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<TITLE>Introduction to HDF5</TITLE>
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<a href="../H5.intro.html">Introduction to HDF5</a> <br>
<a href="../H5.user.html">HDF5 User Guide</a>
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<td valign=top align=right>
<a href="../RM_H5Front.html">HDF5 Reference Manual</a> <br>
<a href="../index.html">Other HDF5 documents and links</a>
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<!-- #EndLibraryItem --><h1 ALIGN="CENTER">Introduction to HDF5 -- Example Codes</h1></a>
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<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>
   
<A href="#CreateExample">1: Creating and writing a
dataset</A><br>
   
<A href="#CheckAndReadExample">2. Reading a hyperslab</A><br>
   
<A href="#WriteSelected">3. Writing selected data</A><br>
   
<A href="#Compound">4. Working with compound datatypes</A><br>
   
<A href="#CreateExtendWrite">5. Creating and writing an extendible</a> <br>
   
   
<A href="#CreateExtendWrite">dataset</A><br>
   
<A href="#ReadExtended">6. Reading data</A><br>
   
<A href="#CreateGroups">7. Creating groups</A><br>
</font>
</td><td width=6%> </td><td valign=top align=left width=42%>
<font size=-1>
   
<A href="#ReadWriteAttributes">8. Writing and reading
attributes</A><br>
   
<a href="#CreateWriteRefObj">9. Creating and writing references</a><br>
   
   
<a href="#CreateWriteRefObj">to objects</a><br>
   
<a href="#ReadRefObj">10. Reading references to objects</a><br>
   
<a href="#CreateWriteRefReg">11. Creating and writing references</a><br>
   
   
<a href="#CreateWriteRefReg">to dataset regions</a><br>
   
<a href="#ReadRefReg">12. Reading references to dataset</a><br>
   
   
<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>
<p align=right><font size=-1><a href="#IEx-TOC">(Return to TOC)</a></font>
<A NAME="CheckAndReadExample"> </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 */
hssize_t offset[2]; /* hyperslab offset in the file */
hsize_t count_out[3]; /* size of the hyperslab in memory */
hssize_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>
<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) */
hssize_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 */
hssize_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 hssize_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>
<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>
<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];
hssize_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
*
* 3 3 3 2 2
* 3 3 3 2 2
* 3 3 3 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>
<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];
hssize_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>
<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>
<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>
<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 <hdf5.h>
#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 < 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>
<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 <stdlib.h>
#include <hdf5.h>
#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 < 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>
<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 <stdlib.h>
#include <hdf5.h>
#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};
hssize_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 */
hssize_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 < 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 hssize_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>
<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 <stdlib.h>
#include <hdf5.h>
#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 < SPACE2_DIM1; i++) {
for (j=0; j < 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 < 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>
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