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57 lines
1.6 KiB
HTML
57 lines
1.6 KiB
HTML
<html>
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<head>
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<title>BOOST_PP_EXPAND</title>
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<link rel="stylesheet" type="text/css" href="../styles.css">
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</head>
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<body>
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<div style="margin-left: 0px;">
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The <b>BOOST_PP_EXPAND</b> macro performs a double macro-expansion on its argument.
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</div>
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<h4>Usage</h4>
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<div class="code">
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<b>BOOST_PP_EXPAND</b>(<i>x</i>)
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</div>
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<h4>Arguments</h4>
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<dl>
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<dt>x</dt>
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<dd>
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The argument to be expanded twice.
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</dd>
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</dl>
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<h4>Remarks</h4>
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<div>
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This macro is useful when a delay is necessary to produce the correct semantics of a macro invocation.
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For example, when a macro expands to an argument list to another macro.
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This macro will expand the the argument list on the first pass, and then rescan to expand any more macros.
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</div>
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<h4>Requirements</h4>
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<div>
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<b>Header:</b> <a href="../headers/facilities/expand.html"><boost/preprocessor/facilities/expand.hpp></a>
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</div>
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<h4>Sample Code</h4>
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<div><pre>
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#include <<a href="../headers/control/if.html">boost/preprocessor/control/if.hpp</a>>
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#include <<a href="../headers/facilities/expand.html">boost/preprocessor/facilities/expand.hpp</a>>
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#define MACRO(a, b, c) (a)(b)(c)
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#define ARGS() (1, 2, 3)
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<a href="expand.html">BOOST_PP_EXPAND</a>(MACRO ARGS()) // expands to (1)(2)(3)
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#define SAMPLE(n) \
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<a href="expand.html">BOOST_PP_EXPAND</a>( \
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MACRO \
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<a href="if.html">BOOST_PP_IF</a>( \
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n, \
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(x, y, z), \
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(a, b, c) \
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) \
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) \
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/**/
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SAMPLE(0) // expands to (a)(b)(c)
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SAMPLE(1) // expands to (x)(y)(z)
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</pre></div>
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</body>
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</html>
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