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[SVN r15693]
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Paul Mensonides
2002-10-03 22:13:37 +00:00
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<html>
<head>
<title>BOOST_PP_EXPAND</title>
<link rel="stylesheet" type="text/css" href="../styles.css">
</head>
<body>
<div style="margin-left: 0px;">
The <b>BOOST_PP_EXPAND</b> macro performs a double macro-expansion on its argument.
</div>
<h4>Usage</h4>
<div class="code">
<b>BOOST_PP_EXPAND</b>(<i>x</i>)
</div>
<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.&nbsp;
For example, when a macro expands to an argument list to another macro.&nbsp;
This macro will expand the the argument list on the first pass, and then rescan to expand any more macros.
</div>
<h4>Requirements</h4>
<div>
<b>Header:</b> &nbsp;<a href="../headers/facilities/expand.hpp.html">&lt;boost/preprocessor/facilities/expand.hpp&gt;</a>
</div>
<h4>Sample Code</h4>
<div><pre>
#include &lt;<a href="../headers/control/if.hpp.html">boost/preprocessor/control/if.hpp</a>&gt;
#include &lt;<a href="../headers/facilities/expand.hpp.html">boost/preprocessor/facilities/expand.hpp</a>&gt;
#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>
</body>
</html>