
 
/*
 * This example shows how to create a compound datatype,
 * write an array which has the compound datatype to the file,
 * and read back fields' subsets.
 */
 
#include <iostream>
using std::cout;
using std::endl;
 
#include <string>
#include "H5Cpp.h"
using namespace H5;
 
const H5std_string FILE_NAME("SDScompound.h5");
const H5std_string DATASET_NAME("ArrayOfStructures");
const H5std_string MEMBER1("a_name");
const H5std_string MEMBER2("b_name");
const H5std_string MEMBER3("c_name");
const int          LENGTH = 10;
const int          RANK   = 1;
 
int
main(void)
{
    /* First structure  and dataset*/
    typedef struct s1_t {
        int    a;
        float  b;
        double c;
    } s1_t;
 
    /* Second structure (subset of s1_t)  and dataset*/
    typedef struct s2_t {
        double c;
        int    a;
    } s2_t;
 
    // Try block to detect exceptions raised by any of the calls inside it
    try {
        /*
         * Initialize the data
         */
        int  i;
        s1_t s1[LENGTH];
        for (i = 0; i < LENGTH; i++) {
            s1[i].a = i;
            s1[i].b = i * i;
            s1[i].c = 1. / (i + 1);
        }
 
        /*
         * Turn off the auto-printing when failure occurs so that we can
         * handle the errors appropriately
         */
        Exception::dontPrint();
 
        /*
         * Create the data space.
         */
        hsize_t   dim[] = {LENGTH}; /* Dataspace dimensions */
        DataSpace space(RANK, dim);
 
        /*
         * Create the file.
         */
        H5File *file = new H5File(FILE_NAME, H5F_ACC_TRUNC);
 
        /*
         * Create the memory datatype.
         */
        CompType mtype1(sizeof(s1_t));
        mtype1.insertMember(MEMBER1, HOFFSET(s1_t, a), PredType::NATIVE_INT);
        mtype1.insertMember(MEMBER3, HOFFSET(s1_t, c), PredType::NATIVE_DOUBLE);
        mtype1.insertMember(MEMBER2, HOFFSET(s1_t, b), PredType::NATIVE_FLOAT);
 
        /*
         * Create the dataset.
         */
        DataSet *dataset;
        dataset = new DataSet(file->createDataSet(DATASET_NAME, mtype1, space));
 
        /*
         * Write data to the dataset;
         */
        dataset->write(s1, mtype1);
 
        /*
         * Release resources
         */
        delete dataset;
        delete file;
 
        /*
         * Open the file and the dataset.
         */
        file    = new H5File(FILE_NAME, H5F_ACC_RDONLY);
        dataset = new DataSet(file->openDataSet(DATASET_NAME));
 
        /*
         * Create a datatype for s2
         */
        CompType mtype2(sizeof(s2_t));
 
        mtype2.insertMember(MEMBER3, HOFFSET(s2_t, c), PredType::NATIVE_DOUBLE);
        mtype2.insertMember(MEMBER1, HOFFSET(s2_t, a), PredType::NATIVE_INT);
 
        /*
         * Read two fields c and a from s1 dataset. Fields in the file
         * are found by their names "c_name" and "a_name".
         */
        s2_t s2[LENGTH];
        dataset->read(s2, mtype2);
 
        /*
         * Display the fields
         */
        cout << endl << "Field c : " << endl;
        for (i = 0; i < LENGTH; i++)
            cout << s2[i].c << " ";
        cout << endl;
 
        cout << endl << "Field a : " << endl;
        for (i = 0; i < LENGTH; i++)
            cout << s2[i].a << " ";
        cout << endl;
 
        /*
         * Create a datatype for s3.
         */
        CompType mtype3(sizeof(float));
 
        mtype3.insertMember(MEMBER2, 0, PredType::NATIVE_FLOAT);
 
        /*
         * Read field b from s1 dataset. Field in the file is found by its name.
         */
        float s3[LENGTH]; // Third "structure" - used to read float field of s1
        dataset->read(s3, mtype3);
 
        /*
         * Display the field
         */
        cout << endl << "Field b : " << endl;
        for (i = 0; i < LENGTH; i++)
            cout << s3[i] << " ";
        cout << endl;
 
        /*
         * Release resources
         */
        delete dataset;
        delete file;
    } // 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;
    }
 
    // catch failure caused by the DataSpace operations
    catch (DataTypeIException error) {
        error.printErrorStack();
        return -1;
    }
 
    return 0;
}