106 lines
4.7 KiB
HTML
106 lines
4.7 KiB
HTML
<html>
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<head>
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<title>BOOST_PP_FOR</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;">
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The <b>BOOST_PP_FOR</b> macro represents a generalized horizontal repetition construct.
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</div>
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<h4>Usage</h4>
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<div class="code">
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<b>BOOST_PP_FOR</b>(<i>state</i>, <i>pred</i>, <i>op</i>, <i>macro</i>)
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</div>
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<h4>Arguments</h4>
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<dl>
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<dt>state</dt>
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<dd>
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The initial state.
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</dd>
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<dt>pred</dt>
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<dd>
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A binary predicate of the form <i>pred</i>(<i>r</i>, <i>state</i>).
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This macro must expand to an integer in the range of <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>.
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<b>BOOST_PP_FOR</b> repeatedly expands <i>macro</i> while this predicate returns non-zero.
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This macro is called with the next available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.
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</dd>
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<dt>op</dt>
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<dd>
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A binary operation of the form <i>op</i>(<i>r</i>, <i>state</i>).
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This operation is expanded by <b>BOOST_PP_FOR</b> with the next available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.
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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>.
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</dd>
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<dt>macro</dt>
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<dd>
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A binary macro of the form <i>macro</i>(<i>r</i>, <i>state</i>).
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This macro is expanded by <b>BOOST_PP_FOR</b> with the next available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.
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This macro is is repeated by <b>BOOST_PP_FOR</b> until <i>pred</i> returns <i>0</i>.
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</dd>
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</dl>
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<h4>Remarks</h4>
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<div>
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This macro expands to the sequence:
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<div>
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<i>macro</i>(<i>r</i>, <i>state</i>) <i>macro</i>(<i>r</i>, <i>op</i>(<i>r</i>, <i>state</i>)) ... <i>macro</i>(<i>r</i>, <i>op</i>(<i>r</i>, ... <i>op</i>(<i>r</i>, <i>state</i>) ... ))
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</div>
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</div>
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<div>
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The <i>r</i> value that is passed to <i>pred</i>, <i>op</i>, and <i>macro</i> represents the next available <b>BOOST_PP_FOR</b> repetition.
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Other macros that have <b>_R</b> suffix variants internally use <b>BOOST_PP_FOR</b>--for example, <b>BOOST_PP_LIST_FOR_EACH</b> and <b>BOOST_PP_LIST_FOR_EACH_R</b>.
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Using these <b>_R</b> versions is not strictly necessary, but passing the <i>r</i> value (that is passed to <i>pred</i>, <i>op</i>, and <i>macro</i>) to these macros allows them to reenter <b>BOOST_PP_FOR</b> with maximum efficiency.
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</div>
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<div>
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To directly use this <i>r</i> value, rather than simply passing it to another macro, see <b>BOOST_PP_FOR_<i>r</i></b>.
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</div>
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<div>
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Previously, this macro could not be used recursively inside <b>BOOST_PP_FOR</b>.
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This limitation no longer exists, as the library can automatically detect the next available <b>BOOST_PP_FOR</b> repetition.
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</div>
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<h4>See Also</h4>
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<ul>
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<li><a href="for_r.html">BOOST_PP_FOR_<i>r</i></a></li>
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<li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li>
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</ul>
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<h4>Requirements</h4>
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<div>
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<b>Header:</b> <a href="../headers/repetition/for.html"><boost/preprocessor/repetition/for.hpp></a>
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</div>
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<h4>Sample Code</h4>
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<div><pre>
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#include <<a href="../headers/arithmetic/inc.html">boost/preprocessor/arithmetic/inc.hpp</a>>
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#include <<a href="../headers/comparison/not_equal.html">boost/preprocessor/comparison/not_equal.hpp</a>>
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#include <<a href="../headers/repetition/for.html">boost/preprocessor/repetition/for.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(r, state) \
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<a href="not_equal.html">BOOST_PP_NOT_EQUAL</a>( \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(2, 0, state), \
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<a href="inc.html">BOOST_PP_INC</a>(<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(2, 1, state)) \
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) \
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/**/
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#define OP(r, state) \
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( \
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<a href="inc.html">BOOST_PP_INC</a>(<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(2, 0, state)), \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(2, 1, state) \
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) \
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/**/
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#define MACRO(r, state) <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(2, 0, state)
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<a href="for.html">BOOST_PP_FOR</a>((5, 10), PRED, OP, MACRO) // expands to 5 6 7 8 9 10
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</pre></div>
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<hr size="1">
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<div style="margin-left: 0px;">
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<i><EFBFBD> Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i>
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</br><i><EFBFBD> Copyright Paul Mensonides 2002</i>
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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> or
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copy at <a href=
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"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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