You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
127 lines
6.4 KiB
HTML
127 lines
6.4 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- Copyright (C) 1987-2018 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. A copy of
|
|
the license is included in the
|
|
section entitled "GNU Free Documentation License".
|
|
|
|
This manual contains no Invariant Sections. The Front-Cover Texts are
|
|
(a) (see below), and the Back-Cover Texts are (b) (see below).
|
|
|
|
(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 6.4, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<title>System-specific Predefined Macros (The C Preprocessor)</title>
|
|
|
|
<meta name="description" content="System-specific Predefined Macros (The C Preprocessor)">
|
|
<meta name="keywords" content="System-specific Predefined Macros (The C Preprocessor)">
|
|
<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="Index-of-Directives.html#Index-of-Directives" rel="index" title="Index of Directives">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="Predefined-Macros.html#Predefined-Macros" rel="up" title="Predefined Macros">
|
|
<link href="C_002b_002b-Named-Operators.html#C_002b_002b-Named-Operators" rel="next" title="C++ Named Operators">
|
|
<link href="Common-Predefined-Macros.html#Common-Predefined-Macros" rel="prev" title="Common Predefined Macros">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.indentedblock {margin-right: 0em}
|
|
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
|
|
blockquote.smallquotation {font-size: smaller}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
div.smalldisplay {margin-left: 3.2em}
|
|
div.smallexample {margin-left: 3.2em}
|
|
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.nolinebreak {white-space: nowrap}
|
|
span.roman {font-family: initial; font-weight: normal}
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<a name="System_002dspecific-Predefined-Macros"></a>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="C_002b_002b-Named-Operators.html#C_002b_002b-Named-Operators" accesskey="n" rel="next">C++ Named Operators</a>, Previous: <a href="Common-Predefined-Macros.html#Common-Predefined-Macros" accesskey="p" rel="prev">Common Predefined Macros</a>, Up: <a href="Predefined-Macros.html#Predefined-Macros" accesskey="u" rel="up">Predefined Macros</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
<hr>
|
|
<a name="System_002dspecific-Predefined-Macros-1"></a>
|
|
<h4 class="subsection">3.7.3 System-specific Predefined Macros</h4>
|
|
|
|
<a name="index-system_002dspecific-predefined-macros"></a>
|
|
<a name="index-predefined-macros_002c-system_002dspecific"></a>
|
|
<a name="index-reserved-namespace"></a>
|
|
|
|
<p>The C preprocessor normally predefines several macros that indicate what
|
|
type of system and machine is in use. They are obviously different on
|
|
each target supported by GCC. This manual, being for all systems and
|
|
machines, cannot tell you what their names are, but you can use
|
|
<code>cpp -dM</code> to see them all. See <a href="Invocation.html#Invocation">Invocation</a>. All system-specific
|
|
predefined macros expand to a constant value, so you can test them with
|
|
either ‘<samp>#ifdef</samp>’ or ‘<samp>#if</samp>’.
|
|
</p>
|
|
<p>The C standard requires that all system-specific macros be part of the
|
|
<em>reserved namespace</em>. All names which begin with two underscores,
|
|
or an underscore and a capital letter, are reserved for the compiler and
|
|
library to use as they wish. However, historically system-specific
|
|
macros have had names with no special prefix; for instance, it is common
|
|
to find <code>unix</code> defined on Unix systems. For all such macros, GCC
|
|
provides a parallel macro with two underscores added at the beginning
|
|
and the end. If <code>unix</code> is defined, <code>__unix__</code> will be defined
|
|
too. There will never be more than two underscores; the parallel of
|
|
<code>_mips</code> is <code>__mips__</code>.
|
|
</p>
|
|
<p>When the <samp>-ansi</samp> option, or any <samp>-std</samp> option that
|
|
requests strict conformance, is given to the compiler, all the
|
|
system-specific predefined macros outside the reserved namespace are
|
|
suppressed. The parallel macros, inside the reserved namespace, remain
|
|
defined.
|
|
</p>
|
|
<p>We are slowly phasing out all predefined macros which are outside the
|
|
reserved namespace. You should never use them in new programs, and we
|
|
encourage you to correct older code to use the parallel macros whenever
|
|
you find it. We don’t recommend you use the system-specific macros that
|
|
are in the reserved namespace, either. It is better in the long run to
|
|
check specifically for features you need, using a tool such as
|
|
<code>autoconf</code>.
|
|
</p>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="C_002b_002b-Named-Operators.html#C_002b_002b-Named-Operators" accesskey="n" rel="next">C++ Named Operators</a>, Previous: <a href="Common-Predefined-Macros.html#Common-Predefined-Macros" accesskey="p" rel="prev">Common Predefined Macros</a>, Up: <a href="Predefined-Macros.html#Predefined-Macros" accesskey="u" rel="up">Predefined Macros</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|