123 lines
6.4 KiB
HTML
123 lines
6.4 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1987-2016 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation. A copy of
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the license is included in the
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section entitled "GNU Free Documentation License".
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This manual contains no Invariant Sections. The Front-Cover Texts are
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(a) (see below), and the Back-Cover Texts are (b) (see below).
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>The C Preprocessor: Macros</title>
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<meta name="description" content="The C Preprocessor: Macros">
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<meta name="keywords" content="The C Preprocessor: Macros">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Index-of-Directives.html#Index-of-Directives" rel="index" title="Index of Directives">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="index.html#Top" rel="up" title="Top">
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<link href="Object_002dlike-Macros.html#Object_002dlike-Macros" rel="next" title="Object-like Macros">
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<link href="System-Headers.html#System-Headers" rel="prev" title="System Headers">
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Macros"></a>
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<div class="header">
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<p>
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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>
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</div>
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<hr>
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<a name="Macros-1"></a>
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<h2 class="chapter">3 Macros</h2>
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<p>A <em>macro</em> is a fragment of code which has been given a name.
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Whenever the name is used, it is replaced by the contents of the macro.
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There are two kinds of macros. They differ mostly in what they look
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like when they are used. <em>Object-like</em> macros resemble data objects
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when used, <em>function-like</em> macros resemble function calls.
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</p>
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<p>You may define any valid identifier as a macro, even if it is a C
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keyword. The preprocessor does not know anything about keywords. This
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can be useful if you wish to hide a keyword such as <code>const</code> from an
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older compiler that does not understand it. However, the preprocessor
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operator <code>defined</code> (see <a href="Defined.html#Defined">Defined</a>) can never be defined as a
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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
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macros when you are compiling C++.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Stringification.html#Stringification" accesskey="4">Stringification</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Concatenation.html#Concatenation" accesskey="5">Concatenation</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Macro-Pitfalls.html#Macro-Pitfalls">Macro Pitfalls</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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</table>
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</body>
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</html>
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