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87 lines
4.1 KiB
HTML
87 lines
4.1 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Macros - The C Preprocessor</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="The C Preprocessor">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="prev" href="Header-Files.html#Header-Files" title="Header Files">
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<link rel="next" href="Conditionals.html#Conditionals" title="Conditionals">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1987-2015 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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<style type="text/css"><!--
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span.sansserif { font-family:sans-serif; font-weight:normal; }
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Macros"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Conditionals.html#Conditionals">Conditionals</a>,
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Previous: <a rel="previous" accesskey="p" href="Header-Files.html#Header-Files">Header Files</a>,
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Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a>
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<hr>
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</div>
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<h2 class="chapter">3 Macros</h2>
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<p>A <dfn>macro</dfn> 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. <dfn>Object-like</dfn> macros resemble data objects
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when used, <dfn>function-like</dfn> macros resemble function calls.
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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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<ul class="menu">
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<li><a accesskey="1" href="Object_002dlike-Macros.html#Object_002dlike-Macros">Object-like Macros</a>
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<li><a accesskey="2" href="Function_002dlike-Macros.html#Function_002dlike-Macros">Function-like Macros</a>
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<li><a accesskey="3" href="Macro-Arguments.html#Macro-Arguments">Macro Arguments</a>
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<li><a accesskey="4" href="Stringification.html#Stringification">Stringification</a>
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<li><a accesskey="5" href="Concatenation.html#Concatenation">Concatenation</a>
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<li><a accesskey="6" href="Variadic-Macros.html#Variadic-Macros">Variadic Macros</a>
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<li><a accesskey="7" href="Predefined-Macros.html#Predefined-Macros">Predefined Macros</a>
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<li><a accesskey="8" href="Undefining-and-Redefining-Macros.html#Undefining-and-Redefining-Macros">Undefining and Redefining Macros</a>
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<li><a accesskey="9" href="Directives-Within-Macro-Arguments.html#Directives-Within-Macro-Arguments">Directives Within Macro Arguments</a>
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<li><a href="Macro-Pitfalls.html#Macro-Pitfalls">Macro Pitfalls</a>
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</ul>
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</body></html>
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