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2002-02-05 12:13:37 +00:00
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<title>Boost.Preprocessor - Reference</title>
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2002-02-04 14:57:59 +00:00
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<td valign="top" width="300">
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<h3><a href="../../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
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<td valign="top">
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<h1 align="center">Boost.Preprocessor</h1>
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<h2 align="center">Reference</h2>
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</table>
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2002-01-31 15:36:01 +00:00
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2002-02-04 14:57:59 +00:00
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<hr>
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2002-01-31 15:36:01 +00:00
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2002-03-11 16:11:34 +00:00
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<a href="expr_if.htm">Prev</a> <a href="identity.htm">Next</a> <a href="index.htm#Macros">Macros</a> <a href="index.htm#Headers">Headers</a>
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<hr>
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2002-02-04 14:57:59 +00:00
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<h1>#include <<a href="../../../../boost/preprocessor/for.hpp">boost/preprocessor/for.hpp</a>></h1>
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<hr>
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2002-02-04 14:57:59 +00:00
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<h2><a name="BOOST_PP_FOR">#define BOOST_PP_FOR</a>(X,C,F,I)</h2>
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<p>Repeats <code>I(R,X)</code> and iterates <code>F(R,X)</code> while
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<code>C(R,X)</code> is true.</p>
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<p>In other words, expands to the sequence:</p>
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<pre>
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I(R,X) I(R,F(R,X)) I(R,F(R,F(R,X))) ... I(R,F(R,F(...F(R,X)...)))
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</pre>
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<p>The length of the sequence is determined by <code>C(R,X)</code>.</p>
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2002-03-10 12:31:37 +00:00
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<p>For example,</p>
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<pre>
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#define C(R,X) <a href="comparison_less.htm#BOOST_PP_LESS">BOOST_PP_LESS</a>(<a href="tuple_elem.htm#BOOST_PP_TUPLE_ELEM">BOOST_PP_TUPLE_ELEM</a>(2,0,X),<a href="tuple_elem.htm#BOOST_PP_TUPLE_ELEM">BOOST_PP_TUPLE_ELEM</a>(2,1,X))
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#define F(R,X) (<a href="inc.htm#BOOST_PP_INC">BOOST_PP_INC</a>(<a href="tuple_elem.htm#BOOST_PP_TUPLE_ELEM">BOOST_PP_TUPLE_ELEM</a>(2,0,X)),<a href="tuple_elem.htm#BOOST_PP_TUPLE_ELEM">BOOST_PP_TUPLE_ELEM</a>(2,1,X))
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#define I(R,X) <a href="tuple_elem.htm#BOOST_PP_TUPLE_ELEM">BOOST_PP_TUPLE_ELEM</a>(2,0,X)
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<a href="for.htm#BOOST_PP_FOR">BOOST_PP_FOR</a>((0,3),C,F,I)
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</pre>
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<p>expands to:</p>
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<pre>
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0 1 2
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</pre>
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<h3>Legend</h3>
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<ul>
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<li><b>X</b> is the current state of iteration. The state is usually a tuple.</li>
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<li><b>C</b> is the condition for iteration. It must expand to a decimal
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integer literal.</li>
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<li><b>F</b> is the iterated macro. Note that if the state is a tuple, then
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F(R,X) usually expands to a tuple of the same number of elements.</li>
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<li><b>I</b> is the state instantiation macro.</li>
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<li><b>R</b> is the recursion depth and should only be used as a parameter to
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other macros using <a href="for.htm#BOOST_PP_FOR">BOOST_PP_FOR</a>() or for invoking <a href="for.htm#BOOST_PP_FOR">BOOST_PP_FOR</a>##R()
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directly. For each macro using <a href="for.htm#BOOST_PP_FOR">BOOST_PP_FOR</a>(), there is a version of the
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macro, distinguished by the R suffix, that accepts an additional
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recursion depth as the first parameter. This technique is necessary to
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avoid recursively expanding the same macro again, which is not permitted
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by the C++ preprocessor.</li>
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</ul>
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<h3><a href="repeat.htm#BOOST_PP_REPEAT">BOOST_PP_REPEAT</a>() vs <a href="for.htm#BOOST_PP_FOR">BOOST_PP_FOR</a>()</h3>
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<p><a href="for.htm#BOOST_PP_FOR">BOOST_PP_FOR</a>() is a generalization of <a href="repeat.htm#BOOST_PP_REPEAT">BOOST_PP_REPEAT</a>(). This means that
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<a href="repeat.htm#BOOST_PP_REPEAT">BOOST_PP_REPEAT</a>() can be implemented using <a href="for.htm#BOOST_PP_FOR">BOOST_PP_FOR</a>(). However,
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<a href="repeat.htm#BOOST_PP_REPEAT">BOOST_PP_REPEAT</a>() was introduced earlier, is generally easier to use, and is
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still quite useful on its own.</p>
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<h3>2D and 3D repetition</h3>
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<p><a href="for.htm#BOOST_PP_FOR">BOOST_PP_FOR</a>() can be used for multidimensional repetition simply by
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invoking <a href="for.htm#BOOST_PP_FOR">BOOST_PP_FOR</a>##R() directly.</p>
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2002-02-05 12:16:25 +00:00
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<h3>Test</h3>
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<ul>
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<li><a href="../../test/for_test.cpp">for_test.cpp</a></li>
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</ul>
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2002-02-04 14:57:59 +00:00
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<hr>
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2002-01-31 15:36:01 +00:00
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2002-03-11 16:11:34 +00:00
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<a href="expr_if.htm">Prev</a> <a href="identity.htm">Next</a> <a href="index.htm#Macros">Macros</a> <a href="index.htm#Headers">Headers</a>
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2002-01-31 15:36:01 +00:00
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<hr>
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2002-02-04 14:57:59 +00:00
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<p>Revised <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %b %Y" startspan --><!--webbot bot="Timestamp" endspan i-checksum="15246" --></p>
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2002-02-04 14:57:59 +00:00
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<p><i>© Copyright <a href="http://www.housemarque.com">Housemarque Oy</a> 2002</i></p>
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<p><i>Permission to copy, use, modify, sell and distribute this document is granted
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provided this copyright notice appears in all copies. This document is provided
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"as is" without express or implied warranty, and with no claim as to its suitability
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for any purpose.</i></p>
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</body></html>
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