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1<html>
2<head>
3<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
4<title> Tutorial</title>
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7<link rel="start" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset">
8<link rel="up" href="../hash.html" title="Chapter 7. Boost.Functional/Hash">
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26<div class="titlepage"><div><div><h2 class="title" style="clear: both">
27<a name="hash.tutorial"></a> Tutorial</h2></div></div></div>
28<p>
29      When using a hash index with <a href="../../../libs/multi_index/doc/index.html" target="_top">Boost.MultiIndex</a>,
30      you don't need to do anything to use <code class="computeroutput"><a href="../boost/hash.html" title="Struct template hash">boost::hash</a></code>
31      as it uses it by default. To find out how to use a user-defined type, read
32      the <a href="custom.html" title=" Extending boost::hash for a custom data type">section on extending boost::hash for a custom
33      data type</a>.
34    </p>
35<p>
36      If your standard library supplies its own implementation of the unordered associative
37      containers and you wish to use <code class="computeroutput"><a href="../boost/hash.html" title="Struct template hash">boost::hash</a></code>,
38      just use an extra template parameter:
39    </p>
40<pre class="programlisting">
41<span class="identifier">std</span><span class="special">::</span><span class="identifier">unordered_multiset</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <code class="computeroutput"><a href="../boost/hash.html" title="Struct template hash">boost::hash</a></code><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="special">&gt;</span>
42        <span class="identifier">set_of_ints</span><span class="special">;</span>
43
44<span class="identifier">std</span><span class="special">::</span><span class="identifier">unordered_set</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">&gt;,</span> <code class="computeroutput"><a href="../boost/hash.html" title="Struct template hash">boost::hash</a></code><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">&gt;</span> <span class="special">&gt;</span>
45        <span class="identifier">set_of_pairs</span><span class="special">;</span>
46
47<span class="identifier">std</span><span class="special">::</span><span class="identifier">unordered_map</span><span class="special">&lt;</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> <code class="computeroutput"><a href="../boost/hash.html" title="Struct template hash">boost::hash</a></code><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">map_int_to_string</span><span class="special">;</span>
48</pre>
49<p>
50      To use <code class="computeroutput"><a href="../boost/hash.html" title="Struct template hash">boost::hash</a></code> directly, create
51      an instance and call it as a function:
52    </p>
53<pre class="programlisting">
54<span class="preprocessor">#include</span> <span class="special">&lt;</span><code class="computeroutput"><a href="reference.html#header.boost.functional.hash.hpp" title="Header &lt;boost/functional/hash.hpp&gt;">boost/functional/hash.hpp</a></code><span class="special">&gt;</span>
55
56<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
57<span class="special">{</span>
58    <code class="computeroutput"><a href="../boost/hash.html" title="Struct template hash">boost::hash</a></code><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="identifier">string_hash</span><span class="special">;</span>
59
60    <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">h</span> <span class="special">=</span> <span class="identifier">string_hash</span><span class="special">(</span><span class="string">"Hash me"</span><span class="special">);</span>
61<span class="special">}</span>
62</pre>
63<p>
64      For an example of generic use, here is a function to generate a vector containing
65      the hashes of the elements of a container:
66    </p>
67<pre class="programlisting">
68<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Container</span><span class="special">&gt;</span>
69<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span> <span class="identifier">get_hashes</span><span class="special">(</span><span class="identifier">Container</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">)</span>
70<span class="special">{</span>
71    <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span> <span class="identifier">hashes</span><span class="special">;</span>
72    <span class="identifier">std</span><span class="special">::</span><span class="identifier">transform</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">insert_iterator</span><span class="special">(</span><span class="identifier">hashes</span><span class="special">),</span>
73        <code class="computeroutput"><a href="../boost/hash.html" title="Struct template hash">boost::hash</a></code><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Container</span><span class="special">::</span><span class="identifier">value_type</span><span class="special">&gt;());</span>
74
75    <span class="keyword">return</span> <span class="identifier">hashes</span><span class="special">;</span>
76<span class="special">}</span>
77</pre>
78</div>
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80<td align="left"></td>
81<td align="right"><small>Copyright © 2005, 2006 Daniel James</small></td>
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