<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
<html>
|
<!-- Copyright (C) 1999-2016 Free Software Foundation, Inc.
|
|
Permission is granted to copy, distribute and/or modify this document
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
any later version published by the Free Software Foundation; with the
|
Invariant Sections being "Funding Free Software", the Front-Cover
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
(see below). A copy of the license is included in the section entitled
|
"GNU Free Documentation License".
|
|
(a) The FSF's Front-Cover Text is:
|
|
A GNU Manual
|
|
(b) The FSF's Back-Cover Text is:
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
software. Copies published by the Free Software Foundation raise
|
funds for GNU development. -->
|
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
|
<head>
|
<title>The GNU Fortran Compiler: CONVERT specifier</title>
|
|
<meta name="description" content="The GNU Fortran Compiler: CONVERT specifier">
|
<meta name="keywords" content="The GNU Fortran Compiler: CONVERT specifier">
|
<meta name="resource-type" content="document">
|
<meta name="distribution" content="global">
|
<meta name="Generator" content="makeinfo">
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
<link href="index.html#Top" rel="start" title="Top">
|
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
<link href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" rel="up" title="Extensions implemented in GNU Fortran">
|
<link href="OpenMP.html#OpenMP" rel="next" title="OpenMP">
|
<link href="Cray-pointers.html#Cray-pointers" rel="prev" title="Cray pointers">
|
<style type="text/css">
|
<!--
|
a.summary-letter {text-decoration: none}
|
blockquote.smallquotation {font-size: smaller}
|
div.display {margin-left: 3.2em}
|
div.example {margin-left: 3.2em}
|
div.indentedblock {margin-left: 3.2em}
|
div.lisp {margin-left: 3.2em}
|
div.smalldisplay {margin-left: 3.2em}
|
div.smallexample {margin-left: 3.2em}
|
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
|
div.smalllisp {margin-left: 3.2em}
|
kbd {font-style:oblique}
|
pre.display {font-family: inherit}
|
pre.format {font-family: inherit}
|
pre.menu-comment {font-family: serif}
|
pre.menu-preformatted {font-family: serif}
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
pre.smallexample {font-size: smaller}
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
pre.smalllisp {font-size: smaller}
|
span.nocodebreak {white-space:nowrap}
|
span.nolinebreak {white-space:nowrap}
|
span.roman {font-family:serif; font-weight:normal}
|
span.sansserif {font-family:sans-serif; font-weight:normal}
|
ul.no-bullet {list-style: none}
|
-->
|
</style>
|
|
|
</head>
|
|
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
|
<a name="CONVERT-specifier"></a>
|
<div class="header">
|
<p>
|
Next: <a href="OpenMP.html#OpenMP" accesskey="n" rel="next">OpenMP</a>, Previous: <a href="Cray-pointers.html#Cray-pointers" accesskey="p" rel="prev">Cray pointers</a>, Up: <a href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" accesskey="u" rel="up">Extensions implemented in GNU Fortran</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
|
</div>
|
<hr>
|
<a name="CONVERT-specifier-1"></a>
|
<h4 class="subsection">6.1.15 <code>CONVERT</code> specifier</h4>
|
<a name="index-CONVERT-specifier"></a>
|
|
<p>GNU Fortran allows the conversion of unformatted data between little-
|
and big-endian representation to facilitate moving of data
|
between different systems. The conversion can be indicated with
|
the <code>CONVERT</code> specifier on the <code>OPEN</code> statement.
|
See <a href="GFORTRAN_005fCONVERT_005fUNIT.html#GFORTRAN_005fCONVERT_005fUNIT">GFORTRAN_CONVERT_UNIT</a>, for an alternative way of specifying
|
the data format via an environment variable.
|
</p>
|
<p>Valid values for <code>CONVERT</code> are:
|
</p><ul class="no-bullet">
|
<li><!-- /@w --> <code>CONVERT='NATIVE'</code> Use the native format. This is the default.
|
</li><li><!-- /@w --> <code>CONVERT='SWAP'</code> Swap between little- and big-endian.
|
</li><li><!-- /@w --> <code>CONVERT='LITTLE_ENDIAN'</code> Use the little-endian representation
|
for unformatted files.
|
</li><li><!-- /@w --> <code>CONVERT='BIG_ENDIAN'</code> Use the big-endian representation for
|
unformatted files.
|
</li></ul>
|
|
<p>Using the option could look like this:
|
</p><div class="smallexample">
|
<pre class="smallexample"> open(file='big.dat',form='unformatted',access='sequential', &
|
convert='big_endian')
|
</pre></div>
|
|
<p>The value of the conversion can be queried by using
|
<code>INQUIRE(CONVERT=ch)</code>. The values returned are
|
<code>'BIG_ENDIAN'</code> and <code>'LITTLE_ENDIAN'</code>.
|
</p>
|
<p><code>CONVERT</code> works between big- and little-endian for
|
<code>INTEGER</code> values of all supported kinds and for <code>REAL</code>
|
on IEEE systems of kinds 4 and 8. Conversion between different
|
“extended double” types on different architectures such as
|
m68k and x86_64, which GNU Fortran
|
supports as <code>REAL(KIND=10)</code> and <code>REAL(KIND=16)</code>, will
|
probably not work.
|
</p>
|
<p><em>Note that the values specified via the GFORTRAN_CONVERT_UNIT
|
environment variable will override the CONVERT specifier in the
|
open statement</em>. This is to give control over data formats to
|
users who do not have the source code of their program available.
|
</p>
|
<p>Using anything but the native representation for unformatted data
|
carries a significant speed overhead. If speed in this area matters
|
to you, it is best if you use this only for data that needs to be
|
portable.
|
</p>
|
<hr>
|
<div class="header">
|
<p>
|
Next: <a href="OpenMP.html#OpenMP" accesskey="n" rel="next">OpenMP</a>, Previous: <a href="Cray-pointers.html#Cray-pointers" accesskey="p" rel="prev">Cray pointers</a>, Up: <a href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" accesskey="u" rel="up">Extensions implemented in GNU Fortran</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
|
</div>
|
|
|
|
</body>
|
</html>
|
