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<HTML><HEAD>
<TITLE>HDF5 Tutorial - Creating a Group
</TITLE>
</HEAD>
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[ <A HREF="title.html"><I>HDF5 Tutorial Top</I></A> ]
<H1>
<BIG><BIG><BIG><FONT COLOR="#c101cd">Creating a Group</FONT>
</BIG></BIG></BIG></H1>
<hr noshade size=1>
<BODY>
<H2>Contents:</H2>
<UL>
<LI> <A HREF="#def">What is a Group</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>What is a Group?</h2>
<P>
An HDF5 group is a structure containing zero or more HDF5 objects. The two
primary HDF5 objects are groups and datasets. To create a group, the calling
program must:
<OL>
<LI> Obtain the location identifier where the group is to be created.
<LI> Create the group.
<LI> Close the group.
</OL>
To create a group, the calling program must contain the following calls:
<PRE>
group_id = H5Gcreate (loc_id, name, size_hint);
H5Gclose (group_id);
</PRE>
<P>
<H2> Programming Example</H2>
<A NAME="desc">
<H3><U>Description</U></H3>
The following example shows how to create and close a group. It creates a file
called 'group.h5', creates a group called <I>MyGroup</I> in the root group,
and then closes the group and file. <BR>
[ <A HREF="examples/h5_crtgrp.c">Download h5_crtgrp.c</A> ]
<PRE>
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
#include <hdf5.h>
#define FILE "group.h5"
main() {
hid_t file_id, group_id; /* identifiers */
herr_t status;
/* Create a new file using default properties. */
file_id = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
/* Create a group named "/MyGroup" in the file. */
group_id = H5Gcreate(file_id, "/MyGroup", 0);
/* Close the group. */
status = H5Gclose(group_id);
/* Terminate access to the file. */
status = H5Fclose(file_id);
}
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
</PRE>
<A NAME="rem">
<H3><U>Remarks</U></H3>
<UL>
<LI> H5Gcreate creates a new empty group and returns a group identifier.
<PRE>
hid_t H5Gcreate (hid_t loc_id, const char *name, size_t size_hint)
</PRE>
<UL>
<LI> The first parameter specifies the location to create the group.
<LI> The second parameter specifies the name of the group to be created.
<LI> The third parameter specifies how much file space to reserve to store the
names that will appear in the group. If a non-positive value is supplied,
then a default size is used. Passing a value of zero is usually adequate
since the library is able to dynamically resize the name heap.
</UL>
<P>
<LI> H5Gcreate creates a group named <I>MyGroup</I> in the root group of the specified
file.
<P>
<LI> H5Gclose closes the group. This call is mandatory.
<PRE>
herr_t H5Gclose (hid_t group_id)
</PRE>
</UL>
<A NAME="fc">
<H3><U>File Contents</U></H3>
The contents of 'group.h5' and the definition of the group are given in the
following:
<P>
<table width="56%" border="1" bordercolor="#FFFFFF" cellpadding="6" cellspacing="6">
<tr>
<td width="47%"><b>Fig. 8.1</b> <i>The Contents of 'group.h5'.</i>
</td>
<td width="53%"><b>Fig. 8.2</b> <i>'group.h5' in DDL</i> </td>
</tr>
<tr bordercolor="#000000">
<!-- <td width="47%"><IMG src="grouph5.jpg" width="205" height="333"></td> -->
<td width="47%"><IMG src="img003.gif"></td>
<td width="53%" valign="top">
<pre>
HDF5 "group.h5" {
GROUP "/" {
GROUP "MyGroup" {
}
}
}
</pre>
</td>
</tr>
</table>
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The National Center for Supercomputing Applications</A><br>
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<BR> <H6>Last Modified: August 27, 1999</H6><BR>
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