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203 lines
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203 lines
5.6 KiB
HTML
<HTML><HEAD>
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<TITLE>HDF5 Tutorial - Creating a Group
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</TITLE>
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</HEAD>
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<body bgcolor="#ffffff">
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<!-- BEGIN MAIN BODY -->
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[ <A HREF="title.html"><I>HDF5 Tutorial Top</I></A> ]
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<H1>
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<BIG><BIG><BIG><FONT COLOR="#c101cd">Creating a Group</FONT>
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</BIG></BIG></BIG></H1>
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<hr noshade size=1>
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<BODY>
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<H2>Contents:</H2>
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<UL>
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<LI> <A HREF="#def">What is a Group</A>?
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<LI> Programming Example
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<UL>
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<LI> <A HREF="#desc">Description</A>
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<LI> <A HREF="#rem">Remarks</A>
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<LI> <A HREF="#fc">File Contents</A>
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</UL>
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</UL>
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<HR>
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<A NAME="def">
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<H2>What is a Group?</h2>
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<P>
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An HDF5 group is a structure containing zero or more HDF5 objects. The two
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primary HDF5 objects are groups and datasets. To create a group, the calling
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program must:
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<OL>
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<LI> Obtain the location identifier where the group is to be created.
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<LI> Create the group.
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<LI> Close the group.
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</OL>
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To create a group, the calling program must call
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<code>H5Gcreate</code>/<code>h5gcreate_f</code>.
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To close the group, <code>H5Gclose</code>/<code>h5gclose_f</code>
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must be called. For example:
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<P>
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<I>C:</I>
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<PRE>
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group_id = H5Gcreate (loc_id, name, size_hint);
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status = H5Gclose (group_id);
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</PRE>
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<I>FORTRAN:</I>
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<PRE>
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CALL h5gcreate_f (loc_id, name, group_id, error, size_hint=size)
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<i>or</i>
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CALL h5gcreate_f (loc_id, name, group_id, error)
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CALL h5gclose_f (group_id, error)
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</PRE>
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<P>
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<H2> Programming Example</H2>
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<A NAME="desc">
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<H3><U>Description</U></H3>
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The following example shows how to create and close a group. It creates a file
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called <code>group.h5</code> (<code>groupf.h5</code> for FORTRAN),
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creates a group called <code>MyGroup</code> in the root group,
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and then closes the group and file. <BR>
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<UL>
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[ <A HREF="examples/h5_crtgrp.c">C Example</A> ]
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- <code>h5_crtgrp.c</code><BR>
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[ <A HREF="examples/groupexample.f90">FORTRAN Example</A> ]
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- <code>groupexample.f90</code><BR>
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[ <A HREF="examples/java/CreateGroup.java">Java Example</A> ]
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- <code>CreateGroup.java</code>
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</UL>
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<B>NOTE:</B> To download a tar file of the examples, including a Makefile,
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please go to the <A HREF="references.html">References</A> page.
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</PRE>
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<A NAME="rem">
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<H3><U>Remarks</U></H3>
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<UL>
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<LI><code>H5Gcreate</code>/<code>h5gcreate_f</code> creates
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a new empty group, named <code>MyGroup</code> and located in the
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root group, and returns a group identifier.
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<P>
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<I>C:</I>
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<PRE>
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hid_t H5Gcreate (hid_t loc_id, const char *name, size_t size_hint)
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</PRE>
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<I>FORTRAN:</I>
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<PRE>
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h5gcreate_f (loc_id, name, group_id, hdferr, size_hint)
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loc_id INTEGER(HID_T)
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name CHARACTER(LEN=*)
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group_id INTEGER(HID_T)
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hdferr INTEGER
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(Possible values: 0 on success and -1 on failure)
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size_hint INTEGER(SIZE_T), OPTIONAL
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(Default value: OBJECT_NAMELEN_DEFAULT_F)
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</PRE>
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<UL>
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<LI>The <I>loc_id</I> parameter specifies the location at which
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to create the group.
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<P>
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<LI> The <I>name</I> parameter specifies the name of the group to be created.
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<P>
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<LI> The <I>size_hint</I> parameter specifies how much file space to
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reserve to store the
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names that will appear in the group. If a non-positive value is supplied,
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then a default size is used. Passing a value of zero is usually adequate
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since the library is able to dynamically resize the name heap.
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<P>
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<LI>In FORTRAN, the return value for the routine is passed in
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<I>hdferr</I>: 0 if successful, -1 otherwise. The group identifier
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is passed back in <I>group_id</I>. In C, the function returns a valid
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group identifier if successful and a negative value otherwise.
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</UL>
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<P>
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<LI><code>H5Gclose</code>/<code>h5gclose_f</code> closes the group.
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This call is mandatory.
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<P>
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<I>C:</I>
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<PRE>
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herr_t H5Gclose (hid_t group_id)
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</PRE>
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<I>FORTRAN:</I>
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<PRE>
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h5gclose_f (group_id, hdferr)
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group_id INTEGER(HID_T)
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hdferr INTEGER
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(Possible values: 0 on success and -1 on failure)
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</PRE>
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</UL>
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<A NAME="fc">
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<H3><U>File Contents</U></H3>
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The contents of <code>group.h5</code> and the
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definition of the group are shown below. (The FORTRAN program
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creates the HDF5 file <code>groupf.h5</code> and the resulting DDL shows
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<code>groupf.h5</code> in the first line.)
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<P>
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<table width="80%" border="1" bordercolor="#FFFFFF" cellpadding="6" cellspacing="6">
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<tr valign=top>
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<td width="43%"><b>Fig. 8.1</b> <i>The Contents of <code>group.h5</code>.</i>
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</td>
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<td width="10%">
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</td>
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<td width="47%"><b>Fig. 8.2</b> <i><code>group.h5</code> in DDL</i> </td>
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</tr>
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<tr bordercolor="#000000">
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<!-- <td width="47%"><IMG src="grouph5.jpg" width="205" height="333"></td> -->
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<td align=center><IMG src="img003.gif"></td>
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<td bordercolor="#FFFFFF"> </td>
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<td valign="top">
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<pre>
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HDF5 "group.h5" {
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GROUP "/" {
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GROUP "MyGroup" {
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}
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}
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}
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</pre>
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</td>
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</tr>
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</table>
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<!-- BEGIN FOOTER INFO -->
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<P><hr noshade size=1>
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<font face="arial,helvetica" size="-1">
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<a href="http://www.ncsa.uiuc.edu/"><img border=0
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src="footer-ncsalogo.gif"
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width=78 height=27 alt="NCSA"><br>
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The National Center for Supercomputing Applications</A><br>
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<a href="http://www.uiuc.edu/">University of Illinois
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at Urbana-Champaign</a><br>
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<br>
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<!-- <A HREF="helpdesk.mail.html"> -->
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<A HREF="mailto:hdfhelp@ncsa.uiuc.edu">
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hdfhelp@ncsa.uiuc.edu</A>
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<br>
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<BR> <H6>Last Modified: June 22, 2001</H6><BR>
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<!-- modified by Barbara Jones - bljones@ncsa.uiuc.edu -->
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</FONT>
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<BR>
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