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<title>Chapter 12. Boost.Functional/Hash</title>
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<div><h2 class="title">
<a name="hash"></a>Chapter 12. Boost.Functional/Hash</h2></div>
<div><div class="author"><h3 class="author">
<span class="firstname">Daniel</span> <span class="surname">James</span>
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<div><p class="copyright">Copyright © 2005-2008 Daniel
James</p></div>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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>)
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<p><b>Table of Contents</b></p>
<dl class="toc">
<dt><span class="section"><a href="hash.html#hash.intro">Introduction</a></span></dt>
<dt><span class="section"><a href="hash/tutorial.html">Tutorial</a></span></dt>
<dt><span class="section"><a href="hash/custom.html">Extending boost::hash for a custom data type</a></span></dt>
<dt><span class="section"><a href="hash/combine.html">Combining hash values</a></span></dt>
<dt><span class="section"><a href="hash/portability.html">Portability</a></span></dt>
<dt><span class="section"><a href="hash/disable.html">Disabling The Extensions</a></span></dt>
<dt><span class="section"><a href="hash/changes.html">Change Log</a></span></dt>
<dt><span class="section"><a href="hash/rationale.html">Rationale</a></span></dt>
<dt><span class="section"><a href="hash/reference.html">Reference</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="hash/reference.html#hash.reference.specification"></a></span></dt>
<dt><span class="section"><a href="hash/reference.html#header.boost.functional.hash_hpp">Header <boost/functional/hash.hpp></a></span></dt>
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<dt><span class="section"><a href="hash/links.html">Links</a></span></dt>
<dt><span class="section"><a href="hash/acknowledgements.html">Acknowledgements</a></span></dt>
</dl>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="hash.intro"></a><a class="link" href="hash.html#hash.intro" title="Introduction">Introduction</a>
</h2></div></div></div>
<p>
<code class="computeroutput"><a class="link" href="boost/hash.html" title="Struct template hash">boost::hash</a></code> is an implementation of
the <a href="http://en.wikipedia.org/wiki/Hash_function" target="_top">hash function</a>
object specified by the <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">Draft
Technical Report on C++ Library Extensions</a> (TR1). It is the default
hash function for <a class="link" href="unordered.html" title="Chapter 38. Boost.Unordered">Boost.Unordered</a>, <a class="link" href="intrusive/unordered_set_unordered_multiset.html" title="Semi-Intrusive unordered associative containers: unordered_set, unordered_multiset">Boost.Intrusive</a>'s
unordered associative containers, and <a href="../../libs/multi_index/doc/index.html" target="_top">Boost.MultiIndex</a>'s
hash indicies and <a href="../../libs/bimap/index.html" target="_top">Boost.Bimap</a>'s
<code class="computeroutput"><span class="identifier">unordered_set_of</span></code>.
</p>
<p>
As it is compliant with <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">TR1</a>,
it will work with:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
integers
</li>
<li class="listitem">
floats
</li>
<li class="listitem">
pointers
</li>
<li class="listitem">
strings
</li>
</ul></div>
<p>
It also implements the extension proposed by Peter Dimov in issue 6.18 of the
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1837.pdf" target="_top">Library
Extension Technical Report Issues List</a> (page 63), this adds support
for:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
arrays
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span></code>
</li>
<li class="listitem">
the standard containers.
</li>
<li class="listitem">
extending <code class="computeroutput"><a class="link" href="boost/hash.html" title="Struct template hash">boost::hash</a></code> for custom
types.
</li>
</ul></div>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
This hash function is designed to be used in containers based on the STL
and is not suitable as a general purpose hash function. For more details
see the <a class="link" href="hash/rationale.html" title="Rationale">rationale</a>.
</p></td></tr>
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<td align="left"><p><small>Last revised: December 14, 2015 at 09:17:40 GMT</small></p></td>
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