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| <title>The C Preprocessor: Macros</title> |
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| <a name="Macros-1"></a> |
| <h2 class="chapter">3 Macros</h2> |
| |
| <p>A <em>macro</em> is a fragment of code which has been given a name. |
| Whenever the name is used, it is replaced by the contents of the macro. |
| There are two kinds of macros. They differ mostly in what they look |
| like when they are used. <em>Object-like</em> macros resemble data objects |
| when used, <em>function-like</em> macros resemble function calls. |
| </p> |
| <p>You may define any valid identifier as a macro, even if it is a C |
| keyword. The preprocessor does not know anything about keywords. This |
| can be useful if you wish to hide a keyword such as <code>const</code> from an |
| older compiler that does not understand it. However, the preprocessor |
| operator <code>defined</code> (see <a href="Defined.html#Defined">Defined</a>) can never be defined as a |
| 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 |
| macros when you are compiling C++. |
| </p> |
| <table class="menu" border="0" cellspacing="0"> |
| <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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| <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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| <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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| <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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| <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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| <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"> |
| </td></tr> |
| <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"> |
| </td></tr> |
| <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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| <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"> |
| </td></tr> |
| <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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