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87 lines
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87 lines
4.1 KiB
HTML
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<title>Macros - The C Preprocessor</title>
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any later version published by the Free Software Foundation. A copy of
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A GNU Manual
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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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<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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