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.
122 lines
6.3 KiB
HTML
122 lines
6.3 KiB
HTML
4 years ago
|
<!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>Macros (The C Preprocessor)</title>
|
||
|
|
|
||
|
|
<meta name="description" content="Macros (The C Preprocessor)">
|
||
|
|
<meta name="keywords" content="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="index.html#Top" rel="up" title="Top">
|
||
|
|
<link href="Object_002dlike-Macros.html#Object_002dlike-Macros" rel="next" title="Object-like Macros">
|
||
|
|
<link href="System-Headers.html#System-Headers" rel="prev" title="System Headers">
|
||
|
|
<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="Macros"></a>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Conditionals.html#Conditionals" accesskey="n" rel="next">Conditionals</a>, Previous: <a href="Header-Files.html#Header-Files" accesskey="p" rel="prev">Header Files</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</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="Macros-1"></a>
|
||
|
|
<h2 class="chapter">3 Macros</h2>
|
||
|
|
|
||
|
|
<p>A <em>macro</em> is a fragment of code which has been given a name.
|
||
|
|
Whenever the name is used, it is replaced by the contents of the macro.
|
||
|
|
There are two kinds of macros. They differ mostly in what they look
|
||
|
|
like when they are used. <em>Object-like</em> macros resemble data objects
|
||
|
|
when used, <em>function-like</em> macros resemble function calls.
|
||
|
|
</p>
|
||
|
|
<p>You may define any valid identifier as a macro, even if it is a C
|
||
|
|
keyword. The preprocessor does not know anything about keywords. This
|
||
|
|
can be useful if you wish to hide a keyword such as <code>const</code> from an
|
||
|
|
older compiler that does not understand it. However, the preprocessor
|
||
|
|
operator <code>defined</code> (see <a href="Defined.html#Defined">Defined</a>) can never be defined as a
|
||
|
|
macro, and C++’s named operators (see <a href="C_002b_002b-Named-Operators.html#C_002b_002b-Named-Operators">C++ Named Operators</a>) cannot be
|
||
|
|
macros when you are compiling C++.
|
||
|
|
</p>
|
||
|
|
<table class="menu" border="0" cellspacing="0">
|
||
|
|
<tr><td align="left" valign="top">• <a href="Object_002dlike-Macros.html#Object_002dlike-Macros" accesskey="1">Object-like Macros</a>:</td><td> </td><td align="left" valign="top">
|
||
|
|
</td></tr>
|
||
|
|
<tr><td align="left" valign="top">• <a href="Function_002dlike-Macros.html#Function_002dlike-Macros" accesskey="2">Function-like Macros</a>:</td><td> </td><td align="left" valign="top">
|
||
|
|
</td></tr>
|
||
|
|
<tr><td align="left" valign="top">• <a href="Macro-Arguments.html#Macro-Arguments" accesskey="3">Macro Arguments</a>:</td><td> </td><td align="left" valign="top">
|
||
|
|
</td></tr>
|
||
|
|
<tr><td align="left" valign="top">• <a href="Stringizing.html#Stringizing" accesskey="4">Stringizing</a>:</td><td> </td><td align="left" valign="top">
|
||
|
|
</td></tr>
|
||
|
|
<tr><td align="left" valign="top">• <a href="Concatenation.html#Concatenation" accesskey="5">Concatenation</a>:</td><td> </td><td align="left" valign="top">
|
||
|
|
</td></tr>
|
||
|
|
<tr><td align="left" valign="top">• <a href="Variadic-Macros.html#Variadic-Macros" accesskey="6">Variadic Macros</a>:</td><td> </td><td align="left" valign="top">
|
||
|
|
</td></tr>
|
||
|
|
<tr><td align="left" valign="top">• <a href="Predefined-Macros.html#Predefined-Macros" accesskey="7">Predefined Macros</a>:</td><td> </td><td align="left" valign="top">
|
||
|
|
</td></tr>
|
||
|
|
<tr><td align="left" valign="top">• <a href="Undefining-and-Redefining-Macros.html#Undefining-and-Redefining-Macros" accesskey="8">Undefining and Redefining Macros</a>:</td><td> </td><td align="left" valign="top">
|
||
|
|
</td></tr>
|
||
|
|
<tr><td align="left" valign="top">• <a href="Directives-Within-Macro-Arguments.html#Directives-Within-Macro-Arguments" accesskey="9">Directives Within Macro Arguments</a>:</td><td> </td><td align="left" valign="top">
|
||
|
|
</td></tr>
|
||
|
|
<tr><td align="left" valign="top">• <a href="Macro-Pitfalls.html#Macro-Pitfalls">Macro Pitfalls</a>:</td><td> </td><td align="left" valign="top">
|
||
|
|
</td></tr>
|
||
|
|
</table>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|