118 lines
5.3 KiB
HTML
118 lines
5.3 KiB
HTML
<html>
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<head>
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<meta content="text/html; charset=windows-1252" http-equiv="content-type">
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<title>BOOST_PP_WHILE_d</title>
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<link rel="stylesheet" type="text/css" href="../styles.css">
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</head>
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<body>
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<div style="margin-left: 0px;"> The <b>BOOST_PP_WHILE_<i>d</i></b> macro
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represents a reentry into the <b>BOOST_PP_WHILE</b> looping construct. </div>
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<h4>Usage</h4>
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<div class="code"> <b>BOOST_PP_WHILE_</b> ## <i>d</i>(<i>pred</i>, <i>op</i>,
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<i>state</i>) </div>
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<h4>Arguments</h4>
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<dl>
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<dt>d</dt>
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<dd> The next available <b>BOOST_PP_WHILE</b> iteration. </dd>
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<dt>pred</dt>
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<dd> A binary predicate of the form <i>pred</i>(<i>d</i>, <i>state</i>).
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This predicate is expanded by <b>BOOST_PP_WHILE</b> with the next
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available iteration <i>d</i> and the current <i>state</i>. This
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predicate must expand to value in the range of <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>.
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The construct continues to loop until this predicate returns <i>0</i>.
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When this predicate returns <i>0</i>, <b>BOOST_PP_WHILE</b> returns
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the current <i>state</i>. </dd>
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<dt>op</dt>
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<dd> A binary operation of the form <i>op</i>(<i>d</i>, <i>state</i>).
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This operation is expanded by <b>BOOST_PP_WHILE</b> with the next
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available iteration <i>d</i> and the current <i>state</i>. This
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macro is repeatedly applied to the <i>state</i>, each time producing a
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new <i>state</i>, until <i>pred</i> returns <i>0</i>. </dd>
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<dt>state</dt>
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<dd> The initial state. Often this argument is a <i>tuple</i>. </dd>
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</dl>
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<h4>Remarks</h4>
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<div> This macro iterates <i>op</i>(<i>d</i>, <i>state</i>) while <i>pred</i>(<i>d</i>,
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<i>state</i>) is non-zero. In other words expands to:
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<div> <i>op</i>(<i>d</i>, ... <i>op</i>(<i>d</i>, <i>op</i>(<i>d</i>, <i>state</i>))
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... ). </div>
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</div>
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<div> At certain times, it may be necessary to perform the concatenation
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with <b>BOOST_PP_CAT</b> rather than the preprocessor token-pasting
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operator. This happens when the <i>d</i> value is a macro
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invocation itself. It needs a delay to allow it to expand. The
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syntax in such a scenario becomes:
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<div> <b>BOOST_PP_CAT</b>(<b>BOOST_PP_WHILE_</b>, <i>d</i>)(<i>pred</i>,
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<i>op</i>, <i>state</i>). </div>
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</div>
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<div> Previously, it was possible to concatenate <i>d</i> directly to <b>BOOST_PP_WHILE</b>
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(without the trailing underscore). This is no longer supported. </div>
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<h4>See Also</h4>
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<ul>
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<li><a href="cat.html">BOOST_PP_CAT</a></li>
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<li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li>
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<li><a href="while.html">BOOST_PP_WHILE</a></li>
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<li><a href="while_d_macros.html"><span style="color: gray;">Macros with D
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re-entrancy forms</span></a></li>
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</ul>
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<h4>Requirements</h4>
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<div> <b>Header:</b> <a href="../headers/control/while.html"><boost/preprocessor/control/while.hpp></a>
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</div>
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<h4>Sample Code</h4>
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<div>
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<pre>#include <<a href="../headers/arithmetic/add.html">boost/preprocessor/arithmetic/add.hpp</a>>
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#include <<a href="../headers/arithmetic/dec.html">boost/preprocessor/arithmetic/dec.hpp</a>>
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#include <<a href="../headers/array/elem.html">boost/preprocessor/array/elem.hpp</a>>
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#include <<a href="../headers/array/size.html">boost/preprocessor/array/size.hpp</a>>
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#include <<a href="../headers/control/while.html">boost/preprocessor/control/while.hpp</a>>
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#include <<a href="../headers/tuple/elem.html">boost/preprocessor/tuple/elem.hpp</a>>
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#define PRED(d, data) <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 1, data)
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#define OP(d, data) \
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OP_D( \
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d, \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 0, data), \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 1, data), \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 2, data) \
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) \
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/**/
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#define OP_D(d, res, i, array) \
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( \
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<a href="add_d.html">BOOST_PP_ADD_D</a>( \
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d, res, \
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<a href="array_elem.html">BOOST_PP_ARRAY_ELEM</a>(<a href="dec.html">BOOST_PP_DEC</a>(i), array)), \
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<a href="dec.html">BOOST_PP_DEC</a>(i), \
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array \
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) \
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/**/
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#define ACCUMULATE_D(d, array) \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>( \
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3, 0, \
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<a href="while_d.html">BOOST_PP_WHILE_</a> ## d( \
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PRED, OP, \
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(0, <a href="array_size.html">BOOST_PP_ARRAY_SIZE</a>(array), array) \
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) \
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) \
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/**/
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#define ARRAY (4, (1, 2, 3, 4))
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ACCUMULATE_D(1, ARRAY)// expands to 10
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</pre></div>
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<hr size="1">
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<div style="margin-left: 0px;"> <i><EFBFBD> Copyright <a href="http://www.housemarque.com"
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target="_top">Housemarque Oy</a> 2002</i> <br>
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<i><EFBFBD> Copyright Paul Mensonides 2002<br>
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</i><i><EFBFBD> Copyright Edward Diener 2014</i><br>
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</div>
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<div style="margin-left: 0px;">
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<p><small>Distributed under the Boost Software License, Version 1.0. (See
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accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a>
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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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</div>
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</body>
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</html>
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