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<HTML><HEAD><TITLE>Boost PREPROCESSOR library</TITLE><BODY bgcolor="#FFFFFF">
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<title>Boost.Preprocessor</title>
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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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<h1 align="center">Boost.Preprocessor</h1>
<h2 align="center">Reference</h2>
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<H1>#include &lt;<a href="../../../../boost/preprocessor/while.hpp">boost/preprocessor/while.hpp</a>&gt;</H1>
<a href="tuple_to_list.htm">Prev</a> <a href="arithmetic.htm">Next</a> <a href="index.htm#Macros">Macros</a> <a href="index.htm#Headers">Headers</a>
<hr>
<h1>#include &lt;<a href="../../../../boost/preprocessor/while.hpp">boost/preprocessor/while.hpp</a>&gt;</h1>
<hr>
<H2><a name="BOOST_PP_WHILE">#define BOOST_PP_WHILE</a>(C,F,X)</H2>
<P>Iterates F(D,X) while C(D,X) is true.</P>
<h2><a name="BOOST_PP_WHILE">#define BOOST_PP_WHILE</a>(C,F,X)</h2>
<p>Iterates <code>F(D,X)</code> while <code>C(D,X)</code> is true.</p>
<P>In other words, expands to:</P>
<p>In other words, expands to:</p>
<PRE>
<pre>
F(D, ... F(D, F(D,X) ) ... )
</PRE>
</pre>
<P>The depth of iteration is determined by C(D,X).</P>
<p>The depth of iteration is determined by <code>C(D,X)</code>.</p>
<H3>Legend</H3>
<UL>
<LI><B>X</B> is the current state of iteration. The state is usually a tuple.
<LI><B>C</B> is the condition for iteration. It must expand to a decimal
integer literal.
<LI><B>F</B> is the iterated macro. Note that if the state is a tuple, then
F(D,X) usually expands to a tuple of the same number of elements.
<LI><B>D</B> is the recursion depth and should only be used as a parameter
<h3>Legend</h3>
<ul>
<li><b>X</b> is the current state of iteration. The state is usually a tuple.</li>
<li><b>C</b> is the condition for iteration. It must expand to a decimal
integer literal.</li>
<li><b>F</b> is the iterated macro. Note that if the state is a tuple, then
F(D,X) usually expands to a tuple of the same number of elements.</li>
<li><b>D</b> is the recursion depth and should only be used as a parameter
to other macros using <a href="while.htm#BOOST_PP_WHILE">BOOST_PP_WHILE</a>(). Such macros include
<a href="arithmetic_add.htm#BOOST_PP_ADD">BOOST_PP_ADD</a>() and other arithmetic operations. For each macro using
<a href="while.htm#BOOST_PP_WHILE">BOOST_PP_WHILE</a>(), there is a version of the macro, distinguished by the
D suffix (e.g. BOOST_PP_ADD_D()), that accepts an additional recursion
depth as the first parameter. This technique is necessary to avoid
recursively expanding the same macro again, which is not permitted by the
C++ preprocessor. Note that the value of the D parameter may exceed
<a href="limits.htm#BOOST_PP_LIMIT_MAG">BOOST_PP_LIMIT_MAG</a>.
</UL>
C++ preprocessor.</li>
</ul>
<H3>Note</H3>
<h3>Note</h3>
<ul>
<li>The value of the D parameter may exceed <a href="limits.htm#BOOST_PP_LIMIT_MAG">BOOST_PP_LIMIT_MAG</a>.</li>
<li>Using <a href="while.htm#BOOST_PP_WHILE">BOOST_PP_WHILE</a>() is a bit tricky. This is due to the C++
preprocessor limitations. It is recommended to take a look at the
implementations of the various PREPROCESSOR library primitives such as
<a href="arithmetic_add.htm#BOOST_PP_ADD">BOOST_PP_ADD</a>() for additional examples.</li>
</ul>
<P>Using <a href="while.htm#BOOST_PP_WHILE">BOOST_PP_WHILE</a>() is a bit tricky. This is due to the C++ preprocessor
limitations. It is recommended to take a look at the implementations of the
various PREPROCESSOR library primitives such as <a href="arithmetic_add.htm#BOOST_PP_ADD">BOOST_PP_ADD</a>() for
additional examples.</P>
<H3>Example</H3>
<UL>
<LI><a href="../../example/count_down.c">count_down.c</a>
<LI><a hreF="../../example/linear_fib.c">linear_fib.c</a>
</UL>
<H3>Implementation rationale</H3>
<UL>
<LI>The maximum iteration depth is greater than 2*<a href="limits.htm#BOOST_PP_LIMIT_MAG">BOOST_PP_LIMIT_MAG</a> to make
it possible to compute N*N functions.
</UL>
<h3>Example</h3>
<ul>
<li><a href="../../example/count_down.c">count_down.c</a></li>
<li><a href="../../example/linear_fib.c">linear_fib.c</a></li>
<li><a href="../../example/delay.c">delay.c</a></li>
</ul>
<hr>
<p>(C) Copyright Housemarque Oy 2002</p>
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