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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. |
| 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. <dfn>Object-like</dfn> macros resemble data objects |
| when used, <dfn>function-like</dfn> macros resemble function calls. |
| |
| <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++. |
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| <ul class="menu"> |
| <li><a accesskey="1" href="Object_002dlike-Macros.html#Object_002dlike-Macros">Object-like Macros</a> |
| <li><a accesskey="2" href="Function_002dlike-Macros.html#Function_002dlike-Macros">Function-like Macros</a> |
| <li><a accesskey="3" href="Macro-Arguments.html#Macro-Arguments">Macro Arguments</a> |
| <li><a accesskey="4" href="Stringification.html#Stringification">Stringification</a> |
| <li><a accesskey="5" href="Concatenation.html#Concatenation">Concatenation</a> |
| <li><a accesskey="6" href="Variadic-Macros.html#Variadic-Macros">Variadic Macros</a> |
| <li><a accesskey="7" href="Predefined-Macros.html#Predefined-Macros">Predefined Macros</a> |
| <li><a accesskey="8" href="Undefining-and-Redefining-Macros.html#Undefining-and-Redefining-Macros">Undefining and Redefining Macros</a> |
| <li><a accesskey="9" href="Directives-Within-Macro-Arguments.html#Directives-Within-Macro-Arguments">Directives Within Macro Arguments</a> |
| <li><a href="Macro-Pitfalls.html#Macro-Pitfalls">Macro Pitfalls</a> |
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