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| <title>BOOST_PP_EXPR_IF</title> |
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| The <b>BOOST_PP_EXPR_IF</b> macro expands to its second argument if its first argument is non-zero or expands to nothing otherwise. |
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| <h4>Usage</h4> |
| <div class="code"> |
| <b>BOOST_PP_EXPR_IF</b>(<i>cond</i>, <i>expr</i>) |
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| <h4>Arguments</h4> |
| <dl> |
| <dt>cond</dt> |
| <dd> |
| The condition that determines if the result is <i>expr</i> or nothing. |
| Valid values range from <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>. |
| </dd> |
| <dt>expr</dt> |
| <dd> |
| The result of the expansion if <i>cond</i> is non-zero. |
| </dd> |
| </dl> |
| <h4>Remarks</h4> |
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| This macro performs a boolean conversion on its first argument. |
| If that conversion is unnecessary, use <b>BOOST_PP_EXPR_IIF</b> instead. |
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| <h4>See Also</h4> |
| <ul> |
| <li><a href="expr_iif.html">BOOST_PP_EXPR_IIF</a></li> |
| <li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li> |
| </ul> |
| <h4>Requirements</h4> |
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| <b>Header:</b> <a href="../headers/control/expr_if.html"><boost/preprocessor/control/expr_if.hpp></a> |
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| <h4>Sample Code</h4> |
| <div><pre> |
| #include <<a href="../headers/control/expr_if.html">boost/preprocessor/control/expr_if.hpp</a>> |
| #include <<a href="../headers/tuple/elem.html">boost/preprocessor/tuple/elem.hpp</a>> |
| |
| #define CV(n) \ |
| <a href="expr_if.html">BOOST_PP_EXPR_IF</a>( \ |
| n, \ |
| <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>( \ |
| 4, n, \ |
| (..., const, volatile, const volatile) \ |
| ) \ |
| ) \ |
| /**/ |
| |
| CV(0) // expands to nothing |
| CV(1) // expands to const |
| </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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