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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="hash.tutorial"></a><a class="link" href="tutorial.html" title="Tutorial">Tutorial</a> |
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| <p> |
| When using a hash index with <a href="../../../libs/multi_index/doc/index.html" target="_top">Boost.MultiIndex</a>, |
| you don't need to do anything to use <code class="computeroutput"><a class="link" href="../boost/hash.html" title="Struct template hash">boost::hash</a></code> |
| as it uses it by default. To find out how to use a user-defined type, read |
| the <a class="link" href="custom.html" title="Extending boost::hash for a custom data type">section on extending boost::hash for a custom |
| data type</a>. |
| </p> |
| <p> |
| If your standard library supplies its own implementation of the unordered associative |
| containers and you wish to use <code class="computeroutput"><a class="link" href="../boost/hash.html" title="Struct template hash">boost::hash</a></code>, |
| just use an extra template parameter: |
| </p> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">unordered_multiset</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <code class="computeroutput"><a class="link" href="../boost/hash.html" title="Struct template hash">boost::hash</a></code><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">></span> |
| <span class="identifier">set_of_ints</span><span class="special">;</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">unordered_set</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">>,</span> <code class="computeroutput"><a class="link" href="../boost/hash.html" title="Struct template hash">boost::hash</a></code><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</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="special">></span> |
| <span class="identifier">set_of_pairs</span><span class="special">;</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">unordered_map</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> <code class="computeroutput"><a class="link" href="../boost/hash.html" title="Struct template hash">boost::hash</a></code><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">></span> <span class="identifier">map_int_to_string</span><span class="special">;</span> |
| </pre> |
| <p> |
| To use <code class="computeroutput"><a class="link" href="../boost/hash.html" title="Struct template hash">boost::hash</a></code> directly, create |
| an instance and call it as a function: |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><code class="computeroutput"><a class="link" href="reference.html#header.boost.functional.hash_hpp" title="Header <boost/functional/hash.hpp>">boost/functional/hash.hpp</a></code><span class="special">></span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <code class="computeroutput"><a class="link" href="../boost/hash.html" title="Struct template hash">boost::hash</a></code><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">string_hash</span><span class="special">;</span> |
| |
| <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> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| For an example of generic use, here is a function to generate a vector containing |
| the hashes of the elements of a container: |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Container</span><span class="special">></span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">></span> <span class="identifier">get_hashes</span><span class="special">(</span><span class="identifier">Container</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">></span> <span class="identifier">hashes</span><span class="special">;</span> |
| <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> |
| <code class="computeroutput"><a class="link" href="../boost/hash.html" title="Struct template hash">boost::hash</a></code><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Container</span><span class="special">::</span><span class="identifier">value_type</span><span class="special">>());</span> |
| |
| <span class="keyword">return</span> <span class="identifier">hashes</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
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| <td align="right"><div class="copyright-footer">Copyright © 2005-2008 Daniel |
| James<p> |
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