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| <title>BOOST_PP_WHILE_d</title> |
| <link rel="stylesheet" type="text/css" href="../styles.css"> |
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| <body> |
| <div style="margin-left: 0px;"> |
| The <b>BOOST_PP_WHILE_<i>d</i></b> macro represents a reentry into the <b>BOOST_PP_WHILE</b> looping construct. |
| </div> |
| <h4>Usage</h4> |
| <div class="code"> |
| <b>BOOST_PP_WHILE_</b> ## <i>d</i>(<i>pred</i>, <i>op</i>, <i>state</i>) |
| </div> |
| <h4>Arguments</h4> |
| <dl> |
| <dt>d</dt> |
| <dd> |
| The next available <b>BOOST_PP_WHILE</b> iteration. |
| </dd> |
| <dt>pred</dt> |
| <dd> |
| A binary predicate of the form <i>pred</i>(<i>d</i>, <i>state</i>). |
| This predicate is expanded by <b>BOOST_PP_WHILE</b> with the next available |
| iteration <i>d</i> and the current <i>state</i>. |
| This predicate must expand to value in the range of <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>. |
| The construct continues to loop until this predicate returns <i>0</i>. |
| When this predicate returns <i>0</i>, <b>BOOST_PP_WHILE</b> returns the current <i>state</i>. |
| </dd> |
| <dt>op</dt> |
| <dd> |
| A binary operation of the form <i>op</i>(<i>d</i>, <i>state</i>). |
| This operation is expanded by <b>BOOST_PP_WHILE</b> with the next available |
| iteration <i>d</i> and the current <i>state</i>. |
| This macro is repeatedly applied to the <i>state</i>, each time producing a new <i>state</i>, until <i>pred</i> returns <i>0</i>. |
| </dd> |
| <dt>state</dt> |
| <dd> |
| The initial state. |
| Often this argument is a <i>tuple</i>. |
| </dd> |
| </dl> |
| <h4>Remarks</h4> |
| <div> |
| This macro iterates <i>op</i>(<i>d</i>, <i>state</i>) while <i>pred</i>(<i>d</i>, <i>state</i>) is non-zero. |
| In other words expands to: |
| <div> |
| <i>op</i>(<i>d</i>, ... <i>op</i>(<i>d</i>, <i>op</i>(<i>d</i>, <i>state</i>)) ... ). |
| </div> |
| </div> |
| <div> |
| At certain times, it may be necessary to perform the concatenation with <b>BOOST_PP_CAT</b> rather than the preprocessor token-pasting operator. |
| This happens when the <i>d</i> value is a macro invocation itself. |
| It needs a delay to allow it to expand. |
| The syntax in such a scenario becomes: |
| <div> |
| <b>BOOST_PP_CAT</b>(<b>BOOST_PP_WHILE_</b>, <i>d</i>)(<i>pred</i>, <i>op</i>, <i>state</i>). |
| </div> |
| </div> |
| <div> |
| Previously, it was possible to concatenate <i>d</i> directly to <b>BOOST_PP_WHILE</b> (without the trailing underscore). |
| This is no longer supported. |
| </div> |
| <h4>See Also</h4> |
| <ul> |
| <li><a href="cat.html">BOOST_PP_CAT</a></li> |
| <li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li> |
| <li><a href="while.html">BOOST_PP_WHILE</a></li> |
| </ul> |
| <h4>Requirements</h4> |
| <div> |
| <b>Header:</b> <a href="../headers/control/while.html"><boost/preprocessor/control/while.hpp></a> |
| </div> |
| <h4>Sample Code</h4> |
| <div><pre> |
| #include <<a href="../headers/arithmetic/add.html">boost/preprocessor/arithmetic/add.hpp</a>> |
| #include <<a href="../headers/arithmetic/dec.html">boost/preprocessor/arithmetic/dec.hpp</a>> |
| #include <<a href="../headers/array/elem.html">boost/preprocessor/array/elem.hpp</a>> |
| #include <<a href="../headers/array/size.html">boost/preprocessor/array/size.hpp</a>> |
| #include <<a href="../headers/control/while.html">boost/preprocessor/control/while.hpp</a>> |
| #include <<a href="../headers/tuple/elem.html">boost/preprocessor/tuple/elem.hpp</a>> |
| |
| #define PRED(d, data) <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 1, data) |
| |
| #define OP(d, data) \ |
| OP_D( \ |
| d, \ |
| <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 0, data), \ |
| <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 1, data), \ |
| <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 2, data) \ |
| ) \ |
| /**/ |
| |
| #define OP_D(d, res, i, array) \ |
| ( \ |
| <a href="add_d.html">BOOST_PP_ADD_D</a>( \ |
| d, res, \ |
| <a href="array_elem.html">BOOST_PP_ARRAY_ELEM</a>(<a href="dec.html">BOOST_PP_DEC</a>(i), array)), \ |
| <a href="dec.html">BOOST_PP_DEC</a>(i), \ |
| array \ |
| ) \ |
| /**/ |
| |
| #define ACCUMULATE_D(d, array) \ |
| <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>( \ |
| 3, 0, \ |
| <a href="while_d.html">BOOST_PP_WHILE_</a> ## d( \ |
| PRED, OP, \ |
| (0, <a href="array_size.html">BOOST_PP_ARRAY_SIZE</a>(array), array) \ |
| ) \ |
| ) \ |
| /**/ |
| |
| #define ARRAY (4, (1, 2, 3, 4)) |
| |
| ACCUMULATE_D(1, ARRAY)// expands to 10 |
| </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> |
| </div> |
| </body> |
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