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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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