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<HTML><HEAD>
<TITLE>HDF5 Tutorial - Creating an HDF5 File
</TITLE>
</HEAD>
<body bgcolor="#ffffff">
<!-- BEGIN MAIN BODY -->
[ <A HREF="title.html"><I>HDF5 Tutorial Top</I></A> ]
<H1>
<BIG><BIG><BIG><FONT COLOR="#c101cd">Creating an HDF5 File</FONT>
</BIG></BIG></BIG></H1>
<hr noshade size=1>
<BODY>
<H2>Contents:</H2>
<UL>
<LI> <A HREF="#def">What is an HDF5 file</A>?
<LI>Programming Example
<UL>
<LI> <A HREF="#desc">Description</A>
<LI> <A HREF="#rem">Remarks</A>
<LI> <A HREF="#fc">File Contents</A>
<LI> <A HREF="#ddl">File Definition in DDL</A>
</UL>
</UL>
<HR>
<A NAME="def">
<H2>What is an HDF5 file?</h2>
<P>
An HDF5 file is a binary file containing scientific data and supporting
metadata. The primary types of objects stored in an HDF5 file, groups and
datasets, will be discussed in other sections of this tutorial.
<P>
To create a file, an application must specify a filename, file
access mode, file creation property list, and file access property list.
<P>
<UL>
<LI><B> File access mode:</B><BR>
When creating a file, the file access mode specifies the action to
take if the file already exists:
<UL>
<LI><code>H5F_ACC_TRUNC</code> specifies that if the file already exists,
the current contents will be deleted so that the application can rewrite
the file with new data.
<LI><code>H5F_ACC_EXCL</code> specifies that the open is to fail if
the file already exists.
<LI>If the file does not already exist, the file access parameter is
ignored.
<LI>In all cases, the application has both read and write access to
a successfully created file.
</UL>
<P>
Note that there are two different access modes for opening exisitng files:
<UL>
<LI><code>H5F_ACC_RDONLY</code> specifies that the application has
read access but will not be allowed to write any data.
<LI><code>H5F_ACC_RDWR</code> specifies that the application has
read and write access.
</UL>
<P>
For further information, see
<a href="../Files.html">The File Interface (H5F)</a> section of the
<cite>HDF5 User's Guide</cite> and
the <a href="../RM_H5F.html#File-Create">H5F: File Interface</a>
section of the <cite>HDF5 Reference Manual</cite>.
<P>
<LI><B> File creation property list:</B><BR>
The file creation property list is used to control the file metadata.
File metadata contains information about the size of the user-block, the
size of various file data structures used by the HDF5 library, etc.
In this tutorial, the default file creation property list,
<code>H5P_DEFAULT</code>, is used.
<P>
The user-block is a fixed-length block of data located at the beginning
of the file which is ignored by the HDF5 library.
The user-block may be used to store
any data or information found to be useful to applications.
<P>
For further information, see
<a href="../Files.html">The File Interface (H5F)</a> section of the
<cite>HDF5 User's Guide</cite>.
<P>
<LI><B> File access property list:</B><BR>
The file access property list is used to control different methods of
performing I/O on files.
The default file access property list, <code>H5P_DEFAULT</code>,
is used in this tutorial.
<P>
For further information, see
<a href="../Files.html">The File Interface (H5F)</a> section of the
<cite>HDF5 User's Guide</cite>.
</UL>
<P>
The steps to create and close an HDF5 file are as follows:
<OL>
<LI> Specify the file creation and access property lists, if necessary.
<LI> Create the file.
<LI> Close the file and close the property lists, if necessary.
</OL>
To create an HDF5 file, the calling program must contain calls to
create and close the file. For example:
<P>
<I>C</I>:<PRE>
file_id = H5Fcreate (filename, access_mode, create_id, access_id);
status = H5Fclose (file_id);
</PRE>
<I>FORTRAN</I>:<PRE>
CALL h5fcreate_f (filename, access_mode, file_id, hdferr, &
creation_prp=create_id, access_prp=access_id)
<i>or</i>
CALL h5fcreate_f (filename, access_mode, file_id, hdferr)
CALL h5fclose_f (file_id, hdferr)
</PRE>
In FORTRAN, the file creation property list, <code>creation_prp</code>,
and file access property list, <code>access_prp</code>,
are optional parameters;
they can be omitted if the default values are to be used.
<P>
<H2>Programming Example</H2>
<A NAME="desc">
<H3><U>Description</U></H3>
The following example demonstrates how to create and close an HDF5 file.
It creates a file called <code>file.h5</code> in the C version,
<code>filef.h5</code> in FORTRAN, and then closes the file.<P>
<UL>
[ <A HREF="examples/h5_crtfile.c" target="ExternalWin">C Example</A> ]
-- <code>h5_crtfile.c</code> <BR>
[ <A HREF="examples/fileexample.f90" target="ExternalWin">FORTRAN Example</A> ]
-- <code>fileexample.f90</code><BR>
[ <A HREF="examples/java/CreateFile.java" target="ExternalWin">Java Example</A> ] -- <code>CreateFile.java</code>
</UL>
<P>
<B>NOTE:</B> To download a tar file of all of the examples, including
a Makefile, please go to the <A HREF="references.html">References</A> page.
<A NAME="rem">
<H3><U>Remarks</U></H3>
<UL>
<LI><B>In C:</B>
The include file <code>hdf5.h</code> contains definitions and declarations
and must be included in any program that uses the HDF5 library.
<BR><B>In FORTRAN:</B>
The module <code>HDF5</code> contains definitions and declarations
and must be used in any program that uses the HDF5 library.
<P>
<LI><code>H5Fcreate</code>/<code>h5fcreate_f</code> creates
an HDF5 file and returns the file identifier.
<PRE>
<I>C</I>:
hid_t H5Fcreate (const char *name, unsigned access_mode, hid_t creation_prp,
hid_t access_prp)
<I>FORTRAN</I>:
h5fcreate_f (name, access_mode, file_id, hdferr, creation_prp, access_prp)
name CHARACTER(LEN=*)
access_flag INTEGER
(Valid values: H5F_ACC_RDWR_F, H5F_ACC_RDONLY_F,
H5F_ACC_TRUNC_F, H5F_ACC_EXCL_F, H5F_ACC_DEBUG_F)
file_id INTEGER(HID_T)
hdferr INTEGER
(Valid values: 0 on success and -1 on failure)
creation_prp INTEGER(HID_T), OPTIONAL
(Default value: H5P_DEFAULT_F)
access_prp INTEGER(HID_T), OPTIONAL
(Default value: H5P_DEFAULT_F)
</PRE>
<UL>
<LI> The <I>name</I> parameter specifies the name of the file to be created.
<P>
<LI> The <I>access_mode</I> parameter specifies the file access mode.
<code>H5F_ACC_TRUNC</code> (<code>H5F_ACC_TRUNC_F</code> in FORTRAN)
will truncate a file if it already exists.
<P>
<LI> The <I>creation_prp</I> parameter
specifies the file creation property list.
For C, using <code>H5P_DEFAULT</code> indicates that the
default file creation property list is to be used.
This option is optional in FORTRAN; if it is omitted, the default file
creation property list, <code>H5P_DEFAULT_F</code>, is used.
<P>
<LI> The <I>access_prp</I> parameter
specifies the file access property list.
For C, using <code>H5P_DEFAULT</code> indicates that the
default file creation property list is to be used.
This option is optional in FORTRAN; if it is omitted, the default file
creation property list, <code>H5P_DEFAULT_F</code>, is used.
<P>
<LI> In C, this function returns the file identifier if successful and
a negative value otherwise.
In FORTRAN, the file identifier is returned in the
<I>file_id</I> parameter. If the call is successful, 0 (zero) is
passed back in the <I>hdferr</I> parameter. Otherwise, <I>hdferr</I>
will have a value of -1.
</UL>
<P>
<LI> When a file is no longer accessed by a program,
<code>H5Fclose</code>/<code>h5fclose_f</code>
must be called to release the resources used by the file. This call
is mandatory.
<PRE>
<I>C</I>:
herr_t H5Fclose (hid_t file_id)
<I>FORTRAN</I>:
h5fclose_f(file_id, hdferr)
</PRE>
<P>
<LI>The root group is automatically created when a file is created.
Every file has a root group and the path name of the root group is
always <code>/</code>.
</UL>
<A NAME="fc">
<H3><U>File Contents</U></H3>
The HDF team has developed tools for examining the contents of HDF5 files.
The tool used in this tutorial is the HDF5 dumper, <code>h5dump</code>,
which displays the file contents in human-readable form.
The output of <code>h5dump</code> is an ASCII display formatted according
to the HDF5 DDL grammar.
This grammar is defined, using Backus-Naur Form, in the
<a href="../ddl.html">DDL in BNF for HDF5</a>.
<p>
To view the file contents, type:
<PRE>
<B>h5dump <filename></B>
</PRE>
Figure 4.1 describes the file contents of <code>file.h5</code> (<code>filef.h5</code>)
using a directed graph.
The directed graphs in this tutorial use an oval to represent an HDF5 group
and a rectangle to represent an HDF5 dataset (none in this example).
Arrows indicate the inclusion direction of the contents (none in this example).
<P>
<B>Fig. 4.1</B> <I>Contents of <code>file.h5</code> (<code>filef.h5</code>)</I>
<PRE>
<!--
<IMG src="fileh5.jpg" width="205" height="208"></PRE> -->
<IMG src="img001.gif"></PRE>
Figure 4.2 is the text description of <code>file.h5</code>, as generated by
<code>h5dump</code>. The HDF5 file called <code>file.h5</code> contains
a group called <code>/</code>, or the <I>root group</I>.
(The file called <code>filef.h5</code>,
created by the FORTRAN version of the example, has the same output except
that the filename shown is <code>filef.h5</code>.)
<P>
<B> Fig. 4.2</B> <I><code>file.h5</code> in DDL</I>
<PRE>
HDF5 "file.h5" {
GROUP "/" {
}
}
</PRE>
<A NAME="ddl">
<h3><U>File Definition in DDL</U></H3>
Figure 4.3 is the simplified DDL file definition for creating an HDF5 file.
For simplicity, a simplified DDL is used in this tutorial. A complete and
more rigorous DDL can be found in the
<a href="../ddl.html">DDL in BNF for HDF5</a>, a section of the
<cite>HDF5 User's Guide</cite>.
<P>
<B> Fig. 4.3</B> <I>HDF5 File Definition</I>
<P>
The following symbol definitions are used in the DDL:
<PRE>
::= defined as
<tname> a token with the name <I>tname</I>
<a> | <b> one of <a> or <b>
<a>* zero or more occurrences of <a>
</PRE>
The simplified DDL for file definition is as follows:
<PRE>
<file> ::= HDF5 "<file_name>" { <root_group> }
<root_group> ::= GROUP "/" { <group_attribute>* <group_member>* }
<group_attribute> ::= <attribute>
<group_member> ::= <group> | <dataset>
</PRE>
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<BR> <H6>Last Modified: June 22, 2001</H6><BR>
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