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Purpose:
    Adding Tutorial to development branch (R 1.4)
Platforms tested:
    IE 5
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Frank Baker
2000-12-22 15:47:59 -05:00
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<HTML><HEAD>
<TITLE>HDF5 Tutorial - Creating Groups using Absolute/Relative Names
</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">Creating Groups using
Absolute/Relative Names</FONT>
</BIG></BIG></BIG></H1>
<hr noshade size=1>
<BODY>
<H2>Contents:</H2>
<UL>
<LI> <A HREF="#def">Absolute vs. Relative Names</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>Absolute vs. Relative Names</h2>
<P>
Recall that to create an HDF5 object, we have to specify the location where the
object is to be created. This location is determined by the identifier of an HDF5
object and the name of the object to be created. The name of the created
object can be either an absolute name or a name relative to the specified
identifier.
In Example 5, we used the file identifier and the absolute name "/MyGroup" to create a
group. The file identifier and the name "/" specifies the location where the group
"MyGroup" was created.
<P>
In this section, we discuss HDF5 names and show how to use absolute/relative
names by giving an example of creating groups in a file.
<H3>Names</H3>
HDF5 object names are a slash-separated list of components. There are few
restrictions on names: component names may be any length except zero and may
contain any character except slash ("/") and the null terminator. A full name
may be composed of any number of component names separated by slashes, with any
of the component names being the special name ".". A name which begins with a
slash is an absolute name which is accessed beginning with the root group of the
file while all other relative names are accessed beginning with the specified
group. Multiple consecutive slashes in a full name are treated as single slashes
and trailing slashes are not significant. A special case is the name "/" (or
equivalent) which refers to the root group.
<P>
Functions which operate on names generally take a location identifier which
is either a file ID or a group ID and perform the lookup with respect to that
location. Some possibilities are:
<table width="67%" border="1" bordercolor="#000000" cellpadding="4">
<tr bgcolor="#ffcc99" bordercolor="#FFFFFF">
<td><b> Location Type </b></td>
<td><b>Object Name</b></td>
<td><b>Description</b></td>
</tr>
<tr bordercolor="#FFFFFF">
<td bgcolor="#99cccc" height="22">File ID</td>
<td height="22" bgcolor="#CCCCCC">
<div align="center">/foo/bar</div>
</td>
<td height="22">The object bar in group foo in the root group. </td>
</tr>
<tr bordercolor="#FFFFFF">
<td bgcolor="#99cccc">Group ID </td>
<td bgcolor="#CCCCCC">
<div align="center">/foo/bar</div>
</td>
<td>The object bar in group foo in the root group of the file containing the
specified group. In other words, the group ID's only purpose is to supply
a file. </td>
</tr>
<tr bordercolor="#FFFFFF">
<td bgcolor="#99cccc">File ID</td>
<td bgcolor="#CCCCCC">
<div align="center">/</div>
</td>
<td>The root group of the specified file.</td>
</tr>
<tr bordercolor="#FFFFFF">
<td bgcolor="#99cccc">Group ID</td>
<td bgcolor="#CCCCCC">
<div align="center">/</div>
</td>
<td>The root group of the file containing the specified group.</td>
</tr>
<tr bordercolor="#FFFFFF">
<td bgcolor="#99cccc">Group ID</td>
<td bgcolor="#CCCCCC">
<div align="center">foo/bar</div>
</td>
<td>The object bar in group foo in the specified group.</td>
</tr>
<tr bordercolor="#FFFFFF">
<td bgcolor="#99cccc">File ID</td>
<td bgcolor="#CCCCCC">
<div align="center">.</div>
</td>
<td>The root group of the file.</td>
</tr>
<tr bordercolor="#FFFFFF">
<td bgcolor="#99cccc">Group ID</td>
<td bgcolor="#CCCCCC">
<div align="center">.</div>
</td>
<td>The specified group.</td>
</tr>
<tr bordercolor="#FFFFFF">
<td bgcolor="#99cccc">Other ID</td>
<td bgcolor="#CCCCCC">
<div align="center">.</div>
</td>
<td>The specified object.</td>
</tr>
</table>
<P>
<H2> Programming Example</H2>
<A NAME="desc">
<H3><U>Description</U></H3>
The following example code shows how to create groups using absolute
and relative names. It creates three groups: the first two groups are
created using the file identifier and the group absolute names, and the
third group is created using a group identifier and the name relative
to the specified group. <BR>
[ <A HREF="examples/h5_crtgrpar.c">Download h5_crtgrpar.c</A> ]
<PRE>
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
#include &lt;hdf5.h&gt;
#define FILE "groups.h5"
main() {
hid_t file_id, group1_id, group2_id, group3_id; /* identifiers */
herr_t status;
/* Create a new file using default properties. */
file_id = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
/* Create group "MyGroup" in the root group using absolute name. */
group1_id = H5Gcreate(file_id, "/MyGroup", 0);
/* Create group "Group_A" in group "MyGroup" using absolute name. */
group2_id = H5Gcreate(file_id, "/MyGroup/Group_A", 0);
/* Create group "Group_B" in group "MyGroup" using relative name. */
group3_id = H5Gcreate(group1_id, "Group_B", 0);
/* Close groups. */
status = H5Gclose(group1_id);
status = H5Gclose(group2_id);
status = H5Gclose(group3_id);
/* Close the file. */
status = H5Fclose(file_id);
}
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
</PRE>
<A NAME="rem">
<H3><U>Remarks</U></H3>
<UL>
<LI> H5Gcreate creates a group at the location specified by a location ID and a
name. The location ID can be a file ID or a group ID and the name can be
relative or absolute.
<LI> The first H5Gcreate creates the group 'MyGroup' in the root group of the
specified file.
<LI> The second H5Gcreate creates the group 'Group_A' in the group 'MyGroup'
in the root group of the specified file. Note that the parent group (MyGroup)
already exists.
<LI> The third H5Gcreate creates the group 'Group_B' in the specified group.
</UL>
<A NAME="fc">
<H3><U>File Contents</U></H3>
The file contents are shown below:
<P>
<B>Fig. 9.1</B> &nbsp; <I>The Contents of 'groups.h5'</I>
<P>
<!--<IMG src="groupsh5.jpg" width="285" height="383"></P> -->
<IMG src="img004.gif"></P>
<B> Fig. 9.2</B> &nbsp; <I>'groups.h5' in DDL</I>
<PRE>
HDF5 "groups.h5" {
GROUP "/" {
GROUP "MyGroup" {
GROUP "Group_A" {
}
GROUP "Group_B" {
}
}
}
}
</PRE>
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The National Center for Supercomputing Applications</A><br>
<a href="http://www.uiuc.edu/">University of Illinois
at Urbana-Champaign</a><br>
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<BR> <H6>Last Modified: August 27, 1999</H6><BR>
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