projects / ceph.git / blame
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|---|---|---|
| 7c673cae FG |
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 | ||
| 55 | CV(0) // expands to nothing | |
| 56 | CV(1) // expands to const | |
| 57 | </pre></div> | |
| 58 | <hr size="1"> | |
| 59 | <div style="margin-left: 0px;"> | |
| 60 |