123 lines
6.4 KiB
HTML
123 lines
6.4 KiB
HTML
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<head>
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<title>The C Preprocessor: Macros</title>
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<link href="Object_002dlike-Macros.html#Object_002dlike-Macros" rel="next" title="Object-like Macros">
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<a name="Macros"></a>
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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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<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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