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10<title>The MPL Reference Manual: find_if</title>
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13<body class="docframe refmanual">
14<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./find.html" class="navigation-link">Prev</a>&nbsp;<a href="./contains.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./find.html" class="navigation-link">Back</a>&nbsp;<a href="./contains.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./querying-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>
15<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="./querying-algorithms.html" class="navigation-link">Querying Algorithms</a> / <a href="./find-if.html" class="navigation-link">find_if</a></td>
16</tr></table><div class="header-separator"></div>
17<div class="section" id="find-if">
18<h1><a class="toc-backref" href="./querying-algorithms.html#id404" name="find-if">find_if</a></h1>
19<div class="section" id="querying-find-synopsis">
20<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
21<pre class="literal-block">
22template&lt;
23      typename Sequence
24    , typename Pred
25    &gt;
26struct <a href="./find-if.html" class="identifier">find_if</a>
27{
28    typedef <em>unspecified</em> type;
29};
30</pre>
31</div>
32<div class="section" id="querying-find-description">
33<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
34<p>Returns an iterator to the first element in <tt class="literal"><span class="pre">Sequence</span></tt> that satisfies
35the predicate <tt class="literal"><span class="pre">Pred</span></tt>.</p>
36</div>
37<div class="section" id="querying-find-header">
38<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
39<pre class="literal-block">
40#include &lt;<a href="../../../../boost/mpl/find_if.hpp" class="header">boost/mpl/find_if.hpp</a>&gt;
41</pre>
42</div>
43<div class="section" id="querying-find-parameters">
44<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
45<table border="1" class="table">
46<colgroup>
47<col width="19%" />
48<col width="38%" />
49<col width="43%" />
50</colgroup>
51<thead valign="bottom">
52<tr><th>Parameter</th>
53<th>Requirement</th>
54<th>Description</th>
55</tr>
56</thead>
57<tbody valign="top">
58<tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td>
59<td><a class="reference" href="./forward-sequence.html">Forward Sequence</a></td>
60<td>A sequence to search in.</td>
61</tr>
62<tr><td><tt class="literal"><span class="pre">Pred</span></tt></td>
63<td>Unary <a class="reference" href="./lambda-expression.html">Lambda Expression</a></td>
64<td>A search condition.</td>
65</tr>
66</tbody>
67</table>
68</div>
69<div class="section" id="querying-find-expression-semantics">
70<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
71<p>For any <a class="reference" href="./forward-sequence.html">Forward Sequence</a> <tt class="literal"><span class="pre">s</span></tt> and unary <a class="reference" href="./lambda-expression.html">Lambda Expression</a> <tt class="literal"><span class="pre">pred</span></tt>:</p>
72<pre class="literal-block">
73typedef <a href="./find-if.html" class="identifier">find_if</a>&lt;s,pred&gt;::type i;
74</pre>
75<table class="field-list" frame="void" rules="none">
76<col class="field-name" />
77<col class="field-body" />
78<tbody valign="top">
79<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><a class="reference" href="./forward-iterator.html">Forward Iterator</a>.</td>
80</tr>
81<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first"><tt class="literal"><span class="pre">i</span></tt> is the first iterator in the range [<tt class="literal"><span class="pre"><a href="./begin.html" class="identifier">begin</a>&lt;s&gt;::type</span></tt>, <tt class="literal"><span class="pre"><a href="./end.html" class="identifier">end</a>&lt;s&gt;::type</span></tt>) such that</p>
82<pre class="literal-block">
83<a href="./apply.html" class="identifier">apply</a>&lt; pred,<a href="./deref.html" class="identifier">deref</a>&lt;i&gt;::type &gt;::type::value == true
84</pre>
85<p class="last">If no such iterator exists, <tt class="literal"><span class="pre">i</span></tt> is identical to <tt class="literal"><span class="pre"><a href="./end.html" class="identifier">end</a>&lt;s&gt;::type</span></tt>.</p>
86</td>
87</tr>
88</tbody>
89</table>
90</div>
91<div class="section" id="querying-find-complexity">
92<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
93<p>Linear. At most <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>.</p>
94</div>
95<div class="section" id="querying-find-example">
96<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
97<pre class="literal-block">
98typedef <a href="./vector.html" class="identifier">vector</a>&lt;char,int,unsigned,long,unsigned long&gt; types;
99typedef <a href="./find-if.html" class="identifier">find_if</a>&lt;types, is_same&lt;_1,unsigned&gt; &gt;::type iter;
100
101<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; <a href="./deref.html" class="identifier">deref</a>&lt;iter&gt;::type, unsigned &gt; ));
102<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( iter::pos::value, ==, 2 );
103</pre>
104</div>
105<div class="section" id="querying-find-see-also">
106<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
107<p><a class="reference" href="./querying-algorithms.html">Querying Algorithms</a>, <a class="refentry reference" href="./find.html"><tt class="refentry literal"><span class="pre">find</span></tt></a>, <a class="refentry reference" href="./count-if.html"><tt class="refentry literal"><span class="pre">count_if</span></tt></a>, <a class="refentry reference" href="./lower-bound.html"><tt class="refentry literal"><span class="pre">lower_bound</span></tt></a></p>
108<!-- modtime: November 10, 2004 04:42:05 +0000 -->
109<!-- Algorithms/Querying Algorithms//contains |30 -->
110</div>
111</div>
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