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<title>BOOST_PP_EXPAND</title>
<link rel="stylesheet" type="text/css" href="../styles.css">
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<body>
<div style="margin-left: 0px;">
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>
<dd>
The argument to be expanded twice.
</dd>
</dl>
<h4>Remarks</h4>
<div>
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 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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