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| 1 | <html> |
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| 2 | <head> |
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| 3 | <title>BOOST_PP_EXPAND</title> |
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| 4 | <link rel="stylesheet" type="text/css" href="../styles.css"> |
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| 5 | </head> |
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| 6 | <body> |
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| 7 | <div style="margin-left: 0px;"> |
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| 8 | The <b>BOOST_PP_EXPAND</b> macro performs a double macro-expansion on its argument. |
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| 9 | </div> |
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| 10 | <h4>Usage</h4> |
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| 11 | <div class="code"> |
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| 12 | <b>BOOST_PP_EXPAND</b>(<i>x</i>) |
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| 13 | </div> |
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| 14 | <h4>Arguments</h4> |
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| 15 | <dl> |
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| 16 | <dt>x</dt> |
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| 17 | <dd> |
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| 18 | The argument to be expanded twice. |
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| 19 | </dd> |
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| 20 | </dl> |
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| 21 | <h4>Remarks</h4> |
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| 22 | <div> |
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| 23 | This macro is useful when a delay is necessary to produce the correct semantics of a macro invocation. |
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| 24 | For example, when a macro expands to an argument list to another macro. |
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| 25 | This macro will expand the the argument list on the first pass, and then rescan to expand any more macros. |
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| 26 | </div> |
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| 27 | <h4>Requirements</h4> |
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| 28 | <div> |
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| 29 | <b>Header:</b> <a href="../headers/facilities/expand.html"><boost/preprocessor/facilities/expand.hpp></a> |
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| 30 | </div> |
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| 31 | <h4>Sample Code</h4> |
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| 32 | <div><pre> |
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| 33 | #include <<a href="../headers/control/if.html">boost/preprocessor/control/if.hpp</a>> |
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| 34 | #include <<a href="../headers/facilities/expand.html">boost/preprocessor/facilities/expand.hpp</a>> |
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| 35 | |
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| 36 | #define MACRO(a, b, c) (a)(b)(c) |
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| 37 | #define ARGS() (1, 2, 3) |
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| 38 | |
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| 39 | <a href="expand.html">BOOST_PP_EXPAND</a>(MACRO ARGS()) // expands to (1)(2)(3) |
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| 40 | |
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| 41 | #define SAMPLE(n) \ |
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| 42 | <a href="expand.html">BOOST_PP_EXPAND</a>( \ |
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| 43 | MACRO \ |
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| 44 | <a href="if.html">BOOST_PP_IF</a>( \ |
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| 45 | n, \ |
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| 46 | (x, y, z), \ |
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| 47 | (a, b, c) \ |
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| 48 | ) \ |
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| 49 | ) \ |
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| 50 | /**/ |
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| 51 | |
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| 52 | SAMPLE(0) // expands to (a)(b)(c) |
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| 53 | SAMPLE(1) // expands to (x)(y)(z) |
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| 54 | </pre></div> |
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| 55 | </body> |
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| 56 | </html> |
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