1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>count_if</title> 5<link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../../index.html" title="Chapter 1. Fusion 2.2"> 8<link rel="up" href="../functions.html" title="Functions"> 9<link rel="prev" href="count.html" title="count"> 10<link rel="next" href="../metafunctions.html" title="Metafunctions"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="count.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../functions.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../metafunctions.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h5 class="title"> 27<a name="fusion.algorithm.query.functions.count_if"></a><a class="link" href="count_if.html" title="count_if">count_if</a> 28</h5></div></div></div> 29<h6> 30<a name="fusion.algorithm.query.functions.count_if.h0"></a> 31 <span class="phrase"><a name="fusion.algorithm.query.functions.count_if.description"></a></span><a class="link" href="count_if.html#fusion.algorithm.query.functions.count_if.description">Description</a> 32 </h6> 33<p> 34 Returns the number of elements within a sequence with a type for which 35 a given unary function object evaluates to <code class="computeroutput"><span class="keyword">true</span></code>. 36 </p> 37<h6> 38<a name="fusion.algorithm.query.functions.count_if.h1"></a> 39 <span class="phrase"><a name="fusion.algorithm.query.functions.count_if.synopsis"></a></span><a class="link" href="count_if.html#fusion.algorithm.query.functions.count_if.synopsis">Synopsis</a> 40 </h6> 41<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> 42 <span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">,</span> 43 <span class="keyword">typename</span> <span class="identifier">F</span> 44 <span class="special">></span> 45<span class="keyword">typename</span> <a class="link" href="../metafunctions/count_if.html" title="count_if"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">count_if</span></code></a><span class="special"><</span><span class="identifier">Sequence</span><span class="special">,</span> <span class="identifier">F</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">count_if</span><span class="special">(</span> 46 <span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">seq</span><span class="special">,</span> <span class="identifier">F</span> <span class="identifier">f</span><span class="special">);</span> 47</pre> 48<div class="table"> 49<a name="fusion.algorithm.query.functions.count_if.t0"></a><p class="title"><b>Table 1.58. Parameters</b></p> 50<div class="table-contents"><table class="table" summary="Parameters"> 51<colgroup> 52<col> 53<col> 54<col> 55</colgroup> 56<thead><tr> 57<th> 58 <p> 59 Parameter 60 </p> 61 </th> 62<th> 63 <p> 64 Requirement 65 </p> 66 </th> 67<th> 68 <p> 69 Description 70 </p> 71 </th> 72</tr></thead> 73<tbody> 74<tr> 75<td> 76 <p> 77 <code class="computeroutput"><span class="identifier">seq</span></code> 78 </p> 79 </td> 80<td> 81 <p> 82 A model of <a class="link" href="../../../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward 83 Sequence</a>, <code class="computeroutput"><span class="identifier">f</span><span class="special">(</span><span class="identifier">e</span><span class="special">)</span></code> is a valid expression, convertible 84 to <code class="computeroutput"><span class="keyword">bool</span></code>, for each 85 element <code class="computeroutput"><span class="identifier">e</span></code> in 86 <code class="computeroutput"><span class="identifier">seq</span></code> 87 </p> 88 </td> 89<td> 90 <p> 91 The sequence to search 92 </p> 93 </td> 94</tr> 95<tr> 96<td> 97 <p> 98 <code class="computeroutput"><span class="identifier">f</span></code> 99 </p> 100 </td> 101<td> 102 <p> 103 A unary function object 104 </p> 105 </td> 106<td> 107 <p> 108 The search predicate 109 </p> 110 </td> 111</tr> 112</tbody> 113</table></div> 114</div> 115<br class="table-break"><h6> 116<a name="fusion.algorithm.query.functions.count_if.h2"></a> 117 <span class="phrase"><a name="fusion.algorithm.query.functions.count_if.expression_semantics"></a></span><a class="link" href="count_if.html#fusion.algorithm.query.functions.count_if.expression_semantics">Expression 118 Semantics</a> 119 </h6> 120<pre class="programlisting"><a class="link" href="count_if.html" title="count_if"><code class="computeroutput"><span class="identifier">count_if</span></code></a><span class="special">(</span><span class="identifier">seq</span><span class="special">,</span> <span class="identifier">f</span><span class="special">)</span> 121</pre> 122<p> 123 <span class="bold"><strong>Return type</strong></span>: <code class="computeroutput"><span class="keyword">int</span></code> 124 </p> 125<p> 126 <span class="bold"><strong>Semantics</strong></span>: Returns the number of elements 127 in <code class="computeroutput"><span class="identifier">seq</span></code> where <code class="computeroutput"><span class="identifier">f</span></code> evaluates to <code class="computeroutput"><span class="keyword">true</span></code>. 128 </p> 129<h6> 130<a name="fusion.algorithm.query.functions.count_if.h3"></a> 131 <span class="phrase"><a name="fusion.algorithm.query.functions.count_if.complexity"></a></span><a class="link" href="count_if.html#fusion.algorithm.query.functions.count_if.complexity">Complexity</a> 132 </h6> 133<p> 134 Linear. At most <code class="computeroutput"><a class="link" href="../../../sequence/intrinsic/metafunctions/size.html" title="size"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">size</span></code></a><span class="special"><</span><span class="identifier">Sequence</span><span class="special">>::</span><span class="identifier">value</span></code> comparisons. 135 </p> 136<h6> 137<a name="fusion.algorithm.query.functions.count_if.h4"></a> 138 <span class="phrase"><a name="fusion.algorithm.query.functions.count_if.header"></a></span><a class="link" href="count_if.html#fusion.algorithm.query.functions.count_if.header">Header</a> 139 </h6> 140<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">algorithm</span><span class="special">/</span><span class="identifier">query</span><span class="special">/</span><span class="identifier">count_if</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 141<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">count_if</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 142</pre> 143<h6> 144<a name="fusion.algorithm.query.functions.count_if.h5"></a> 145 <span class="phrase"><a name="fusion.algorithm.query.functions.count_if.example"></a></span><a class="link" href="count_if.html#fusion.algorithm.query.functions.count_if.example">Example</a> 146 </h6> 147<pre class="programlisting"><span class="keyword">const</span> <a class="link" href="../../../container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a><span class="special"><</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">vec</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="number">2</span><span class="special">,</span><span class="number">3</span><span class="special">);</span> 148<span class="identifier">assert</span><span class="special">(</span><a class="link" href="count_if.html" title="count_if"><code class="computeroutput"><span class="identifier">count_if</span></code></a><span class="special">(</span><span class="identifier">vec</span><span class="special">,</span><span class="identifier">odd</span><span class="special">())</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span> 149</pre> 150</div> 151<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 152<td align="left"></td> 153<td align="right"><div class="copyright-footer">Copyright © 2001-2006, 2011, 2012 Joel de Guzman, 154 Dan Marsden, Tobias Schwinger<p> 155 Distributed under the Boost Software License, Version 1.0. (See accompanying 156 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 157 </p> 158</div></td> 159</tr></table> 160<hr> 161<div class="spirit-nav"> 162<a accesskey="p" href="count.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../functions.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../metafunctions.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 163</div> 164</body> 165</html> 166
