preprocessor/doc/reference/for_8hpp.html

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<hr><h1>for.hpp File Reference</h1><table border=0 cellpadding=0 cellspacing=0>
<tr><td colspan=2><br><h2>Defines</h2></td></tr>
<tr><td nowrap align=right valign=top>#define&nbsp;</td><td valign=bottom><a class="el" href="for_8hpp.html#a0">BOOST_PP_FOR</a>(X, C, F, I)</td></tr>
<tr><td>&nbsp;</td><td><font size=-1><em>Repeats I(R,X) and iterates F(R,X) while C(R,X) is true.</em> <a href="#a0">More...</a><em></em></font><br><br></td></tr>
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<hr><a name="_details"></a><h2>Detailed Description</h2>
 <a href="../../../../boost/preprocessor/for.hpp">Click here to see the header.</a>
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<hr><h2>Define Documentation</h2>
<a name="a0" doxytag="for.hpp::BOOST_PP_FOR"></a><p>
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          <td class="md" nowrap valign="top"> #define BOOST_PP_FOR</td>
          <td class="md" valign="top">(&nbsp;</td>
          <td class="md" nowrap valign="top">X,         <tr>
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          <td class="md" nowrap>C,         <tr>
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          <td class="md" nowrap>F,         <tr>
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          <td class="md" nowrap>I&nbsp;</td>
          <td class="mdname1" valign="top" nowrap>&nbsp;          </td>
          <td class="md" valign="top">)&nbsp;</td>
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<p>
Repeats I(R,X) and iterates F(R,X) while C(R,X) is true.
<p>
In other words, expands to the sequence:
<p>
<pre><div class="fragment"><pre>
  I(R,X)  I(R,F(R,X))  I(R,F(R,F(R,X)))  ...  I(R,F(R,F(...F(R,X)...)))
</pre></div></pre>
<p>
The length of the sequence is determined by C(R,X).
<p>
<h3>Legend</h3>

<p>
<b>X</b> is the current state of iteration. The state is usually a tuple.
<p>
<b>C</b> is the condition for iteration. It must expand to a decimal integer literal.
<p>
<b>F</b> is the iterated macro. Note that if the state is a tuple, then F(R,X) usually expands to a tuple of the same number of elements.
<p>
<b>I</b> is the state instantiation macro.
<p>
<b>R</b> is the recursion depth and should only be used as a parameter to other macros implemented using <a class="el" href="for_8hpp.html#a0">BOOST_PP_FOR</a>() or for invoking BOOST_PP_FOR#R() directly. For each macro implemented using <a class="el" href="for_8hpp.html#a0">BOOST_PP_FOR</a>(), there is a version of the macro, distinguished by the _R suffix, 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.
<p>
<h3><a class="el" href="repeat_8hpp.html#a0">BOOST_PP_REPEAT</a>() vs <a class="el" href="for_8hpp.html#a0">BOOST_PP_FOR</a>()</h3>

<p>
<a class="el" href="for_8hpp.html#a0">BOOST_PP_FOR</a>() is a generalization of <a class="el" href="repeat_8hpp.html#a0">BOOST_PP_REPEAT</a>(). This means that <a class="el" href="repeat_8hpp.html#a0">BOOST_PP_REPEAT</a>() can be implemented using <a class="el" href="for_8hpp.html#a0">BOOST_PP_FOR</a>(). Unfortunately, <a class="el" href="for_8hpp.html#a0">BOOST_PP_FOR</a>() is slower than <a class="el" href="repeat_8hpp.html#a0">BOOST_PP_REPEAT</a>(). In addition, <a class="el" href="repeat_8hpp.html#a0">BOOST_PP_REPEAT</a>() was introduced earlier, is generally easier to use, and is still quite useful on its own.
<p>
<h3>2D and 3D repetition</h3>

<p>
<a class="el" href="for_8hpp.html#a0">BOOST_PP_FOR</a>() can be used for multidimensional repetition simply by invoking BOOST_PP_FOR#R() directly.     </td>
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