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authorFrank Baker <fbaker@hdfgroup.org>2000-12-22 20:47:59 (GMT)
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+<HTML><HEAD>
+<TITLE>HDF5 Tutorial - Selections using H5Sselect_hyperslab
+</TITLE>
+</HEAD>
+
+<body bgcolor="#ffffff">
+
+<!-- BEGIN MAIN BODY -->
+
+<A HREF="http://www.ncsa.uiuc.edu/"><img border=0
+src="http://www.ncsa.uiuc.edu/Images/NCSAhome/footerlogo.gif"
+width=78 height=27 alt="NCSA"><P></A>
+
+ [ <A HREF="title.html"><I>HDF5 Tutorial Top</I></A> ]
+<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>
+<TABLE BORDER CELLSPACING=1 CELLPADDING=7 WIDTH=172>
+<TR><TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+</TR>
+<TR><TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="17%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="17%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="17%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+</TR>
+<TR><TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="17%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="17%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="17%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+</TR>
+<TR><TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="17%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="17%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="17%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+</TR>
+<TR><TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="17%" VALIGN="TOP">&nbsp;</TD>
+</TR>
+</TABLE>
+<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>
+<TABLE BORDER CELLSPACING=1 CELLPADDING=7 WIDTH=201>
+<TR><TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+</TR>
+<TR><TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+</TR>
+<TR><TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+</TR>
+<TR><TD WIDTH="14%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="14%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="14%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="14%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+</TR>
+<TR><TD WIDTH="14%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="14%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="14%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="14%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+</TR>
+<TR><TD WIDTH="14%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="14%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="14%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="14%" VALIGN="TOP">
+<FONT SIZE=2><P> X</FONT></TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+</TR>
+<TR><TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+<TD WIDTH="14%" VALIGN="TOP">&nbsp;</TD>
+</TR>
+</TABLE>
+<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>
+
+<!--
+<A NAME="fc">
+<H3><U>File Contents</U></H3>
+-->
+
+
+
+
+
+<!-- BEGIN FOOTER INFO -->
+
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+ width=78 height=27 alt="NCSA"><br>
+ The National Center for Supercomputing Applications</A><br>
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+ at Urbana-Champaign</a><br>
+ <br>
+<!-- <A HREF="helpdesk.mail.html"> -->
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+hdfhelp@ncsa.uiuc.edu</A>
+<BR> <H6>Last Modified: August 27, 1999</H6><BR>
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