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| <title>BOOST_PP_LIST_FILTER</title> |
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| The <b>BOOST_PP_LIST_FILTER</b> macro filters a <i>list</i> according to a supplied criterion. |
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| <h4>Usage</h4> |
| <div class="code"> |
| <b>BOOST_PP_LIST_FILTER</b>(<i>pred</i>, <i>data</i>, <i>list</i>) |
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| <h4>Arguments</h4> |
| <dl> |
| <dt>pred</dt> |
| <dd> |
| A ternary predicate of the form <i>pred</i>(<i>d</i>, <i>data</i>, <i>elem</i>). |
| This predicate is expanded by <b>BOOST_PP_LIST_FILTER</b> for each element in <i>list</i> with the next available <b>BOOST_PP_WHILE</b> iteration, |
| the auxiliary <i>data</i>, and the current element in <i>list</i>. |
| This macro must return a integral value in the range of <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>. |
| If this predicate expands to non-zero for a certain element, that element is included in the resulting <i>list</i>. |
| </dd> |
| <dt>data</dt> |
| <dd> |
| Auxiliary data passed to <i>pred</i>. |
| </dd> |
| <dt>list</dt> |
| <dd> |
| The <i>list</i> to be filtered. |
| </dd> |
| </dl> |
| <h4>Remarks</h4> |
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| This macro expands <i>pred</i> for each element in <i>list</i>. |
| It builds a new <i>list</i> out of each element for which <i>pred</i> returns non-zero. |
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| Previously, this macro could not be used inside <b>BOOST_PP_WHILE</b>. |
| There is no longer any such restriction. |
| It is more efficient, however, to use <b>BOOST_PP_LIST_FILTER_D</b> in such a situation. |
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| <h4>See Also</h4> |
| <ul> |
| <li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li> |
| <li><a href="list_filter_d.html">BOOST_PP_LIST_FILTER_D</a></li> |
| </ul> |
| <h4>Requirements</h4> |
| <div> |
| <b>Header:</b> <a href="../headers/list/filter.html"><boost/preprocessor/list/filter.hpp></a> |
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| <h4>Sample Code</h4> |
| <div><pre> |
| #include <<a href="../headers/comparison/less_equal.html">boost/preprocessor/comparison/less_equal.hpp</a>> |
| #include <<a href="../headers/list/filter.html">boost/preprocessor/list/filter.hpp</a>> |
| |
| #define LIST (1, (3, (2, (5, <a href="nil.html">BOOST_PP_NIL</a>)))) |
| |
| #define PRED(d, data, elem) <a href="less_equal.html">BOOST_PP_LESS_EQUAL</a>(elem, data) |
| |
| <a href="list_filter.html">BOOST_PP_LIST_FILTER</a>(PRED, 3, LIST) |
| // expands to (1, (3, (2, <a href="nil.html">BOOST_PP_NIL</a>))) |
| </pre></div> |
| <hr size="1"> |
| <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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