1<html> 2<head> 3 <title>BOOST_PP_EXPR_IF</title> 4 <link rel="stylesheet" type="text/css" href="../styles.css"> 5</head> 6<body> 7 <div style="margin-left: 0px;"> 8 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. 9 </div> 10 <h4>Usage</h4> 11 <div class="code"> 12 <b>BOOST_PP_EXPR_IF</b>(<i>cond</i>, <i>expr</i>) 13 </div> 14 <h4>Arguments</h4> 15 <dl> 16 <dt>cond</dt> 17 <dd> 18 The condition that determines if the result is <i>expr</i> or nothing. 19 Valid values range from <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>. 20 </dd> 21 <dt>expr</dt> 22 <dd> 23 The result of the expansion if <i>cond</i> is non-zero. 24 </dd> 25 </dl> 26 <h4>Remarks</h4> 27 <div> 28 This macro performs a boolean conversion on its first argument. 29 If that conversion is unnecessary, use <b>BOOST_PP_EXPR_IIF</b> instead. 30 </div> 31 <h4>See Also</h4> 32 <ul> 33 <li><a href="expr_iif.html">BOOST_PP_EXPR_IIF</a></li> 34 <li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li> 35 </ul> 36 <h4>Requirements</h4> 37 <div> 38 <b>Header:</b> <a href="../headers/control/expr_if.html"><boost/preprocessor/control/expr_if.hpp></a> 39 </div> 40 <h4>Sample Code</h4> 41<div><pre> 42#include <<a href="../headers/control/expr_if.html">boost/preprocessor/control/expr_if.hpp</a>> 43#include <<a href="../headers/tuple/elem.html">boost/preprocessor/tuple/elem.hpp</a>> 44 45#define CV(n) \ 46 <a href="expr_if.html">BOOST_PP_EXPR_IF</a>( \ 47 n, \ 48 <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>( \ 49 4, n, \ 50 (..., const, volatile, const volatile) \ 51 ) \ 52 ) \ 53 /**/ 54 55CV(0) // expands to nothing 56CV(1) // expands to const 57</pre></div> 58 <hr size="1"> 59 <div style="margin-left: 0px;"> 60 <i>� Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i> 61 </br><i>� Copyright Paul Mensonides 2002</i> 62 </div> 63 <div style="margin-left: 0px;"> 64 <p><small>Distributed under the Boost Software License, Version 1.0. (See 65 accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or 66 copy at <a href= 67 "http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p> 68 </div> 69</body> 70</html> 71