| 1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|---|
| 2 | <html>
|
|---|
| 3 | <!-- Copyright (C) 2022 Richard Stallman and Free Software Foundation, Inc.
|
|---|
| 4 |
|
|---|
| 5 | (The work of Trevis Rothwell and Nelson Beebe has been assigned or
|
|---|
| 6 | licensed to the FSF.)
|
|---|
| 7 |
|
|---|
| 8 | Permission is granted to copy, distribute and/or modify this document
|
|---|
| 9 | under the terms of the GNU Free Documentation License, Version 1.3 or
|
|---|
| 10 | any later version published by the Free Software Foundation; with the
|
|---|
| 11 | Invariant Sections being "GNU General Public License," with the
|
|---|
| 12 | Front-Cover Texts being "A GNU Manual," and with the Back-Cover
|
|---|
| 13 | Texts as in (a) below. A copy of the license is included in the
|
|---|
| 14 | section entitled "GNU Free Documentation License."
|
|---|
| 15 |
|
|---|
| 16 | (a) The FSF's Back-Cover Text is: "You have the freedom to copy and
|
|---|
| 17 | modify this GNU manual. Buying copies from the FSF supports it in
|
|---|
| 18 | developing GNU and promoting software freedom." -->
|
|---|
| 19 | <!-- Created by GNU Texinfo 6.7, http://www.gnu.org/software/texinfo/ -->
|
|---|
| 20 | <head>
|
|---|
| 21 | <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|---|
| 22 | <title>Macros (GNU C Language Manual)</title>
|
|---|
| 23 |
|
|---|
| 24 | <meta name="description" content="Macros (GNU C Language Manual)">
|
|---|
| 25 | <meta name="keywords" content="Macros (GNU C Language Manual)">
|
|---|
| 26 | <meta name="resource-type" content="document">
|
|---|
| 27 | <meta name="distribution" content="global">
|
|---|
| 28 | <meta name="Generator" content="makeinfo">
|
|---|
| 29 | <link href="index.html" rel="start" title="Top">
|
|---|
| 30 | <link href="Symbol-Index.html" rel="index" title="Symbol Index">
|
|---|
| 31 | <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|---|
| 32 | <link href="Preprocessing.html" rel="up" title="Preprocessing">
|
|---|
| 33 | <link href="Object_002dlike-Macros.html" rel="next" title="Object-like Macros">
|
|---|
| 34 | <link href="Computed-Includes.html" rel="prev" title="Computed Includes">
|
|---|
| 35 | <style type="text/css">
|
|---|
| 36 | <!--
|
|---|
| 37 | a.summary-letter {text-decoration: none}
|
|---|
| 38 | blockquote.indentedblock {margin-right: 0em}
|
|---|
| 39 | div.display {margin-left: 3.2em}
|
|---|
| 40 | div.example {margin-left: 3.2em}
|
|---|
| 41 | div.lisp {margin-left: 3.2em}
|
|---|
| 42 | kbd {font-style: oblique}
|
|---|
| 43 | pre.display {font-family: inherit}
|
|---|
| 44 | pre.format {font-family: inherit}
|
|---|
| 45 | pre.menu-comment {font-family: serif}
|
|---|
| 46 | pre.menu-preformatted {font-family: serif}
|
|---|
| 47 | span.nolinebreak {white-space: nowrap}
|
|---|
| 48 | span.roman {font-family: initial; font-weight: normal}
|
|---|
| 49 | span.sansserif {font-family: sans-serif; font-weight: normal}
|
|---|
| 50 | ul.no-bullet {list-style: none}
|
|---|
| 51 | -->
|
|---|
| 52 | </style>
|
|---|
| 53 |
|
|---|
| 54 |
|
|---|
| 55 | </head>
|
|---|
| 56 |
|
|---|
| 57 | <body lang="en">
|
|---|
| 58 | <span id="Macros"></span><div class="header">
|
|---|
| 59 | <p>
|
|---|
| 60 | Next: <a href="Conditionals.html" accesskey="n" rel="next">Conditionals</a>, Previous: <a href="Header-Files.html" accesskey="p" rel="prev">Header Files</a>, Up: <a href="Preprocessing.html" accesskey="u" rel="up">Preprocessing</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Index.html" title="Index" rel="index">Index</a>]</p>
|
|---|
| 61 | </div>
|
|---|
| 62 | <hr>
|
|---|
| 63 | <span id="Macros-1"></span><h3 class="section">26.5 Macros</h3>
|
|---|
| 64 | <span id="index-macros"></span>
|
|---|
| 65 |
|
|---|
| 66 | <p>A <em>macro</em> is a fragment of code that has been given a name.
|
|---|
| 67 | Whenever the name is used, it is replaced by the contents of the macro.
|
|---|
| 68 | There are two kinds of macros. They differ mostly in what they look
|
|---|
| 69 | like when they are used. <em>Object-like</em> macros resemble data objects
|
|---|
| 70 | when used, <em>function-like</em> macros resemble function calls.
|
|---|
| 71 | </p>
|
|---|
| 72 | <p>You may define any valid identifier as a macro, even if it is a C
|
|---|
| 73 | keyword. In the preprocessing stage, GCC does not know anything about
|
|---|
| 74 | keywords. This can be useful if you wish to hide a keyword such as
|
|---|
| 75 | <code>const</code> from an older compiler that does not understand it.
|
|---|
| 76 | However, the preprocessing operator <code>defined</code> (see <a href="defined.html">defined</a>)
|
|---|
| 77 | can never be defined as a macro, and C<code>++</code>’s named operators
|
|---|
| 78 | (see <a href="https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Named-Operators.html#C_002b_002b-Named-Operators">C++ Named Operators</a> in <cite>Using the GNU Compiler Collection</cite>) cannot be macros when
|
|---|
| 79 | compiling C<code>++</code> code.
|
|---|
| 80 | </p>
|
|---|
| 81 | <p>The operator <code>#</code> is used in macros for stringification of an
|
|---|
| 82 | argument (see <a href="Stringification.html">Stringification</a>), and <code>##</code> is used for
|
|---|
| 83 | concatenation of arguments into larger tokens (see <a href="Concatenation.html">Concatenation</a>)
|
|---|
| 84 | </p>
|
|---|
| 85 | <table class="menu" border="0" cellspacing="0">
|
|---|
| 86 | <tr><td align="left" valign="top">• <a href="Object_002dlike-Macros.html" accesskey="1">Object-like Macros</a></td><td> </td><td align="left" valign="top">
|
|---|
| 87 | </td></tr>
|
|---|
| 88 | <tr><td align="left" valign="top">• <a href="Function_002dlike-Macros.html" accesskey="2">Function-like Macros</a></td><td> </td><td align="left" valign="top">
|
|---|
| 89 | </td></tr>
|
|---|
| 90 | <tr><td align="left" valign="top">• <a href="Macro-Arguments.html" accesskey="3">Macro Arguments</a></td><td> </td><td align="left" valign="top">
|
|---|
| 91 | </td></tr>
|
|---|
| 92 | <tr><td align="left" valign="top">• <a href="Stringification.html" accesskey="4">Stringification</a></td><td> </td><td align="left" valign="top">
|
|---|
| 93 | </td></tr>
|
|---|
| 94 | <tr><td align="left" valign="top">• <a href="Concatenation.html" accesskey="5">Concatenation</a></td><td> </td><td align="left" valign="top">
|
|---|
| 95 | </td></tr>
|
|---|
| 96 | <tr><td align="left" valign="top">• <a href="Variadic-Macros.html" accesskey="6">Variadic Macros</a></td><td> </td><td align="left" valign="top">
|
|---|
| 97 | </td></tr>
|
|---|
| 98 | <tr><td align="left" valign="top">• <a href="Predefined-Macros.html" accesskey="7">Predefined Macros</a></td><td> </td><td align="left" valign="top">
|
|---|
| 99 | </td></tr>
|
|---|
| 100 | <tr><td align="left" valign="top">• <a href="Undefining-and-Redefining-Macros.html" accesskey="8">Undefining and Redefining Macros</a></td><td> </td><td align="left" valign="top">
|
|---|
| 101 | </td></tr>
|
|---|
| 102 | <tr><td align="left" valign="top">• <a href="Directives-Within-Macro-Arguments.html" accesskey="9">Directives Within Macro Arguments</a></td><td> </td><td align="left" valign="top">
|
|---|
| 103 | </td></tr>
|
|---|
| 104 | <tr><td align="left" valign="top">• <a href="Macro-Pitfalls.html">Macro Pitfalls</a></td><td> </td><td align="left" valign="top">
|
|---|
| 105 | </td></tr>
|
|---|
| 106 | </table>
|
|---|
| 107 |
|
|---|
| 108 | <hr>
|
|---|
| 109 | <div class="header">
|
|---|
| 110 | <p>
|
|---|
| 111 | Next: <a href="Conditionals.html" accesskey="n" rel="next">Conditionals</a>, Previous: <a href="Header-Files.html" accesskey="p" rel="prev">Header Files</a>, Up: <a href="Preprocessing.html" accesskey="u" rel="up">Preprocessing</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Index.html" title="Index" rel="index">Index</a>]</p>
|
|---|
| 112 | </div>
|
|---|
| 113 |
|
|---|
| 114 |
|
|---|
| 115 |
|
|---|
| 116 | </body>
|
|---|
| 117 | </html>
|
|---|
