1<html> 2 <head> 3 <meta content="text/html; charset=windows-1252" http-equiv="content-type"> 4 <title>BOOST_PP_WHILE_d</title> 5 <link rel="stylesheet" type="text/css" href="../styles.css"> 6 </head> 7 <body> 8 <div style="margin-left: 0px;"> The <b>BOOST_PP_WHILE_<i>d</i></b> macro 9 represents a reentry into the <b>BOOST_PP_WHILE</b> looping construct. </div> 10 <h4>Usage</h4> 11 <div class="code"> <b>BOOST_PP_WHILE_</b> ## <i>d</i>(<i>pred</i>, <i>op</i>, 12 <i>state</i>) </div> 13 <h4>Arguments</h4> 14 <dl> 15 <dt>d</dt> 16 <dd> The next available <b>BOOST_PP_WHILE</b> iteration. </dd> 17 <dt>pred</dt> 18 <dd> A binary predicate of the form <i>pred</i>(<i>d</i>, <i>state</i>). 19 This predicate is expanded by <b>BOOST_PP_WHILE</b> with the next 20 available iteration <i>d</i> and the current <i>state</i>. This 21 predicate must expand to value in the range of <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>. 22 The construct continues to loop until this predicate returns <i>0</i>. 23 When this predicate returns <i>0</i>, <b>BOOST_PP_WHILE</b> returns 24 the current <i>state</i>. </dd> 25 <dt>op</dt> 26 <dd> A binary operation of the form <i>op</i>(<i>d</i>, <i>state</i>). 27 This operation is expanded by <b>BOOST_PP_WHILE</b> with the next 28 available iteration <i>d</i> and the current <i>state</i>. This 29 macro is repeatedly applied to the <i>state</i>, each time producing a 30 new <i>state</i>, until <i>pred</i> returns <i>0</i>. </dd> 31 <dt>state</dt> 32 <dd> The initial state. Often this argument is a <i>tuple</i>. </dd> 33 </dl> 34 <h4>Remarks</h4> 35 <div> This macro iterates <i>op</i>(<i>d</i>, <i>state</i>) while <i>pred</i>(<i>d</i>, 36 <i>state</i>) is non-zero. In other words expands to: 37 <div> <i>op</i>(<i>d</i>, ... <i>op</i>(<i>d</i>, <i>op</i>(<i>d</i>, <i>state</i>)) 38 ... ). </div> 39 </div> 40 <div> At certain times, it may be necessary to perform the concatenation 41 with <b>BOOST_PP_CAT</b> rather than the preprocessor token-pasting 42 operator. This happens when the <i>d</i> value is a macro 43 invocation itself. It needs a delay to allow it to expand. The 44 syntax in such a scenario becomes: 45 <div> <b>BOOST_PP_CAT</b>(<b>BOOST_PP_WHILE_</b>, <i>d</i>)(<i>pred</i>, 46 <i>op</i>, <i>state</i>). </div> 47 </div> 48 <div> Previously, it was possible to concatenate <i>d</i> directly to <b>BOOST_PP_WHILE</b> 49 (without the trailing underscore). This is no longer supported. </div> 50 <h4>See Also</h4> 51 <ul> 52 <li><a href="cat.html">BOOST_PP_CAT</a></li> 53 <li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li> 54 <li><a href="while.html">BOOST_PP_WHILE</a></li> 55 <li><a href="while_d_macros.html"><span style="color: gray;">Macros with D 56 re-entrancy forms</span></a></li> 57 </ul> 58 <h4>Requirements</h4> 59 <div> <b>Header:</b> <a href="../headers/control/while.html"><boost/preprocessor/control/while.hpp></a> 60 </div> 61 <h4>Sample Code</h4> 62 <div> 63 <pre>#include <<a href="../headers/arithmetic/add.html">boost/preprocessor/arithmetic/add.hpp</a>> 64#include <<a href="../headers/arithmetic/dec.html">boost/preprocessor/arithmetic/dec.hpp</a>> 65#include <<a href="../headers/array/elem.html">boost/preprocessor/array/elem.hpp</a>> 66#include <<a href="../headers/array/size.html">boost/preprocessor/array/size.hpp</a>> 67#include <<a href="../headers/control/while.html">boost/preprocessor/control/while.hpp</a>> 68#include <<a href="../headers/tuple/elem.html">boost/preprocessor/tuple/elem.hpp</a>> 69 70#define PRED(d, data) <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 1, data) 71 72#define OP(d, data) \ 73 OP_D( \ 74 d, \ 75 <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 0, data), \ 76 <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 1, data), \ 77 <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 2, data) \ 78 ) \ 79 /**/ 80 81#define OP_D(d, res, i, array) \ 82 ( \ 83 <a href="add_d.html">BOOST_PP_ADD_D</a>( \ 84 d, res, \ 85 <a href="array_elem.html">BOOST_PP_ARRAY_ELEM</a>(<a href="dec.html">BOOST_PP_DEC</a>(i), array)), \ 86 <a href="dec.html">BOOST_PP_DEC</a>(i), \ 87 array \ 88 ) \ 89 /**/ 90 91#define ACCUMULATE_D(d, array) \ 92 <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>( \ 93 3, 0, \ 94 <a href="while_d.html">BOOST_PP_WHILE_</a> ## d( \ 95 PRED, OP, \ 96 (0, <a href="array_size.html">BOOST_PP_ARRAY_SIZE</a>(array), array) \ 97 ) \ 98 ) \ 99 /**/ 100 101#define ARRAY (4, (1, 2, 3, 4)) 102 103ACCUMULATE_D(1, ARRAY)// expands to 10 104</pre></div> 105 <hr size="1"> 106 <div style="margin-left: 0px;"> <i>� Copyright <a href="http://www.housemarque.com" 107 target="_top">Housemarque Oy</a> 2002</i> <br> 108 <i>� Copyright Paul Mensonides 2002<br> 109 </i><i>� Copyright Edward Diener 2014</i><br> 110 </div> 111 <div style="margin-left: 0px;"> 112 <p><small>Distributed under the Boost Software License, Version 1.0. (See 113 accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> 114 or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p> 115 </div> 116 </body> 117</html> 118