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- <title>BOOST_PP_EXPAND</title>
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- The <b>BOOST_PP_EXPAND</b> macro performs a double macro-expansion on its argument.
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- <h4>Usage</h4>
- <div class="code">
- <b>BOOST_PP_EXPAND</b>(<i>x</i>)
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- <h4>Arguments</h4>
- <dl>
- <dt>x</dt>
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- The argument to be expanded twice.
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- <h4>Remarks</h4>
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- This macro is useful when a delay is necessary to produce the correct semantics of a macro invocation.
- For example, when a macro expands to an argument list to another macro.
- This macro will expand the argument list on the first pass, and then rescan to expand any more macros.
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- <h4>Requirements</h4>
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- <b>Header:</b> <a href="../headers/facilities/expand.html"><boost/preprocessor/facilities/expand.hpp></a>
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- <h4>Sample Code</h4>
- <div><pre>
- #include <<a href="../headers/control/if.html">boost/preprocessor/control/if.hpp</a>>
- #include <<a href="../headers/facilities/expand.html">boost/preprocessor/facilities/expand.hpp</a>>
- #define MACRO(a, b, c) (a)(b)(c)
- #define ARGS() (1, 2, 3)
- <a href="expand.html">BOOST_PP_EXPAND</a>(MACRO ARGS()) // expands to (1)(2)(3)
- #define SAMPLE(n) \
- <a href="expand.html">BOOST_PP_EXPAND</a>( \
- MACRO \
- <a href="if.html">BOOST_PP_IF</a>( \
- n, \
- (x, y, z), \
- (a, b, c) \
- ) \
- ) \
- /**/
- SAMPLE(0) // expands to (a)(b)(c)
- SAMPLE(1) // expands to (x)(y)(z)
- </pre></div>
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- <div style="margin-left: 0px;">
- <i>© Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i>
- </br><i>© Copyright Paul Mensonides 2002</i>
- </div>
- <div style="margin-left: 0px;">
- <p><small>Distributed under the Boost Software License, Version 1.0. (See
- accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
- copy at <a href=
- "http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
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