| Brian Silverman | f27e085 | 2018-08-04 23:56:45 -0700 | [diff] [blame^] | 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 | |
| 103 | ACCUMULATE_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> |