1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Hashing</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="../operator.html" title="Operator"> 9<link rel="prev" href="comparison/greater_than_equal.html" title="greater than equal"> 10<link rel="next" href="../../container.html" title="Container"> 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="comparison/greater_than_equal.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../operator.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="../../container.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h4 class="title"> 27<a name="fusion.sequence.operator.hashing"></a><a class="link" href="hashing.html" title="Hashing">Hashing</a> 28</h4></div></div></div> 29<p> 30 Automatically create a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">hash</span></code> 31 conforming <code class="computeroutput"><span class="identifier">hash_value</span></code> function. 32 </p> 33<h6> 34<a name="fusion.sequence.operator.hashing.h0"></a> 35 <span class="phrase"><a name="fusion.sequence.operator.hashing.synopsis"></a></span><a class="link" href="hashing.html#fusion.sequence.operator.hashing.synopsis">Synopsis</a> 36 </h6> 37<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Seq</span><span class="special">></span> 38<span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> 39<span class="identifier">hash_value</span><span class="special">(</span><span class="identifier">Seq</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">seq</span><span class="special">);</span> 40</pre> 41<h6> 42<a name="fusion.sequence.operator.hashing.h1"></a> 43 <span class="phrase"><a name="fusion.sequence.operator.hashing.parameters"></a></span><a class="link" href="hashing.html#fusion.sequence.operator.hashing.parameters">Parameters</a> 44 </h6> 45<div class="informaltable"><table class="table"> 46<colgroup> 47<col> 48<col> 49<col> 50</colgroup> 51<thead><tr> 52<th> 53 <p> 54 Parameter 55 </p> 56 </th> 57<th> 58 <p> 59 Requirement 60 </p> 61 </th> 62<th> 63 <p> 64 Description 65 </p> 66 </th> 67</tr></thead> 68<tbody><tr> 69<td> 70 <p> 71 <code class="computeroutput"><span class="identifier">seq</span></code> 72 </p> 73 </td> 74<td> 75 <p> 76 Instance of <a class="link" href="../../sequence.html" title="Sequence">Sequence</a> 77 </p> 78 </td> 79<td> 80 <p> 81 <a class="link" href="../../sequence.html" title="Sequence">Sequence</a> to compute hash 82 value of 83 </p> 84 </td> 85</tr></tbody> 86</table></div> 87<p> 88 <span class="bold"><strong>Return type</strong></span>: <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span></code> 89 </p> 90<p> 91 <span class="bold"><strong>Requirements</strong></span>: 92 </p> 93<p> 94 For each element <code class="computeroutput"><span class="identifier">e</span></code> in sequence 95 <code class="computeroutput"><span class="identifier">seq</span></code>, <code class="computeroutput"><span class="identifier">hash_value</span><span class="special">(</span><span class="identifier">seq</span><span class="special">)</span></code> is a valid expression returning a type 96 that is convertible to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span></code>. 97 </p> 98<p> 99 <span class="bold"><strong>Semantics</strong></span>: Returns a combined hash value 100 for all elements of <code class="computeroutput"><span class="identifier">seq</span></code>. 101 </p> 102<h6> 103<a name="fusion.sequence.operator.hashing.h2"></a> 104 <span class="phrase"><a name="fusion.sequence.operator.hashing.header"></a></span><a class="link" href="hashing.html#fusion.sequence.operator.hashing.header">Header</a> 105 </h6> 106<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">sequence</span><span class="special">/</span><span class="identifier">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 107<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">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 108</pre> 109<h6> 110<a name="fusion.sequence.operator.hashing.h3"></a> 111 <span class="phrase"><a name="fusion.sequence.operator.hashing.example"></a></span><a class="link" href="hashing.html#fusion.sequence.operator.hashing.example">Example</a> 112 </h6> 113<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">include</span><span class="special">/</span><span class="identifier">equal_to</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 114<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">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 115<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">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 116<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">unordered_map</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 117 118<span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span> 119<span class="special">{</span> 120 <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">char</span><span class="special">></span> <span class="identifier">Vec</span><span class="special">;</span> 121 <span class="keyword">const</span> <span class="identifier">Vec</span> <span class="identifier">v</span> <span class="special">=</span> <span class="special">{</span><span class="number">42</span><span class="special">,</span> <span class="string">"Hello World"</span><span class="special">,</span> <span class="char">'t'</span><span class="special">};</span> 122 <span class="comment">// Compute a hash value directly.</span> 123 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"hash_value(v) = "</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">hash_value</span><span class="special">(</span><span class="identifier">v</span><span class="special">)</span> <span class="special"><<</span> <span class="char">'\n'</span><span class="special">;</span> 124 <span class="comment">// Or use it to create an unordered_map.</span> 125 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">unordered_map</span><span class="special"><</span><span class="identifier">Vec</span><span class="special">,</span> <span class="keyword">bool</span><span class="special">></span> <span class="identifier">map</span><span class="special">;</span> 126 <span class="identifier">map</span><span class="special">[</span><span class="identifier">v</span><span class="special">]</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">;</span> 127 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">map</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span> <span class="special">&&</span> <span class="identifier">map</span><span class="special">.</span><span class="identifier">count</span><span class="special">(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span> 128<span class="special">}</span> 129</pre> 130<h6> 131<a name="fusion.sequence.operator.hashing.h4"></a> 132 <span class="phrase"><a name="fusion.sequence.operator.hashing.example0"></a></span><a class="link" href="hashing.html#fusion.sequence.operator.hashing.example0">Example</a> 133 </h6> 134<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">include</span><span class="special">/</span><span class="identifier">define_struct</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 135<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">equal_to</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 136<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">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 137<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">unordered_set</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 138 139<span class="comment">// We would like to define a struct that we can form unordered_sets of.</span> 140<span class="identifier">BOOST_FUSION_DEFINE_STRUCT</span><span class="special">(</span> 141 <span class="special">(</span><span class="identifier">demo</span><span class="special">),</span> <span class="identifier">Key</span><span class="special">,</span> 142 <span class="special">(</span><span class="keyword">bool</span><span class="special">,</span> <span class="identifier">b</span><span class="special">)</span> 143 <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">s</span><span class="special">)</span> 144 <span class="special">(</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">i</span><span class="special">)</span> 145<span class="special">)</span> 146 147<span class="keyword">namespace</span> <span class="identifier">demo</span> <span class="special">{</span> 148 <span class="comment">// Make operator== and hash_value ADL accessible.</span> 149 <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fusion</span><span class="special">::</span><span class="keyword">operator</span><span class="special">==;</span> 150 <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">hash_value</span><span class="special">;</span> 151 <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">unordered_set</span><span class="special"><</span><span class="identifier">demo</span><span class="special">::</span><span class="identifier">Key</span><span class="special">></span> <span class="identifier">Set</span><span class="special">;</span> 152<span class="special">}</span> 153 154<span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span> 155<span class="special">{</span> 156 <span class="identifier">demo</span><span class="special">::</span><span class="identifier">Set</span> <span class="identifier">set</span><span class="special">;</span> 157 <span class="identifier">demo</span><span class="special">::</span><span class="identifier">Key</span> <span class="identifier">key</span><span class="special">;</span> 158 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">set</span><span class="special">.</span><span class="identifier">count</span><span class="special">(</span><span class="identifier">key</span><span class="special">)</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span> 159<span class="special">}</span> 160</pre> 161<h6> 162<a name="fusion.sequence.operator.hashing.h5"></a> 163 <span class="phrase"><a name="fusion.sequence.operator.hashing.see_also"></a></span><a class="link" href="hashing.html#fusion.sequence.operator.hashing.see_also">See 164 also</a> 165 </h6> 166<p> 167 <a href="http://www.boost.org/doc/html/hash.html" target="_top">Boost.ContainerHash 168 Library</a> 169 </p> 170</div> 171<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 172<td align="left"></td> 173<td align="right"><div class="copyright-footer">Copyright © 2001-2006, 2011, 2012 Joel de Guzman, 174 Dan Marsden, Tobias Schwinger<p> 175 Distributed under the Boost Software License, Version 1.0. (See accompanying 176 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>) 177 </p> 178</div></td> 179</tr></table> 180<hr> 181<div class="spirit-nav"> 182<a accesskey="p" href="comparison/greater_than_equal.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../operator.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="../../container.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 183</div> 184</body> 185</html> 186
