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53 lines
1.7 KiB
HTML
53 lines
1.7 KiB
HTML
<html>
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<head>
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<title>BOOST_PP_LIST_FIRST_N</title>
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<link rel="stylesheet" type="text/css" href="../styles.css">
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<script language="javascript" type="text/javascript" src="../scripts.js"></script>
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</head>
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<body onload="init('sample');">
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<div style="margin-left: 0px;">
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The <b>BOOST_PP_LIST_FIRST_N</b> macro expands to a <i>list</i> of the first <i>count</i> elements of a <i>list</i>.
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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_LIST_FIRST_N</b>(<i>count</i>, <i>list</i>)
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</div>
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<h4>Arguments</h4>
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<dl>
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<dt>count</dt>
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<dd>
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The number of elements to extract.
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</dd>
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<dt>list</dt>
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<dd>
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The <i>list</i> from which the elements are extracted.
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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 extracts <i>count</i> elements from the beginning of <i>list</i> and returns them as a <i>list</i>
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</div>
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<div>
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Previously, this macro could not be used inside <b>BOOST_PP_WHILE</b>.
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There is no longer any such restriction.
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It is more efficient, however, to use <b>BOOST_PP_LIST_FIRST_N_D</b> in such a situation.
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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="list_first_n_d.html">BOOST_PP_LIST_FIRST_N_D</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/list/first_n.hpp.html"><boost/preprocessor/list/first_n.hpp></a>
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</div>
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<h4><a class="local" onclick="toggle('sample');" onmouseover="change(this);" onmouseout="revert(this);">Sample Code</a></h4>
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<div id="sample"><pre>
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#include <boost/preprocessor/list/first_n.hpp>
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#define LIST (a, (b, (c, BOOST_PP_NIL)))
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BOOST_PP_LIST_FIRST_N(2, LIST) // expands to (a, (b, BOOST_PP_NIL))
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<pre></div>
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</body>
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</html>
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