File: IntroExamples.html

package info (click to toggle)
hdf5 1.8.13%2Bdocs-15
links: PTS, VCS
area: main
in suites: jessie-kfreebsd
size: 171,520 kB
sloc: ansic: 387,158; f90: 35,195; sh: 20,035; xml: 17,780; cpp: 13,516; makefile: 1,487; perl: 1,299; yacc: 327; lex: 178; ruby: 37
file content (2135 lines) | stat: -rw-r--r-- 60,656 bytes
parent folder | download | duplicates (2)
<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=windows-1252">
<META NAME="Generator" CONTENT="Microsoft Word 97">
<TITLE>Introduction to HDF5</TITLE>
<link href="../ed_styles/IntroElect.css" rel="stylesheet" type="text/css">
</HEAD>
<BODY LINK="#0000ff" VLINK="#800080" bgcolor="#FFFFFF">

<!-- #BeginLibraryItem "/ed_libs/styles_Intro.lbi" -->
<!--
  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
  * 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     *
  * http://www.hdfgroup.org/HDF5/doc/Copyright.html.  If you do not have      *
  * access to either file, you may request a copy from help@hdfgroup.org.     *
  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 -->
<!-- #EndLibraryItem --><!-- #BeginLibraryItem "/ed_libs/NavBar_Intro.lbi" --><hr>
<center>
<table border=0 width=98%>
<tr><td valign=top align=left>
<a href="../H5.intro.html">Introduction to HDF5</a>&nbsp;<br>
<a href="../UG/index.html">HDF5 User Guide</a>&nbsp;
<!--
<a href="Glossary.html">Glossary</a><br>
-->
</td>
<td valign=top align=right>
<a href="../RM/RM_H5Front.html">HDF5 Reference Manual</a>&nbsp;<br>
<a href="../index.html">Other HDF5 documents and links</a>&nbsp;
</td></tr>
</table>
</center>
<hr>
<!-- #EndLibraryItem --><h1 ALIGN="CENTER">Introduction to HDF5 -- Example Codes</h1></a>


<a name="IEx-TOC">
<hr>
<center>
<table border=0 width=90%>
<tr><th colspan=3>Table of Contents</th></tr></a>
<tr><td valign=top align=left width=42%>

        <font size=-1>
            &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <A href="#CreateExample">1: Creating and writing a
              dataset</A><br>
            &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <A href="#CheckAndReadExample">2. Reading a hyperslab</A><br>
            &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <A href="#WriteSelected">3. Writing selected data</A><br>
            &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <A href="#Compound">4. Working with compound datatypes</A><br>
            &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <A href="#CreateExtendWrite">5. Creating and writing an extendible</a> <br>
              &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <A href="#CreateExtendWrite">dataset</A><br>
            &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <A href="#ReadExtended">6. Reading data</A><br>
            &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <A href="#CreateGroups">7. Creating groups</A><br>
        </font>

</td><td width=6%>&nbsp;&nbsp;</td><td valign=top align=left width=42%>

        <font size=-1>
            &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <A href="#ReadWriteAttributes">8. Writing and reading 
              attributes</A><br>
            &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <a href="#CreateWriteRefObj">9. Creating and writing references</a><br>
              &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <a href="#CreateWriteRefObj">to objects</a><br>
            &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <a href="#ReadRefObj">10. Reading references to objects</a><br>
            &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <a href="#CreateWriteRefReg">11. Creating and writing references</a><br>
              &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <a href="#CreateWriteRefReg">to dataset regions</a><br>
            &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <a href="#ReadRefReg">12. Reading references to dataset</a><br>
              &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              &nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;
              <a href="#ReadRefReg">regions</a>
        </font>
</td></tr>
</table>
</center>
<p>

<hr>



<H4><A NAME="CreateExample">Example 1: How to create a homogeneous multi-dimensional dataset</A> and write it to a file.</A></H4>
<P>This example creates a 2-dimensional HDF 5 dataset of little endian 32-bit integers.
<PRE>
<!-- Insert Example 1, h5_write.c, here. -->
/*  
 *  This example writes data to the HDF5 file.
 *  Data conversion is performed during write operation.  
 */
 
#include <hdf5.h>

#define FILE        "SDS.h5"
#define DATASETNAME "IntArray" 
#define NX     5                      /* dataset dimensions */
#define NY     6
#define RANK   2

int
main (void)
{
    hid_t       file, dataset;         /* file and dataset handles */
    hid_t       datatype, dataspace;   /* handles */
    hsize_t     dimsf[2];              /* dataset dimensions */
    herr_t      status;                             
    int         data[NX][NY];          /* data to write */
    int         i, j;

    /* 
     * Data  and output buffer initialization. 
     */
    for (j = 0; j < NX; j++) {
	for (i = 0; i < NY; i++)
	    data[j][i] = i + j;
    }     
    /*
     * 0 1 2 3 4 5 
     * 1 2 3 4 5 6
     * 2 3 4 5 6 7
     * 3 4 5 6 7 8
     * 4 5 6 7 8 9
     */

    /*
     * Create a new file using H5F_ACC_TRUNC access,
     * default file creation properties, and default file
     * access properties.
     */
    file = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

    /*
     * Describe the size of the array and create the data space for fixed
     * size dataset. 
     */
    dimsf[0] = NX;
    dimsf[1] = NY;
    dataspace = H5Screate_simple(RANK, dimsf, NULL); 

    /* 
     * Define datatype for the data in the file.
     * We will store little endian INT numbers.
     */
    datatype = H5Tcopy(H5T_NATIVE_INT);
    status = H5Tset_order(datatype, H5T_ORDER_LE);

    /*
     * Create a new dataset within the file using defined dataspace and
     * datatype and default dataset creation properties.
     */
    dataset = H5Dcreate(file, DATASETNAME, datatype, dataspace,
			H5P_DEFAULT);

    /*
     * Write the data to the dataset using default transfer properties.
     */
    status = H5Dwrite(dataset, H5T_NATIVE_INT, H5S_ALL, H5S_ALL,
		      H5P_DEFAULT, data);

    /*
     * Close/release resources.
     */
    H5Sclose(dataspace);
    H5Tclose(datatype);
    H5Dclose(dataset);
    H5Fclose(file);
 
    return 0;
}     
</pre>




<P>&nbsp;
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font>


<A NAME="CheckAndReadExample">&nbsp;</a>
<H4><A NAME="_Toc429885326">Example 2.</A> How to read a hyperslab from file into memory.</A></H4>
<P>This example reads a hyperslab from a 2-d HDF5 dataset into a 3-d dataset in memory.
<PRE>
<!-- Insert Example 2, h5_read.c, here. -->
/*  
 *   This example reads hyperslab from the SDS.h5 file 
 *   created by h5_write.c program into two-dimensional
 *   plane of the three-dimensional array. 
 *   Information about dataset in the SDS.h5 file is obtained. 
 */
 
#include "hdf5.h"

#define FILE        "SDS.h5"
#define DATASETNAME "IntArray" 
#define NX_SUB  3           /* hyperslab dimensions */ 
#define NY_SUB  4 
#define NX 7           /* output buffer dimensions */ 
#define NY 7 
#define NZ  3 
#define RANK         2
#define RANK_OUT     3

int
main (void)
{
    hid_t       file, dataset;         /* handles */
    hid_t       datatype, dataspace;   
    hid_t       memspace; 
    H5T_class_t class;                 /* datatype class */
    H5T_order_t order;                 /* data order */
    size_t      size;                  /*
				        * size of the data element	       
				        * stored in file
				        */
    hsize_t     dimsm[3];              /* memory space dimensions */
    hsize_t     dims_out[2];           /* dataset dimensions */      
    herr_t      status;                             

    int         data_out[NX][NY][NZ ]; /* output buffer */
   
    hsize_t      count[2];              /* size of the hyperslab in the file */
    hsize_t      offset[2];             /* hyperslab offset in the file */
    hsize_t      count_out[3];          /* size of the hyperslab in memory */
    hsize_t      offset_out[3];         /* hyperslab offset in memory */
    int          i, j, k, status_n, rank;

    for (j = 0; j < NX; j++) {
	for (i = 0; i < NY; i++) {
	    for (k = 0; k < NZ ; k++)
		data_out[j][i][k] = 0;
	}
    } 
 
    /*
     * Open the file and the dataset.
     */
    file = H5Fopen(FILE, H5F_ACC_RDONLY, H5P_DEFAULT);
    dataset = H5Dopen(file, DATASETNAME);

    /*
     * Get datatype and dataspace handles and then query
     * dataset class, order, size, rank and dimensions.
     */
    datatype  = H5Dget_type(dataset);     /* datatype handle */ 
    class     = H5Tget_class(datatype);
    if (class == H5T_INTEGER) printf("Data set has INTEGER type \n");
    order     = H5Tget_order(datatype);
    if (order == H5T_ORDER_LE) printf("Little endian order \n");

    size  = H5Tget_size(datatype);
    printf(" Data size is %d \n", size);

    dataspace = H5Dget_space(dataset);    /* dataspace handle */
    rank      = H5Sget_simple_extent_ndims(dataspace);
    status_n  = H5Sget_simple_extent_dims(dataspace, dims_out, NULL);
    printf("rank %d, dimensions %lu x %lu \n", rank,
	   (unsigned long)(dims_out[0]), (unsigned long)(dims_out[1]));

    /* 
     * Define hyperslab in the dataset. 
     */
    offset[0] = 1;
    offset[1] = 2;
    count[0]  = NX_SUB;
    count[1]  = NY_SUB;
    status = H5Sselect_hyperslab(dataspace, H5S_SELECT_SET, offset, NULL, 
				 count, NULL);

    /*
     * Define the memory dataspace.
     */
    dimsm[0] = NX;
    dimsm[1] = NY;
    dimsm[2] = NZ ;
    memspace = H5Screate_simple(RANK_OUT,dimsm,NULL);   

    /* 
     * Define memory hyperslab. 
     */
    offset_out[0] = 3;
    offset_out[1] = 0;
    offset_out[2] = 0;
    count_out[0]  = NX_SUB;
    count_out[1]  = NY_SUB;
    count_out[2]  = 1;
    status = H5Sselect_hyperslab(memspace, H5S_SELECT_SET, offset_out, NULL, 
				 count_out, NULL);

    /*
     * Read data from hyperslab in the file into the hyperslab in 
     * memory and display.
     */
    status = H5Dread(dataset, H5T_NATIVE_INT, memspace, dataspace,
		     H5P_DEFAULT, data_out);
    for (j = 0; j < NX; j++) {
	for (i = 0; i < NY; i++) printf("%d ", data_out[j][i][0]);
	printf("\n");
    }
    /*
     * 0 0 0 0 0 0 0
     * 0 0 0 0 0 0 0
     * 0 0 0 0 0 0 0
     * 3 4 5 6 0 0 0  
     * 4 5 6 7 0 0 0
     * 5 6 7 8 0 0 0
     * 0 0 0 0 0 0 0
     */

    /*
     * Close/release resources.
     */
    H5Tclose(datatype);
    H5Dclose(dataset);
    H5Sclose(dataspace);
    H5Sclose(memspace);
    H5Fclose(file);

    return 0;
}     
</pre>





<P>&nbsp;
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font>


<H4><A NAME="_Toc429885331"><A NAME="WriteSelected"></A>Example 3. Writing selected data from memory to a file.</A></H4>
<P>This example shows how to use the selection capabilities of HDF5 to write selected data to a file.  It includes the examples discussed in the text.

<pre>
<!-- Insert Example 3, h5_select.c, here. -->
/* 
 *  This program shows how the H5Sselect_hyperslab and H5Sselect_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.
 */ 
 
#include <hdf5.h>

#define FILE "Select.h5"

#define MSPACE1_RANK     1          /* Rank of the first dataset in memory */
#define MSPACE1_DIM      50         /* Dataset size in memory */ 

#define MSPACE2_RANK     1          /* Rank of the second dataset in memory */ 
#define MSPACE2_DIM      4          /* Dataset size in memory */ 

#define FSPACE_RANK      2          /* Dataset rank as it is stored in the file */
#define FSPACE_DIM1      8          /* Dimension sizes of the dataset as it is
                                       stored in the file */
#define FSPACE_DIM2      12 

                                    /* We will read dataset back from the file
                                       to the dataset in memory with these
                                       dataspace parameters. */  
#define MSPACE_RANK      2
#define MSPACE_DIM1      8 
#define MSPACE_DIM2      12 

#define NPOINTS          4          /* Number of points that will be selected 
                                       and overwritten */ 
int main (void)
{

   hid_t   file, dataset;           /* File and dataset identifiers */
   hid_t   mid1, mid2, fid;         /* Dataspace identifiers */
   hsize_t dim1[] = {MSPACE1_DIM};  /* Dimension size of the first dataset 
                                       (in memory) */ 
   hsize_t dim2[] = {MSPACE2_DIM};  /* Dimension size of the second dataset
                                       (in memory */ 
   hsize_t fdim[] = {FSPACE_DIM1, FSPACE_DIM2}; 
                                    /* Dimension sizes of the dataset (on disk) */

   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 */

   hsize_t coord[NPOINTS][FSPACE_RANK]; /* Array to store selected points 
                                            from the file dataspace */ 
   herr_t  ret;
   uint    i,j;
   int     matrix[MSPACE_DIM1][MSPACE_DIM2];
   int     vector[MSPACE1_DIM];
   int     values[] = {53, 59, 61, 67};  /* New values to be written */

   /*
    * Buffers' initialization.
    */
   vector[0] = vector[MSPACE1_DIM - 1] = -1;
   for (i = 1; i < MSPACE1_DIM - 1; i++) vector[i] = i;

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

    /*
     * Create a file.
     */
    file = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

    /* 
     * Create dataspace for the dataset in the file.
     */
    fid = H5Screate_simple(FSPACE_RANK, fdim, NULL);

    /*
     * Create dataset and write it into the file.
     */
    dataset = H5Dcreate(file, "Matrix in file", H5T_NATIVE_INT, fid, H5P_DEFAULT);
    ret = H5Dwrite(dataset, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, matrix);

    /*
     * Select hyperslab for the dataset in the file, using 3x2 blocks, 
     * (4,3) stride and (2,4) count starting at the position (0,1).
     */
    start[0]  = 0; start[1]  = 1;
    stride[0] = 4; stride[1] = 3;
    count[0]  = 2; count[1]  = 4;    
    block[0]  = 3; block[1]  = 2;
    ret = H5Sselect_hyperslab(fid, H5S_SELECT_SET, start, stride, count, block);

    /*
     * Create dataspace for the first dataset.
     */
    mid1 = H5Screate_simple(MSPACE1_RANK, dim1, NULL);

    /*
     * 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;
    ret = H5Sselect_hyperslab(mid1, H5S_SELECT_SET, start, stride, count, 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
     */
     ret = H5Dwrite(dataset, H5T_NATIVE_INT, mid1, fid, H5P_DEFAULT, vector);

    /*
     * Reset the selection for the file dataspace fid.
     */
    ret = H5Sselect_none(fid);

    /*
     * Create dataspace for the second dataset.
     */
    mid2 = H5Screate_simple(MSPACE2_RANK, dim2, NULL);

    /*
     * Select sequence of NPOINTS points in 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;

    ret = H5Sselect_elements(fid, H5S_SELECT_SET, NPOINTS, 
                             (const hsize_t **)coord);

    /*
     * Write new selection of points to the dataset.
     */
    ret = H5Dwrite(dataset, H5T_NATIVE_INT, mid2, fid, H5P_DEFAULT, values);   

    /*
     * 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 memory file and memory dataspaces.
     */
    ret = H5Sclose(mid1); 
    ret = H5Sclose(mid2); 
    ret = H5Sclose(fid); 
 
    /*
     * Close dataset.
     */
    ret = H5Dclose(dataset);

    /*
     * Close the file.
     */
    ret = H5Fclose(file);

    /*
     * Open the file.
     */
    file = H5Fopen(FILE, H5F_ACC_RDONLY, H5P_DEFAULT);

    /*
     * Open the dataset.
     */
    dataset = dataset = H5Dopen(file,"Matrix in file");

    /*
     * Read data back to the buffer matrix.
     */
    ret = H5Dread(dataset, H5T_NATIVE_INT, H5S_ALL, H5S_ALL,
                  H5P_DEFAULT, matrix);

    /*
     * Display the result.
     */
    for (i=0; i < MSPACE_DIM1; i++) {
        for(j=0; j < MSPACE_DIM2; j++) printf("%3d  ", matrix[i][j]);
        printf("\n");
    }

    return 0;
}
</pre>




<P>&nbsp;
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font>


<H4><A NAME="Compound"><A NAME="_Toc429885327"></A>Example 4. Working with compound datatypes.</A></H4>
<P>This example shows how to create a compound datatype, write an array which has the compound datatype to the file, and read back subsets of fields.
<PRE>
<!-- Insert Example 4, h5_compound.c, here. -->
/*
 * 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 "hdf5.h"

#define FILE          "SDScompound.h5"
#define DATASETNAME   "ArrayOfStructures"
#define LENGTH        10
#define RANK          1

int
main(void)
{

    /* First structure  and dataset*/
    typedef struct s1_t {
	int    a;
	float  b;
	double c; 
    } s1_t;
    s1_t       s1[LENGTH];
    hid_t      s1_tid;     /* File datatype identifier */

    /* Second structure (subset of s1_t)  and dataset*/
    typedef struct s2_t {
	double c;
	int    a;
    } s2_t;
    s2_t       s2[LENGTH];
    hid_t      s2_tid;    /* Memory datatype handle */

    /* Third "structure" ( will be used to read float field of s1) */
    hid_t      s3_tid;   /* Memory datatype handle */
    float      s3[LENGTH];

    int        i;
    hid_t      file, dataset, space; /* Handles */
    herr_t     status;
    hsize_t    dim[] = {LENGTH};   /* Dataspace dimensions */


    /*
     * Initialize the data
     */
    for (i = 0; i< LENGTH; i++) {
        s1[i].a = i;
        s1[i].b = i*i;
        s1[i].c = 1./(i+1);
    }

    /*
     * Create the data space.
     */
    space = H5Screate_simple(RANK, dim, NULL);

    /*
     * Create the file.
     */
    file = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

    /*
     * Create the memory datatype. 
     */
    s1_tid = H5Tcreate (H5T_COMPOUND, sizeof(s1_t));
    H5Tinsert(s1_tid, "a_name", HOFFSET(s1_t, a), H5T_NATIVE_INT);
    H5Tinsert(s1_tid, "c_name", HOFFSET(s1_t, c), H5T_NATIVE_DOUBLE);
    H5Tinsert(s1_tid, "b_name", HOFFSET(s1_t, b), H5T_NATIVE_FLOAT);

    /* 
     * Create the dataset.
     */
    dataset = H5Dcreate(file, DATASETNAME, s1_tid, space, H5P_DEFAULT);

    /*
     * Wtite data to the dataset; 
     */
    status = H5Dwrite(dataset, s1_tid, H5S_ALL, H5S_ALL, H5P_DEFAULT, s1);

    /*
     * Release resources
     */
    H5Tclose(s1_tid);
    H5Sclose(space);
    H5Dclose(dataset);
    H5Fclose(file);
 
    /*
     * Open the file and the dataset.
     */
    file = H5Fopen(FILE, H5F_ACC_RDONLY, H5P_DEFAULT);
 
    dataset = H5Dopen(file, DATASETNAME);

    /* 
     * Create a datatype for s2
     */
    s2_tid = H5Tcreate(H5T_COMPOUND, sizeof(s2_t));

    H5Tinsert(s2_tid, "c_name", HOFFSET(s2_t, c), H5T_NATIVE_DOUBLE);
    H5Tinsert(s2_tid, "a_name", HOFFSET(s2_t, a), H5T_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".
     */
    status = H5Dread(dataset, s2_tid, H5S_ALL, H5S_ALL, H5P_DEFAULT, s2);

    /*
     * Display the fields
     */
    printf("\n");
    printf("Field c : \n");
    for( i = 0; i < LENGTH; i++) printf("%.4f ", s2[i].c);
    printf("\n");

    printf("\n");
    printf("Field a : \n");
    for( i = 0; i < LENGTH; i++) printf("%d ", s2[i].a);
    printf("\n");

    /* 
     * Create a datatype for s3.
     */
    s3_tid = H5Tcreate(H5T_COMPOUND, sizeof(float));

    status = H5Tinsert(s3_tid, "b_name", 0, H5T_NATIVE_FLOAT);

    /*
     * Read field b from s1 dataset. Field in the file is found by its name.
     */
    status = H5Dread(dataset, s3_tid, H5S_ALL, H5S_ALL, H5P_DEFAULT, s3);

    /*
     * Display the field
     */
    printf("\n");
    printf("Field b : \n");
    for( i = 0; i < LENGTH; i++) printf("%.4f ", s3[i]);
    printf("\n");

    /*
     * Release resources
     */
    H5Tclose(s2_tid);
    H5Tclose(s3_tid);
    H5Dclose(dataset);
    H5Fclose(file);

    return 0;
}
</pre>




<P>&nbsp;
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font>


<H4><A NAME="CreateExtendWrite"><A NAME="_Toc429885328"></A>Example 5. Creating and writing an extendible dataset.</A></H4>
<P>This example shows how to create a 3x3 extendible dataset, to extend the dataset to 10x3, then to extend it again to 10x5.
<PRE>
<!-- Insert Example 5, h5_extend_write.c, here. -->
/*  
 *   This example shows how to work with extendible dataset.
 *   In the current version of the library dataset MUST be
 *   chunked.
 *   
 */
 
#include "hdf5.h"

#define FILE        "SDSextendible.h5"
#define DATASETNAME "ExtendibleArray" 
#define RANK         2
#define NX     10
#define NY     5 

int
main (void)
{
    hid_t       file;                          /* handles */
    hid_t       dataspace, dataset;  
    hid_t       filespace;                   
    hid_t       cparms;                     
    hsize_t      dims[2]  = { 3, 3};            /*
						 * dataset dimensions				
						 * at the creation time
						 */
    hsize_t      dims1[2] = { 3, 3};            /* data1 dimensions */ 
    hsize_t      dims2[2] = { 7, 1};            /* data2 dimensions */  
    hsize_t      dims3[2] = { 2, 2};            /* data3 dimensions */ 

    hsize_t      maxdims[2] = {H5S_UNLIMITED, H5S_UNLIMITED};
    hsize_t      chunk_dims[2] ={2, 5};
    hsize_t      size[2];
    hsize_t      offset[2];

    herr_t      status;                             

    int         data1[3][3] = { {1, 1, 1},       /* data to write */
				{1, 1, 1},
				{1, 1, 1} };      

    int         data2[7]    = { 2, 2, 2, 2, 2, 2, 2};

    int         data3[2][2] = { {3, 3},
				{3, 3} };

    /*
     * Create the data space with unlimited dimensions. 
     */
    dataspace = H5Screate_simple(RANK, dims, maxdims); 

    /*
     * Create a new file. If file exists its contents will be overwritten.
     */
    file = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

    /* 
     * Modify dataset creation properties, i.e. enable chunking.
     */
    cparms = H5Pcreate (H5P_DATASET_CREATE);
    status = H5Pset_chunk( cparms, RANK, chunk_dims);

    /*
     * Create a new dataset within the file using cparms
     * creation properties.
     */
    dataset = H5Dcreate(file, DATASETNAME, H5T_NATIVE_INT, dataspace,
			cparms);

    /*
     * Extend the dataset. This call assures that dataset is at least 3 x 3.
     */
    size[0]   = 3; 
    size[1]   = 3; 
    status = H5Dextend (dataset, size);

    /*
     * Select a hyperslab.
     */
    filespace = H5Dget_space (dataset);
    offset[0] = 0;
    offset[1] = 0;
    status = H5Sselect_hyperslab(filespace, H5S_SELECT_SET, offset, NULL,
				 dims1, NULL);  

    /*
     * Write the data to the hyperslab.
     */
    status = H5Dwrite(dataset, H5T_NATIVE_INT, dataspace, filespace,
		      H5P_DEFAULT, data1);

    /*
     * Extend the dataset. Dataset becomes 10 x 3.
     */
    dims[0]   = dims1[0] + dims2[0];
    size[0]   = dims[0];  
    size[1]   = dims[1]; 
    status = H5Dextend (dataset, size);

    /*
     * Select a hyperslab.
     */
    filespace = H5Dget_space (dataset);
    offset[0] = 3;
    offset[1] = 0;
    status = H5Sselect_hyperslab(filespace, H5S_SELECT_SET, offset, NULL,
				 dims2, NULL);  

    /*
     * Define memory space
     */
    dataspace = H5Screate_simple(RANK, dims2, NULL); 

    /*
     * Write the data to the hyperslab.
     */
    status = H5Dwrite(dataset, H5T_NATIVE_INT, dataspace, filespace,
		      H5P_DEFAULT, data2);

    /*
     * Extend the dataset. Dataset becomes 10 x 5.
     */
    dims[1]   = dims1[1] + dims3[1];
    size[0]   = dims[0];  
    size[1]   = dims[1]; 
    status = H5Dextend (dataset, size);

    /*
     * Select a hyperslab
     */
    filespace = H5Dget_space (dataset);
    offset[0] = 0;
    offset[1] = 3;
    status = H5Sselect_hyperslab(filespace, H5S_SELECT_SET, offset, NULL, 
				 dims3, NULL);  

    /*
     * Define memory space.
     */
    dataspace = H5Screate_simple(RANK, dims3, NULL); 

    /*
     * Write the data to the hyperslab.
     */
    status = H5Dwrite(dataset, H5T_NATIVE_INT, dataspace, filespace,
		      H5P_DEFAULT, data3);

    /*
     * Resulting 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
     */
    /*
     * Close/release resources.
     */
    H5Dclose(dataset);
    H5Sclose(dataspace);
    H5Sclose(filespace);
    H5Fclose(file);

    return 0;
}     
</pre>




<P>&nbsp;
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font>


<H4><A NAME="ReadExtended"><A NAME="_Toc429885329"></A>Example 6. Reading data.</A></H4>
<P>This example shows how to read information the chunked dataset written by <A HREF="#CreateExtendWrite">Example 5</A>.
<PRE>
<!-- Insert Example 6, h5_chunk_read.c, here. -->
/*  
 *   This example shows how to read data from a chunked dataset.
 *   We will read from the file created by h5_extend_write.c 
 */
 
#include "hdf5.h"

#define FILE        "SDSextendible.h5"
#define DATASETNAME "ExtendibleArray" 
#define RANK         2
#define RANKC        1
#define NX           10
#define NY           5 

int
main (void)
{
    hid_t       file;                        /* handles */
    hid_t       dataset;  
    hid_t       filespace;                   
    hid_t       memspace;                  
    hid_t       cparms;                   
    hsize_t     dims[2];                     /* dataset and chunk dimensions*/ 
    hsize_t     chunk_dims[2];
    hsize_t     col_dims[1];
    hsize_t     count[2];
    hsize_t     offset[2];

    herr_t      status, status_n;                             

    int         data_out[NX][NY];  /* buffer for dataset to be read */
    int         chunk_out[2][5];   /* buffer for chunk to be read */
    int         column[10];        /* buffer for column to be read */
    int         rank, rank_chunk;
    hsize_t	i, j;
    

 
    /*
     * Open the file and the dataset.
     */
    file = H5Fopen(FILE, H5F_ACC_RDONLY, H5P_DEFAULT);
    dataset = H5Dopen(file, DATASETNAME);
 
    /*
     * Get dataset rank and dimension.
     */

    filespace = H5Dget_space(dataset);    /* Get filespace handle first. */
    rank      = H5Sget_simple_extent_ndims(filespace);
    status_n  = H5Sget_simple_extent_dims(filespace, dims, NULL);
    printf("dataset rank %d, dimensions %lu x %lu\n",
	   rank, (unsigned long)(dims[0]), (unsigned long)(dims[1]));

    /*
     * Get creation properties list.
     */
    cparms = H5Dget_create_plist(dataset); /* Get properties handle first. */

    /* 
     * Check if dataset is chunked.
     */
    if (H5D_CHUNKED == H5Pget_layout(cparms))  {

	/*
	 * Get chunking information: rank and dimensions
	 */
	rank_chunk = H5Pget_chunk(cparms, 2, chunk_dims);
	printf("chunk rank %d, dimensions %lu x %lu\n", rank_chunk,
	       (unsigned long)(chunk_dims[0]), (unsigned long)(chunk_dims[1]));
    }
 
    /*
     * Define the memory space to read dataset.
     */
    memspace = H5Screate_simple(RANK,dims,NULL);
 
    /*
     * Read dataset back and display.
     */
    status = H5Dread(dataset, H5T_NATIVE_INT, memspace, filespace,
		     H5P_DEFAULT, data_out);
    printf("\n");
    printf("Dataset: \n");
    for (j = 0; j < dims[0]; j++) {
	for (i = 0; i < dims[1]; i++) printf("%d ", data_out[j][i]);
	printf("\n");
    }     

    /*
     *	    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.
     */
    col_dims[0] = 10;
    memspace =  H5Screate_simple(RANKC, col_dims, NULL);

    /*
     * Define the column (hyperslab) to read.
     */
    offset[0] = 0;
    offset[1] = 2;
    count[0]  = 10;
    count[1]  = 1;
    status = H5Sselect_hyperslab(filespace, H5S_SELECT_SET, offset, NULL,
				 count, NULL);
    status = H5Dread(dataset, H5T_NATIVE_INT, memspace, filespace,
		     H5P_DEFAULT, column);
    printf("\n");
    printf("Third column: \n");
    for (i = 0; i < 10; i++) {
	printf("%d \n", column[i]);
    }

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

    /*
     * Define the memory space to read a chunk.
     */
    memspace = H5Screate_simple(rank_chunk,chunk_dims,NULL);

    /*
     * Define chunk in the file (hyperslab) to read.
     */
    offset[0] = 2;
    offset[1] = 0;
    count[0]  = chunk_dims[0];
    count[1]  = chunk_dims[1];
    status = H5Sselect_hyperslab(filespace, H5S_SELECT_SET, offset, NULL, 
				 count, NULL);

    /*
     * Read chunk back and display.
     */
    status = H5Dread(dataset, H5T_NATIVE_INT, memspace, filespace,
		     H5P_DEFAULT, chunk_out);
    printf("\n");
    printf("Chunk: \n");
    for (j = 0; j < chunk_dims[0]; j++) {
	for (i = 0; i < chunk_dims[1]; i++) printf("%d ", chunk_out[j][i]);
	printf("\n");
    }     
    /*
     *	 Chunk: 
     *	 1 1 1 0 0 
     *	 2 0 0 0 0 
     */

    /*
     * Close/release resources.
     */
    H5Pclose(cparms);
    H5Dclose(dataset);
    H5Sclose(filespace);
    H5Sclose(memspace);
    H5Fclose(file);

    return 0;
}

</pre>




<P>&nbsp;
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font>


<H4><A NAME="CreateGroups"><A NAME="_Toc429885330"></A>Example 7. Creating groups.</A></H4>
<P>This example shows how to create and access a group in an 
HDF5 file and to place a dataset within this group.  
It also illustrates the usage of the <code>H5Giterate</code>, 
<code>H5Glink</code>, and <code>H5Gunlink</code> functions.

<PRE>
<!-- Insert Example 7, h5_group.c, here. -->
/*
 * This example creates a group in the file and dataset in the group. 
 * Hard link to the group object is created and the dataset is accessed
 * under different names. 
 * Iterator function is used to find the object names in the root group.
 */ 


#include "hdf5.h"


#define FILE    "group.h5"
#define RANK    2

 
herr_t file_info(hid_t loc_id, const char *name, void *opdata);
                                     /* Operator function */
int
main(void)
{

    hid_t    file;
    hid_t    grp;
    hid_t    dataset, dataspace;
    hid_t    plist; 

    herr_t   status;
    hsize_t  dims[2];
    hsize_t  cdims[2];
 
    int      idx;

    /*
     * Create a file.
     */
    file = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

    /*
     * Create a group in the file. 
     */
    grp = H5Gcreate(file, "/Data", 0);

    /*
     * Create dataset "Compressed Data" in the group using absolute
     * name. Dataset creation property list is modified to use 
     * GZIP compression with the compression effort set to 6. 
     * Note that compression can be used only when dataset is chunked. 
     */
    dims[0] = 1000;
    dims[1] = 20;
    cdims[0] = 20;
    cdims[1] = 20;
    dataspace = H5Screate_simple(RANK, dims, NULL);
    plist     = H5Pcreate(H5P_DATASET_CREATE);
                H5Pset_chunk(plist, 2, cdims);
                H5Pset_deflate( plist, 6); 
    dataset = H5Dcreate(file, "/Data/Compressed_Data", H5T_NATIVE_INT, 
                        dataspace, plist); 
 
    /* 
     * Close the dataset and the file.
     */
    H5Sclose(dataspace);
    H5Dclose(dataset);
    H5Fclose(file);

    /*
     * Now reopen the file and group in the file. 
     */
    file = H5Fopen(FILE, H5F_ACC_RDWR, H5P_DEFAULT);
    grp  = H5Gopen(file, "Data");

    /* 
     * Access "Compressed_Data" dataset in the group. 
     */
    dataset = H5Dopen(grp, "Compressed_Data");
    if( dataset < 0) printf(" Dataset is not found. \n");
    printf("\"/Data/Compressed_Data\" dataset is open \n");

    /*
     * Close the dataset.
     */
    status = H5Dclose(dataset);

    /*
     * Create hard link to the Data group.
     */
    status = H5Glink(file, H5G_LINK_HARD, "Data", "Data_new");

    /* 
     * We can access "Compressed_Data" dataset using created
     * hard link "Data_new". 
     */
    dataset = H5Dopen(file, "/Data_new/Compressed_Data");
    if( dataset < 0) printf(" Dataset is not found. \n");
    printf("\"/Data_new/Compressed_Data\" dataset is open \n");

    /*
     * Close the dataset.
     */
    status = H5Dclose(dataset);

    /* 
     * Use iterator to see the names of the objects in the file
     * root directory.
     */
    idx = H5Giterate(file, "/", NULL, file_info, NULL);

    /*
     * Unlink  name "Data" and use iterator to see the names
     * of the objects in the file root direvtory.
     */
    if (H5Gunlink(file, "Data") < 0)  
      printf(" H5Gunlink failed \n");
    else  
      printf("\"Data\" is unlinked \n");

    idx = H5Giterate(file, "/", NULL, file_info, NULL);
    

    /*
     * Close the file.
     */
     
    status = H5Fclose(file);

    return 0;
}
/*
 * Operator function.
 */
herr_t
file_info(hid_t loc_id, const char *name, void *opdata)
{
    hid_t grp;
    /*
     * Open the group using its name.
     */
    grp = H5Gopen(loc_id, name);
 
    /*
     * Display group name.
     */
    printf("\n");
    printf("Name : ");
    puts(name);
    
    H5Gclose(grp);
    return 0;
 }
</pre>




<P>&nbsp;
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font>


<H4><A NAME="_Toc429885332"><A NAME="ReadWriteAttributes">Example 8</A>. Writing and reading attributes.</A></H4>
<P>This example shows how to create HDF5 attributes, to attach them to a dataset, and to read through all of the attributes of a dataset. 

<pre>
<!-- Insert Example 8, h5_attribute.c, here. -->
/* 
 *  This program illustrates the usage of the H5A Interface functions.
 *  It creates and writes a dataset, and then creates and writes array,
 *  scalar, and string attributes of the dataset. 
 *  Program reopens the file, attaches to the scalar attribute using
 *  attribute name and reads and displays its value. Then index of the
 *  third attribute is used to read and display attribute values.
 *  The H5Aiterate function is used to iterate through the dataset attributes,
 *  and display their names. The function is also reads and displays the values 
 *  of the array attribute. 
 */ 
 
#include <stdlib.h>
#include <hdf5.h>

#define FILE "Attributes.h5"

#define RANK  1   /* Rank and size of the dataset  */ 
#define SIZE  7

#define ARANK  2   /* Rank and dimension sizes of the first dataset attribute */
#define ADIM1  2
#define ADIM2  3 
#define ANAME  "Float attribute"      /* Name of the array attribute */
#define ANAMES "Character attribute" /* Name of the string attribute */

herr_t attr_info(hid_t loc_id, const char *name, void *opdata); 
                                     /* Operator function */

int 
main (void)
{

   hid_t   file, dataset;       /* File and dataset identifiers */
   
   hid_t   fid;                 /* Dataspace identifier */
   hid_t   attr1, attr2, attr3; /* Attribute identifiers */
   hid_t   attr;
   hid_t   aid1, aid2, aid3;    /* Attribute dataspace identifiers */ 
   hid_t   atype;               /* Attribute type */

   hsize_t fdim[] = {SIZE};
   hsize_t adim[] = {ADIM1, ADIM2};  /* Dimensions of the first attribute  */
   
   float matrix[ADIM1][ADIM2]; /* Attribute data */ 

   herr_t  ret;                /* Return value */
   uint    i,j;                /* Counters */
   int     idx;                /* Attribute index */
   char    string_out[80];     /* Buffer to read string attribute back */
   int     point_out;          /* Buffer to read scalar attribute back */

   /*
    * Data initialization.
    */
   int vector[] = {1, 2, 3, 4, 5, 6, 7};  /* Dataset data */
   int point = 1;                         /* Value of the scalar attribute */ 
   char string[] = "ABCD";                /* Value of the string attribute */

   
   for (i=0; i < ADIM1; i++) {            /* Values of the array attribute */
       for (j=0; j < ADIM2; j++)
       matrix[i][j] = -1.;
   }

   /*
    * Create a file.
    */
   file = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

   /* 
    * Create the dataspace for the dataset in the file.
    */
   fid = H5Screate(H5S_SIMPLE);
   ret = H5Sset_extent_simple(fid, RANK, fdim, NULL);

   /*
    * Create the dataset in the file.
    */
   dataset = H5Dcreate(file, "Dataset", H5T_NATIVE_INT, fid, H5P_DEFAULT);

   /*
    * Write data to the dataset.
    */
   ret = H5Dwrite(dataset, H5T_NATIVE_INT, H5S_ALL , H5S_ALL, H5P_DEFAULT, vector);

   /*
    * Create dataspace for the first attribute. 
    */
   aid1 = H5Screate(H5S_SIMPLE);
   ret  = H5Sset_extent_simple(aid1, ARANK, adim, NULL);

   /*
    * Create array attribute.
    */
   attr1 = H5Acreate(dataset, ANAME, H5T_NATIVE_FLOAT, aid1, H5P_DEFAULT);

   /*
    * Write array attribute.
    */
   ret = H5Awrite(attr1, H5T_NATIVE_FLOAT, matrix);

   /*
    * Create scalar attribute.
    */
   aid2  = H5Screate(H5S_SCALAR);
   attr2 = H5Acreate(dataset, "Integer attribute", H5T_NATIVE_INT, aid2,
                     H5P_DEFAULT);

   /*
    * Write scalar attribute.
    */
   ret = H5Awrite(attr2, H5T_NATIVE_INT, &point); 

   /*
    * Create string attribute.
    */
   aid3  = H5Screate(H5S_SCALAR);
   atype = H5Tcopy(H5T_C_S1);
           H5Tset_size(atype, 4);
   attr3 = H5Acreate(dataset, ANAMES, atype, aid3, H5P_DEFAULT);

   /*
    * Write string attribute.
    */
   ret = H5Awrite(attr3, atype, string); 

   /*
    * Close attribute and file dataspaces.
    */
   ret = H5Sclose(aid1); 
   ret = H5Sclose(aid2); 
   ret = H5Sclose(aid3); 
   ret = H5Sclose(fid); 

   /*
    * Close the attributes.
    */ 
   ret = H5Aclose(attr1);
   ret = H5Aclose(attr2);
   ret = H5Aclose(attr3);
 
   /*
    * Close the dataset.
    */
   ret = H5Dclose(dataset);

   /*
    * Close the file.
    */
   ret = H5Fclose(file);

   /*
    * Reopen the file.
    */
   file = H5Fopen(FILE, H5F_ACC_RDONLY, H5P_DEFAULT);

   /*
    * Open the dataset.
    */
   dataset = H5Dopen(file,"Dataset");

   /*
    * Attach to the scalar attribute using attribute name, then read and 
    * display its value.
    */
   attr = H5Aopen_name(dataset,"Integer attribute");
   ret  = H5Aread(attr, H5T_NATIVE_INT, &point_out);
   printf("The value of the attribute \"Integer attribute\" is %d \n", point_out); 
   ret =  H5Aclose(attr);

   /*
    * Attach to the string attribute using its index, then read and display the value.
    */
   attr  = H5Aopen_idx(dataset, 2);
   atype = H5Tcopy(H5T_C_S1);
           H5Tset_size(atype, 4);
   ret   = H5Aread(attr, atype, string_out);
   printf("The value of the attribute with the index 2 is %s \n", string_out);
   ret   = H5Aclose(attr);
   ret   = H5Tclose(atype);

   /*
    * Get attribute info using iteration function. 
    */
   idx = H5Aiterate(dataset, NULL, attr_info, NULL);

   /*
    * Close the dataset and the file.
    */
   H5Dclose(dataset);
   H5Fclose(file);

   return 0;  
}

/*
 * Operator function.
 */
herr_t 
attr_info(hid_t loc_id, const char *name, void *opdata)
{
    hid_t attr, atype, aspace;  /* Attribute, datatype and dataspace identifiers */
    int   rank;
    hsize_t sdim[64]; 
    herr_t ret;
    int i;
    size_t npoints;             /* Number of elements in the array attribute. */ 
    float *float_array;         /* Pointer to the array attribute. */
    /*
     * Open the attribute using its name.
     */    
    attr = H5Aopen_name(loc_id, name);

    /*
     * Display attribute name.
     */
    printf("\n");
    printf("Name : ");
    puts(name);

    /* 
     * Get attribute datatype, dataspace, rank, and dimensions.
     */
    atype  = H5Aget_type(attr);
    aspace = H5Aget_space(attr);
    rank = H5Sget_simple_extent_ndims(aspace);
    ret = H5Sget_simple_extent_dims(aspace, sdim, NULL);

    /*
     *  Display rank and dimension sizes for the array attribute.
     */

    if(rank > 0) {
    printf("Rank : %d \n", rank); 
    printf("Dimension sizes : ");
    for (i=0; i< rank; i++) printf("%d ", (int)sdim[i]);
    printf("\n");
    }

    /*
     * Read array attribute and display its type and values.
     */

    if (H5T_FLOAT == H5Tget_class(atype)) {
    printf("Type : FLOAT \n"); 
    npoints = H5Sget_simple_extent_npoints(aspace);
    float_array = (float *)malloc(sizeof(float)*(int)npoints); 
    ret = H5Aread(attr, atype, float_array);
    printf("Values : ");
    for( i = 0; i < (int)npoints; i++) printf("%f ", float_array[i]); 
    printf("\n");
    free(float_array);
    }

    /*
     * Release all identifiers.
     */
    H5Tclose(atype);
    H5Sclose(aspace);
    H5Aclose(attr);

    return 0;
}
</pre>



<P>&nbsp;
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font>


<H4><A NAME="CreateWriteRefObj">Example 9</A>. Creating and storing references to objects.</A></H4>
This example creates a group and two datasets and a named datatype 
in the group. References to these four objects are stored in the dataset 
in the root group.  

<PRE>

#include &lt;hdf5.h&gt;

#define FILE1   "trefer1.h5"

/* 1-D dataset with fixed dimensions */
#define SPACE1_NAME  "Space1"
#define SPACE1_RANK	1
#define SPACE1_DIM1	4

/* 2-D dataset with fixed dimensions */
#define SPACE2_NAME  "Space2"
#define SPACE2_RANK	2
#define SPACE2_DIM1	10
#define SPACE2_DIM2	10

int 
main(void) {
    hid_t		fid1;		/* HDF5 File IDs		*/
    hid_t		dataset;	/* Dataset ID			*/
    hid_t		group;      /* Group ID             */
    hid_t		sid1;       /* Dataspace ID			*/
    hid_t		tid1;       /* Datatype ID			*/
    hsize_t		dims1[] = {SPACE1_DIM1};
    hobj_ref_t      *wbuf;      /* buffer to write to disk */
    int       *tu32;      /* Temporary pointer to int data */
    int        i;          /* counting variables */
    const char *write_comment="Foo!"; /* Comments for group */
    herr_t		ret;		/* Generic return value		*/

/* Compound datatype */
typedef struct s1_t {
    unsigned int a;
    unsigned int b;
    float c;
} s1_t;

    /* Allocate write buffers */
    wbuf=(hobj_ref_t *)malloc(sizeof(hobj_ref_t)*SPACE1_DIM1);
    tu32=malloc(sizeof(int)*SPACE1_DIM1);

    /* Create file */
    fid1 = H5Fcreate(FILE1, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

    /* Create dataspace for datasets */
    sid1 = H5Screate_simple(SPACE1_RANK, dims1, NULL);

    /* Create a group */
    group=H5Gcreate(fid1,"Group1",-1);

    /* Set group's comment */
    ret=H5Gset_comment(group,".",write_comment);

    /* Create a dataset (inside Group1) */
    dataset=H5Dcreate(group,"Dataset1",H5T_STD_U32LE,sid1,H5P_DEFAULT);

    for(i=0; i &lt; SPACE1_DIM1; i++)
        tu32[i] = i*3;

    /* Write selection to disk */
    ret=H5Dwrite(dataset,H5T_NATIVE_INT,H5S_ALL,H5S_ALL,H5P_DEFAULT,tu32);

    /* Close Dataset */
    ret = H5Dclose(dataset);

    /* Create another dataset (inside Group1) */
    dataset=H5Dcreate(group,"Dataset2",H5T_NATIVE_UCHAR,sid1,H5P_DEFAULT);

    /* Close Dataset */
    ret = H5Dclose(dataset);

    /* Create a datatype to refer to */
    tid1 = H5Tcreate (H5T_COMPOUND, sizeof(s1_t));

    /* Insert fields */
    ret=H5Tinsert (tid1, "a", HOFFSET(s1_t,a), H5T_NATIVE_INT);

    ret=H5Tinsert (tid1, "b", HOFFSET(s1_t,b), H5T_NATIVE_INT);

    ret=H5Tinsert (tid1, "c", HOFFSET(s1_t,c), H5T_NATIVE_FLOAT);

    /* Save datatype for later */
    ret=H5Tcommit (group, "Datatype1", tid1);

    /* Close datatype */
    ret = H5Tclose(tid1);

    /* Close group */
    ret = H5Gclose(group);

    /* Create a dataset to store references */
    dataset=H5Dcreate(fid1,"Dataset3",H5T_STD_REF_OBJ,sid1,H5P_DEFAULT);

    /* Create reference to dataset */
    ret = H5Rcreate(&wbuf[0],fid1,"/Group1/Dataset1",H5R_OBJECT,-1);

    /* Create reference to dataset */
    ret = H5Rcreate(&wbuf[1],fid1,"/Group1/Dataset2",H5R_OBJECT,-1);

    /* Create reference to group */
    ret = H5Rcreate(&wbuf[2],fid1,"/Group1",H5R_OBJECT,-1);

    /* Create reference to named datatype */
    ret = H5Rcreate(&wbuf[3],fid1,"/Group1/Datatype1",H5R_OBJECT,-1);

    /* Write selection to disk */
    ret=H5Dwrite(dataset,H5T_STD_REF_OBJ,H5S_ALL,H5S_ALL,H5P_DEFAULT,wbuf);

    /* Close disk dataspace */
    ret = H5Sclose(sid1);
    
    /* Close Dataset */
    ret = H5Dclose(dataset);

    /* Close file */
    ret = H5Fclose(fid1);
    free(wbuf);
    free(tu32);
    return 0;
}

</PRE>




<P>&nbsp;
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font>


<H4><A NAME="ReadRefObj">Example 10</A>. Reading references to objects.</A></H4>
This example opens and reads dataset <code>Dataset3</code> from 
the file created in Example 9. Then the program dereferences the references 
to dataset <code>Dataset1</code>, the group and the named datatype,
and opens those objects. 
The program reads and displays the dataset's data, the group's comment, and 
the number of members of the compound datatype.


<PRE>

#include &lt;stdlib.h&gt;
#include &lt;hdf5.h&gt;

#define FILE1   "trefer1.h5"

/* dataset with fixed dimensions */
#define SPACE1_NAME  "Space1"
#define SPACE1_RANK	1
#define SPACE1_DIM1	4

int 
main(void)
{
    hid_t		fid1;		/* HDF5 File IDs		*/
    hid_t		dataset,	/* Dataset ID			*/
                dset2;      /* Dereferenced dataset ID */
    hid_t		group;      /* Group ID             */
    hid_t		sid1;       /* Dataspace ID			*/
    hid_t		tid1;       /* Datatype ID			*/
    hobj_ref_t      *rbuf;      /* buffer to read from disk */
    int                *tu32;      /* temp. buffer read from disk */
    int        i;          /* counting variables */
    char read_comment[10];
    herr_t		ret;		/* Generic return value		*/

    /* Allocate read buffers */
    rbuf = malloc(sizeof(hobj_ref_t)*SPACE1_DIM1);
    tu32 = malloc(sizeof(int)*SPACE1_DIM1);

    /* Open the file */
    fid1 = H5Fopen(FILE1, H5F_ACC_RDWR, H5P_DEFAULT);

    /* Open the dataset */
    dataset=H5Dopen(fid1,"/Dataset3");

    /* Read selection from disk */
    ret=H5Dread(dataset,H5T_STD_REF_OBJ,H5S_ALL,H5S_ALL,H5P_DEFAULT,rbuf);

    /* Open dataset object */
    dset2 = H5Rdereference(dataset,H5R_OBJECT,&rbuf[0]);

    /* Check information in referenced dataset */
    sid1 = H5Dget_space(dset2);

    ret=H5Sget_simple_extent_npoints(sid1);

    /* Read from disk */
    ret=H5Dread(dset2,H5T_NATIVE_INT,H5S_ALL,H5S_ALL,H5P_DEFAULT,tu32);
    printf("Dataset data : \n");
     for (i=0; i &lt; SPACE1_DIM1 ; i++) printf (" %d ", tu32[i]);
    printf("\n");
    printf("\n");

    /* Close dereferenced Dataset */
    ret = H5Dclose(dset2);

    /* Open group object */
    group = H5Rdereference(dataset,H5R_OBJECT,&rbuf[2]);

    /* Get group's comment */
    ret=H5Gget_comment(group,".",10,read_comment);
    printf("Group comment is %s \n", read_comment);
    printf(" \n");
    /* Close group */
    ret = H5Gclose(group);

    /* Open datatype object */
    tid1 = H5Rdereference(dataset,H5R_OBJECT,&rbuf[3]);

    /* Verify correct datatype */
    {
        H5T_class_t tclass;

        tclass= H5Tget_class(tid1);
        if ((tclass == H5T_COMPOUND))
           printf ("Number of compound datatype members is %d \n", H5Tget_nmembers(tid1)); 
    printf(" \n");
    }

    /* Close datatype */
    ret = H5Tclose(tid1);

    /* Close Dataset */
    ret = H5Dclose(dataset);

    /* Close file */
    ret = H5Fclose(fid1);

    /* Free memory buffers */
    free(rbuf);
    free(tu32);
    return 0;
}   

</PRE>



<P>&nbsp;
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font>


<H4><A NAME="CreateWriteRefReg">Example 11</A>. Creating and writing a reference to a region.</A></H4>

This example creates a dataset in the file. Then it creates a dataset 
to store references to the dataset regions (selections).
The first selection is a 6 x 6 hyperslab. 
The second selection is a point selection in the same dataset.
References to both selections are created and stored in the buffer, 
and then written to the dataset in the file.

<pre>
#include &lt;stdlib.h&gt;
#include &lt;hdf5.h&gt;

#define FILE2	"trefer2.h5"
#define SPACE1_NAME  "Space1"
#define SPACE1_RANK     1
#define SPACE1_DIM1     4

/* Dataset with fixed dimensions */
#define SPACE2_NAME  "Space2"
#define SPACE2_RANK	2
#define SPACE2_DIM1	10
#define SPACE2_DIM2	10

/* Element selection information */
#define POINT1_NPOINTS 10

int
main(void)
{
    hid_t	fid1;		/* HDF5 File IDs		*/
    hid_t	dset1,		/* Dataset ID			*/
                dset2;      /* Dereferenced dataset ID */
    hid_t	sid1,       /* Dataspace ID	#1		*/
                sid2;       /* Dataspace ID	#2		*/
    hsize_t	dims1[] = {SPACE1_DIM1},
            	dims2[] = {SPACE2_DIM1, SPACE2_DIM2};
    hsize_t	start[SPACE2_RANK];     /* Starting location of hyperslab */
    hsize_t	stride[SPACE2_RANK];    /* Stride of hyperslab */
    hsize_t	count[SPACE2_RANK];     /* Element count of hyperslab */
    hsize_t	block[SPACE2_RANK];     /* Block size of hyperslab */
    hsize_t	coord1[POINT1_NPOINTS][SPACE2_RANK]; 
                                    /* Coordinates for point selection */
    hdset_reg_ref_t      *wbuf;      /* buffer to write to disk */
    int     *dwbuf;      /* Buffer for writing numeric data to disk */
    int        i;          /* counting variables */
    herr_t		ret;		/* Generic return value		*/


    /* Allocate write & read buffers */
    wbuf=calloc(sizeof(hdset_reg_ref_t), SPACE1_DIM1);
    dwbuf=malloc(sizeof(int)*SPACE2_DIM1*SPACE2_DIM2);

    /* Create file */
    fid1 = H5Fcreate(FILE2, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

    /* Create dataspace for datasets */
    sid2 = H5Screate_simple(SPACE2_RANK, dims2, NULL);

    /* Create a dataset */
    dset2=H5Dcreate(fid1,"Dataset2",H5T_STD_U8LE,sid2,H5P_DEFAULT);

    for(i=0; i &lt; SPACE2_DIM1*SPACE2_DIM2; i++)
        dwbuf[i]=i*3;

    /* Write selection to disk */
    ret=H5Dwrite(dset2,H5T_NATIVE_INT,H5S_ALL,H5S_ALL,H5P_DEFAULT,dwbuf);

    /* Close Dataset */
    ret = H5Dclose(dset2);

    /* Create dataspace for the reference dataset */
    sid1 = H5Screate_simple(SPACE1_RANK, dims1, NULL);

    /* Create a dataset */
    dset1=H5Dcreate(fid1,"Dataset1",H5T_STD_REF_DSETREG,sid1,H5P_DEFAULT);

    /* Create references */

    /* Select 6x6 hyperslab for first reference */
    start[0]=2; start[1]=2;
    stride[0]=1; stride[1]=1;
    count[0]=6; count[1]=6;
    block[0]=1; block[1]=1;
    ret = H5Sselect_hyperslab(sid2,H5S_SELECT_SET,start,stride,count,block);

    /* Store first dataset region */
    ret = H5Rcreate(&wbuf[0],fid1,"/Dataset2",H5R_DATASET_REGION,sid2);

    /* Select sequence of ten points for second reference */
    coord1[0][0]=6; coord1[0][1]=9;
    coord1[1][0]=2; coord1[1][1]=2;
    coord1[2][0]=8; coord1[2][1]=4;
    coord1[3][0]=1; coord1[3][1]=6;
    coord1[4][0]=2; coord1[4][1]=8;
    coord1[5][0]=3; coord1[5][1]=2;
    coord1[6][0]=0; coord1[6][1]=4;
    coord1[7][0]=9; coord1[7][1]=0;
    coord1[8][0]=7; coord1[8][1]=1;
    coord1[9][0]=3; coord1[9][1]=3;
    ret = H5Sselect_elements(sid2,H5S_SELECT_SET,POINT1_NPOINTS,(const hsize_t **)coord1);

    /* Store second dataset region */
    ret = H5Rcreate(&wbuf[1],fid1,"/Dataset2",H5R_DATASET_REGION,sid2);

    /* Write selection to disk */
    ret=H5Dwrite(dset1,H5T_STD_REF_DSETREG,H5S_ALL,H5S_ALL,H5P_DEFAULT,wbuf);

    /* Close all objects */
    ret = H5Sclose(sid1);
    ret = H5Dclose(dset1);
    ret = H5Sclose(sid2);
    
    /* Close file */
    ret = H5Fclose(fid1);

    free(wbuf);
    free(dwbuf);
    return 0;
}   

</pre>



<P>&nbsp;
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font>


<H4><A NAME="ReadRefReg">Example 12</A>. Reading a reference to a region.</A></H4>

This example reads a dataset containing dataset region references.
It reads data from the dereferenced dataset and displays the number of 
elements and raw data. Then it reads two selections:
a hyperslab selection and a point selection. The program queries a 
number of points in the hyperslab  and the coordinates and displays them. 
Then it queries a number of selected points and their coordinates and 
displays the information.

<PRE>
   
#include &lt;stdlib.h&gt;
#include &lt;hdf5.h&gt;

#define FILE2	"trefer2.h5"
#define NPOINTS 10
 
/* 1-D dataset with fixed dimensions */
#define SPACE1_NAME  "Space1"
#define SPACE1_RANK	1
#define SPACE1_DIM1	4

/* 2-D dataset with fixed dimensions */
#define SPACE2_NAME  "Space2"
#define SPACE2_RANK	2
#define SPACE2_DIM1	10
#define SPACE2_DIM2	10

int 
main(void)
{
    hid_t		fid1;		/* HDF5 File IDs		*/
    hid_t		dset1,	/* Dataset ID			*/
                dset2;      /* Dereferenced dataset ID */
    hid_t		sid1,       /* Dataspace ID	#1		*/
                sid2;       /* Dataspace ID	#2		*/
    hsize_t *   coords;             /* Coordinate buffer */
    hsize_t		low[SPACE2_RANK];   /* Selection bounds */
    hsize_t		high[SPACE2_RANK];     /* Selection bounds */
    hdset_reg_ref_t      *rbuf;      /* buffer to to read disk */
    int    *drbuf;      /* Buffer for reading numeric data from disk */
    int        i, j;          /* counting variables */
    herr_t		ret;		/* Generic return value		*/

    /* Output message about test being performed */

    /* Allocate write & read buffers */
    rbuf=malloc(sizeof(hdset_reg_ref_t)*SPACE1_DIM1);
    drbuf=calloc(sizeof(int),SPACE2_DIM1*SPACE2_DIM2);

    /* Open the file */
    fid1 = H5Fopen(FILE2, H5F_ACC_RDWR, H5P_DEFAULT);

    /* Open the dataset */
    dset1=H5Dopen(fid1,"/Dataset1");

    /* Read selection from disk */
    ret=H5Dread(dset1,H5T_STD_REF_DSETREG,H5S_ALL,H5S_ALL,H5P_DEFAULT,rbuf);

    /* Try to open objects */
    dset2 = H5Rdereference(dset1,H5R_DATASET_REGION,&rbuf[0]);

    /* Check information in referenced dataset */
    sid1 = H5Dget_space(dset2);

    ret=H5Sget_simple_extent_npoints(sid1);
    printf(" Number of elements in the dataset is : %d\n",ret);

    /* Read from disk */
    ret=H5Dread(dset2,H5T_NATIVE_INT,H5S_ALL,H5S_ALL,H5P_DEFAULT,drbuf);

    for(i=0; i &lt; SPACE2_DIM1; i++) {
        for (j=0; j &lt; SPACE2_DIM2; j++) printf (" %d ", drbuf[i*SPACE2_DIM2+j]);
        printf("\n"); }

    /* Get the hyperslab selection */
    sid2=H5Rget_region(dset1,H5R_DATASET_REGION,&rbuf[0]);

    /* Verify correct hyperslab selected */
    ret = H5Sget_select_npoints(sid2);
    printf(" Number of elements in the hyperslab is : %d \n", ret);
    ret = H5Sget_select_hyper_nblocks(sid2);
    coords=malloc(ret*SPACE2_RANK*sizeof(hsize_t)*2); /* allocate space for the hyperslab blocks */
    ret = H5Sget_select_hyper_blocklist(sid2,0,ret,coords);
    printf(" Hyperslab coordinates are : \n");
    printf (" ( %lu , %lu ) ( %lu , %lu ) \n", \
(unsigned long)coords[0],(unsigned long)coords[1],(unsigned long)coords[2],(unsigned long)coords[3]); 
    free(coords);
    ret = H5Sget_select_bounds(sid2,low,high);

    /* Close region space */
    ret = H5Sclose(sid2);

    /* Get the element selection */
    sid2=H5Rget_region(dset1,H5R_DATASET_REGION,&rbuf[1]);

    /* Verify correct elements selected */
    ret = H5Sget_select_elem_npoints(sid2);
    printf(" Number of selected elements is : %d\n", ret);

    /* Allocate space for the element points */
    coords= malloc(ret*SPACE2_RANK*sizeof(hsize_t)); 
    ret = H5Sget_select_elem_pointlist(sid2,0,ret,coords);
    printf(" Coordinates of selected elements are : \n");
    for (i=0; i &lt; 2*NPOINTS; i=i+2) 
         printf(" ( %lu , %lu ) \n", (unsigned long)coords[i],(unsigned long)coords[i+1]); 
          
    free(coords);
    ret = H5Sget_select_bounds(sid2,low,high);

    /* Close region space */
    ret = H5Sclose(sid2);

    /* Close first space */
    ret = H5Sclose(sid1);

    /* Close dereferenced Dataset */
    ret = H5Dclose(dset2);

    /* Close Dataset */
    ret = H5Dclose(dset1);

    /* Close file */
    ret = H5Fclose(fid1);

    /* Free memory buffers */
    free(rbuf);
    free(drbuf);
    return 0;
}   

</PRE>


<P>&nbsp;
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font> 


<!-- #BeginLibraryItem "/ed_libs/NavBar_Intro.lbi" --><hr>
<center>
<table border=0 width=98%>
<tr><td valign=top align=left>
<a href="../H5.intro.html">Introduction to HDF5</a>&nbsp;<br>
<a href="../UG/index.html">HDF5 User Guide</a>&nbsp;
<!--
<a href="Glossary.html">Glossary</a><br>
-->
</td>
<td valign=top align=right>
<a href="../RM/RM_H5Front.html">HDF5 Reference Manual</a>&nbsp;<br>
<a href="../index.html">Other HDF5 documents and links</a>&nbsp;
</td></tr>
</table>
</center>
<hr>
<!-- #EndLibraryItem --><address>

<!-- #BeginLibraryItem "/ed_libs/Footer.lbi" -->
<address>
<table width="100%" border="0">
  <tr valign="top">
      <td align="left">
          <address>
          The HDF Group Help Desk: <img src="../Graphics/help.png" align=top height=16>
          <br>
          Describes HDF5 Release 1.8.13, May 2014.
          </address>
      </td><td width="5%">&nbsp;</td>
      <td align="right">
          <a href="../Copyright.html">Copyright</a> by
          <a href="http://www.hdfgroup.org">The HDF Group</a>
          <br>
          and the Board of Trustees of the University of Illinois
      </td>   
  </tr>   
</table>
</address>
<!-- #EndLibraryItem -->
 
Last modified: 3 August 2004
 

</BODY>
</HTML>