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25<div class="section" lang="en">
26<div class="titlepage"><div><div><h3 class="title">
27<a name="hash.tutorial"></a> Tutorial</h3></div></div></div>
28<p>
29When using a hash index with <a href="../../../libs/multi_index/doc/index.html" target="_top">Boost.MultiIndex</a>, you don't need to do
30anything to use <code class="computeroutput"><a href="../boost/hash.html" title="Struct template hash">boost::hash</a></code> as it uses it by default.
31To find out how to use a user-defined type, read the
32<a href="custom.html" title=" Extending boost::hash for a custom data type">section on extending boost::hash for a custom data type</a>.</p>
33<p>
34If your standard library supplies its own implementation of the unordered
35associative containers and you wish to use
36<code class="computeroutput"><a href="../boost/hash.html" title="Struct template hash">boost::hash</a></code>, just use an extra template parameter:</p>
37<pre class="programlisting"><code class="literal"><span class="identifier">std</span><span class="special">::</span><span class="identifier">unordered_multiset</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</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="keyword">int</span><span class="special">&gt;</span><span class="special"> &gt;</span><span class="identifier">
38        set_of_ints</span><span class="special">;</span><span class="identifier">
39
40std</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><span class="identifier">
41        set_of_pairs</span><span class="special">;</span><span class="identifier">
42
43std</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></code></pre>
44<p>
45To use <code class="computeroutput"><a href="../boost/hash.html" title="Struct template hash">boost::hash</a></code> directly, create an instance and call it as a function:</p>
46<pre class="programlisting"><code class="literal"><span class="preprocessor">#include</span><span class="special"> &lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">hash</span><span class="special">/</span><span class="identifier">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span><span class="keyword">
47
48int</span><span class="identifier"> main</span><span class="special">()</span><span class="special">
49{</span>
50    <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><span class="identifier">
51
52    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><span class="special">
53}</span></code></pre>
54<p>
55If you wish to make use of the extensions, you will need to include the
56appropriate header (see the
57<a href="reference_.html#hash.reference.specification" title="">reference documentation</a> for the full list).</p>
58<pre class="programlisting"><code class="literal"><span class="preprocessor">#include</span><span class="special"> &lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">hash</span><span class="special">/</span><span class="identifier">pair</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span><span class="keyword">
59
60int</span><span class="identifier"> main</span><span class="special">()</span><span class="special">
61{</span>
62    <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><span class="identifier"> pair_hash</span><span class="special">;</span><span class="identifier">
63
64    std</span><span class="special">::</span><span class="identifier">size_t</span><span class="identifier"> h</span><span class="special"> =</span><span class="identifier"> pair_hash</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">make_pair</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="special">
65}</span></code></pre>
66<p>
67Or alternatively, include <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code> for the full library.</p>
68<p>
69For an example of generic use, here is a function to generate a vector
70containing the hashes of the elements of a container:</p>
71<pre class="programlisting"><code class="literal"><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><span class="identifier">
72std</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><span class="special">
73{</span><span class="identifier">
74    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><span class="identifier">
75    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>
76        <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><span class="keyword">
77
78    return</span><span class="identifier"> hashes</span><span class="special">;</span><span class="special">
79}</span></code></pre>
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83<td align="right"><small>Copyright © 2005 Daniel James</small></td>
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