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7<title>The MPL Reference Manual: copy_if</title>
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11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./copy.html" class="navigation-link">Prev</a>&nbsp;<a href="./transform.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./copy.html" class="navigation-link">Back</a>&nbsp;<a href="./transform.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./transformation-algorithms.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
12<td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./algorithms.html" class="navigation-link">Algorithms</a> / <a href="./transformation-algorithms.html" class="navigation-link">Transformation Algorithms</a> / <a href="./copy-if.html" class="navigation-link">copy_if</a></td>
13</tr></table><div class="header-separator"></div>
14<div class="section" id="copy-if">
15<h1><a class="toc-backref" href="./transformation-algorithms.html#id415" name="copy-if">copy_if</a></h1>
16<div class="section" id="transformation-copy-synopsis">
17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
18<pre class="literal-block">
19template&lt;
20      typename Sequence
21    , typename Pred
22    , typename In = <em>unspecified</em>
23    &gt;
24struct <a href="./copy-if.html" class="identifier">copy_if</a>
25{
26    typedef <em>unspecified</em> type;
27};
28</pre>
29</div>
30<div class="section" id="transformation-copy-description">
31<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
32<p>Returns a filtered copy of the original sequence containing the elements that satisfy
33the predicate <tt class="literal"><span class="pre">Pred</span></tt>.</p>
34<p>[<em>Note:</em> This wording applies to a no-inserter version(s) of the algorithm. See the
35<cite>Expression semantics</cite> subsection for a precise specification of the algorithm's
36details in all cases — <em>end note</em>]</p>
37</div>
38<div class="section" id="transformation-copy-header">
39<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
40<pre class="literal-block">
41#include &lt;<a href="../../../../boost/mpl/copy_if.hpp" class="header">boost/mpl/copy_if.hpp</a>&gt;
42</pre>
43</div>
44<div class="section" id="transformation-copy-model-of">
45<h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3>
46<p><a class="reference" href="./reversible-algorithm.html">Reversible Algorithm</a></p>
47</div>
48<div class="section" id="transformation-copy-parameters">
49<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
50<table border="1" class="table">
51<colgroup>
52<col width="19%" />
53<col width="40%" />
54<col width="40%" />
55</colgroup>
56<thead valign="bottom">
57<tr><th>Parameter</th>
58<th>Requirement</th>
59<th>Description</th>
60</tr>
61</thead>
62<tbody valign="top">
63<tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td>
64<td><a class="reference" href="./forward-sequence.html">Forward Sequence</a></td>
65<td>A sequence to copy.</td>
66</tr>
67<tr><td><tt class="literal"><span class="pre">Pred</span></tt></td>
68<td>Unary <a class="reference" href="./lambda-expression.html">Lambda Expression</a></td>
69<td>A copying condition.</td>
70</tr>
71<tr><td><tt class="literal"><span class="pre">In</span></tt></td>
72<td><a class="reference" href="./inserter.html">Inserter</a></td>
73<td>An inserter.</td>
74</tr>
75</tbody>
76</table>
77</div>
78<div class="section" id="transformation-copy-expression-semantics">
79<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
80<p>The semantics of an expression are defined only
81where they differ from, or are not defined in <a class="reference" href="./reversible-algorithm.html">Reversible Algorithm</a>.</p>
82<p>For any <a class="reference" href="./forward-sequence.html">Forward Sequence</a> <tt class="literal"><span class="pre">s</span></tt>, an unary <a class="reference" href="./lambda-expression.html">Lambda Expression</a> <tt class="literal"><span class="pre">pred</span></tt>, and
83an <a class="reference" href="./inserter.html">Inserter</a> <tt class="literal"><span class="pre">in</span></tt>:</p>
84<pre class="literal-block">
85typedef <a href="./copy-if.html" class="identifier">copy_if</a>&lt;s,pred,in&gt;::type r;
86</pre>
87<table class="field-list" frame="void" rules="none">
88<col class="field-name" />
89<col class="field-body" />
90<tbody valign="top">
91<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type.</td>
92</tr>
93<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
94<pre class="last literal-block">
95typedef <a href="./lambda.html" class="identifier">lambda</a>&lt;pred&gt;::type p;
96typedef <a href="./lambda.html" class="identifier">lambda</a>&lt;in::operation&gt;::type op;
97
98typedef <a href="./fold.html" class="identifier">fold</a>&lt;
99      s
100    , in::state
101    , <a href="./eval-if.html" class="identifier">eval_if</a>&lt;
102          <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">1</span></tt>&lt;p,_2&gt;
103        , <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">2</span></tt>&lt;op,_1,_2&gt;
104        , <a href="./identity.html" class="identifier">identity</a>&lt;_1&gt;
105        &gt;
106    &gt;::type r;
107</pre>
108</td>
109</tr>
110</tbody>
111</table>
112</div>
113<div class="section" id="transformation-copy-complexity">
114<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
115<p>Linear. Exactly <tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a>&lt;s&gt;::value</span></tt> applications of <tt class="literal"><span class="pre">pred</span></tt>, and at
116most <tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a>&lt;s&gt;::value</span></tt> applications of <tt class="literal"><span class="pre">in::operation</span></tt>.</p>
117</div>
118<div class="section" id="transformation-copy-example">
119<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
120<pre class="literal-block">
121typedef <a href="./copy-if.html" class="identifier">copy_if</a>&lt;
122      <a href="./range-c.html" class="identifier">range_c</a>&lt;int,0,10&gt;
123    , <a href="./less.html" class="identifier">less</a>&lt; _1, <a href="./int.html" class="identifier">int_</a>&lt;5&gt; &gt;
124    , <a href="./back-inserter.html" class="identifier">back_inserter</a>&lt; <a href="./vector.html" class="identifier">vector</a>&lt;&gt; &gt;
125    &gt;::type result;
126
127<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( <a href="./size.html" class="identifier">size</a>&lt;result&gt;::value, ==, 5 );
128<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./equal.html" class="identifier">equal</a>&lt;result,<a href="./range-c.html" class="identifier">range_c</a>&lt;int,0,5&gt; > ));
129</pre>
130</div>
131<div class="section" id="transformation-copy-see-also">
132<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
133<p><a class="reference" href="./transformation-algorithms.html">Transformation Algorithms</a>, <a class="reference" href="./reversible-algorithm.html">Reversible Algorithm</a>, <a class="refentry reference" href="./reverse-copy-if.html"><tt class="refentry literal"><span class="pre">reverse_copy_if</span></tt></a>, <a class="refentry reference" href="./copy.html"><tt class="refentry literal"><span class="pre">copy</span></tt></a>, <a class="refentry reference" href="./remove-if.html"><tt class="refentry literal"><span class="pre">remove_if</span></tt></a>, <a class="refentry reference" href="./replace-if.html"><tt class="refentry literal"><span class="pre">replace_if</span></tt></a></p>
134<!-- modtime: November 13, 2004 01:54:56 +0000 -->
135<!-- Algorithms/Transformation Algorithms//transform |30 -->
136</div>
137</div>
138
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