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<HTML><HEAD>
<TITLE>HDF5 Tutorial - Selections using H5Sselect_hyperslab
</TITLE>
</HEAD>
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<H1>
<BIG><BIG><BIG><FONT COLOR="#c101cd">Selections using H5Sselect_hyperslab</FONT>
</BIG></BIG></BIG></H1>
<hr noshade size=1>
<BODY>
<H2>Contents:</H2>
<UL>
<LI><A HREF="#def">Selecting a Portion of a Dataspace</A>
<LI>Programming Example
<UL>
<LI> <A HREF="#desc">Description</A>
<LI> <A HREF="#rem">Remarks</A>
<!--
<LI> <A HREF="#fc">File Contents</A>
-->
</UL>
</UL>
<HR>
<A NAME="def">
<H2>Selecting a Portion of a Dataspace</H2>
Hyperslabs are portions of datasets. A hyperslab selection can be a logically contiguous collection of points in a dataspace, or it
can be a regular pattern of points or blocks in a dataspace.
You can select a hyperslab to write to/read from with the function
H5Sselect_hyperslab.
<P>
<H2> Programming Example</H2>
<A NAME="desc">
<H3><U>Description</U></H3>
This example creates a 5 x 6 integer array in a
file called sds.h5. It selects a 3 x 4 hyperslab from the dataset,
as follows (Dimension 0 is offset by 1 and Dimension 1 is offset by 2):
<P>
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<P>
Then it reads the hyperslab from this file into a 2-dimensional plane
(size 7 x 7) of a 3-dimensional array (size 7 x 7 x 3), as
follows (with Dimension 0 offset by 3):
<P>
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<P>
[ <A HREF="examples/h5_hyperslab.c">Download h5_hyperslab.c</A> ]
<PRE>
/************************************************************
This example shows how to write and read a hyperslab. It
is derived from the h5_read.c and h5_write.c examples in
the "Introduction to HDF5".
************************************************************/
#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
#define X 5 /* dataset dimensions */
#define Y 6
int
main (void)
{
hsize_t dimsf[2]; /* dataset dimensions */
int data[X][Y]; /* data to write */
/*
* Data and output buffer initialization.
*/
hid_t file, dataset; /* handles */
hid_t dataspace;
hid_t memspace;
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;
/*********************************************************
This writes data to the HDF5 file.
*********************************************************/
/*
* Data and output buffer initialization.
*/
for (j = 0; j < X; j++) {
for (i = 0; i < Y; 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,
* the default file creation properties, and the 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] = X;
dimsf[1] = Y;
dataspace = H5Screate_simple (RANK, dimsf, NULL);
/*
* Create a new dataset within the file using defined dataspace and
* default dataset creation properties.
*/
dataset = H5Dcreate (file, DATASETNAME, H5T_STD_I32BE, 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);
H5Dclose (dataset);
H5Fclose (file);
/*************************************************************
This reads the hyperslab from the sds.h5 file just
created, into a 2-dimensional plane of the 3-dimensional
array.
************************************************************/
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);
dataspace = H5Dget_space (dataset); /* dataspace handle */
rank = H5Sget_simple_extent_ndims (dataspace);
status_n = H5Sget_simple_extent_dims (dataspace, dims_out, NULL);
printf("\nRank: %d\nDimensions: %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);
printf ("Data:\n ");
for (j = 0; j < NX; j++) {
for (i = 0; i < NY; i++) printf("%d ", data_out[j][i][0]);
printf("\n ");
}
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 and release resources.
*/
H5Dclose (dataset);
H5Sclose (dataspace);
H5Sclose (memspace);
H5Fclose (file);
}
</PRE>
<A NAME="rem">
<H3><U>Remarks</U></H3>
<UL>
<LI>H5Sselect_hyperslab selects a hyperslab region to add to the current
selected region for a specified dataspace.
<PRE>
herr_t H5Sselect_hyperslab (hid_t space_id, H5S_seloper_t op,
const hssize_t *start, const hsize_t *stride,
const hsize_t *count, const hsize_t *block )
</PRE>
<UL>
<LI>The first parameter, <I>space_id</I>, is the dataspace identifier for the
specified dataspace.
<LI>The second parameter, <I>op</I>, can only be set to H5S_SELECT_SET
in the current release. It replaces the existing selection with the
parameters from this call. Overlapping blocks are not supported.
<LI>The <I>start</I> array determines the starting coordinates of the hyperslab to select.
<LI>The <I>stride</I> array indicates which elements along a dimension are to
be selected.
<LI>The <I>count</I> array determines how many positions to select from the
dataspace in each dimension.
<LI>The <I>block</I> array determines the size of the element block selected
by the dataspace.
</UL>
<P>
The <I>start</I>, <I>stride</I>, <I>count</I>, and <I>block</I> arrays must
be the same size as the rank of the dataspace.
<P>
<LI>This example introduces the following H5Dget_* functions:
<UL>
<B>H5Dget_space:</B> returns an identifier for a copy of the dataspace
of a dataset.<BR>
<B>H5Dget_type:</B> returns an identifier for a copy of the data type
of a dataset.<BR>
</UL>
<P>
<LI>This example introduces the following H5Sget_* functions used to
obtain information about selections:
<UL>
<B>H5Sget_simple_extent_dims:</B> returns the size and maximum sizes
of each dimension of a dataspace.<BR>
<B>H5Sget_simple_extent_ndims:</B> determines the dimensionality
(or rank) of a dataspace. <BR>
</UL>
</UL>
</UL>
</PRE>
<P>
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<BR> <H6>Last Modified: August 27, 1999</H6><BR>
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