1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>Map and multimap-like interface for associative containers</title> 6<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../intrusive.html" title="Chapter 19. Boost.Intrusive"> 10<link rel="prev" href="unordered_set_unordered_multiset.html" title="Semi-Intrusive unordered associative containers: unordered_set, unordered_multiset"> 11<link rel="next" href="avl_set_multiset.html" title="Intrusive avl tree based associative containers: avl_set, avl_multiset and avltree"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> 16<td align="center"><a href="../../../index.html">Home</a></td> 17<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> 18<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 19<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 20<td align="center"><a href="../../../more/index.htm">More</a></td> 21</tr></table> 22<hr> 23<div class="spirit-nav"> 24<a accesskey="p" href="unordered_set_unordered_multiset.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../intrusive.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="avl_set_multiset.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 25</div> 26<div class="section"> 27<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 28<a name="intrusive.map_multimap"></a><a class="link" href="map_multimap.html" title="Map and multimap-like interface for associative containers">Map and multimap-like interface 29 for associative containers</a> 30</h2></div></div></div> 31<p> 32 Implementing map-like intrusive containers is not a trivial task as STL's 33 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span></code> and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">multimap</span></code> 34 containers store copies of a <code class="computeroutput"><span class="identifier">value_type</span></code> 35 which is defined as <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">key_type</span><span class="special">,</span> <span class="identifier">mapped_type</span><span class="special">></span></code>. In order to reproduce this interface in 36 <span class="bold"><strong>Boost.Intrusive</strong></span> it shall require that objects 37 stored in the intrusive containers contain that <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span></code> member 38 with <code class="computeroutput"><span class="identifier">pair</span><span class="special">.</span><span class="identifier">first</span></code> hardcoded as the key part and <code class="computeroutput"><span class="identifier">pair</span><span class="special">.</span><span class="identifier">second</span></code> 39 hardcoded as the <code class="computeroutput"><span class="identifier">mapped_type</span></code>, 40 which is limiting and also not very useful in practice. Any intrusive associative 41 container can be used like a map using <a class="link" href="advanced_lookups_insertions.html" title="Advanced lookup and insertion functions for associative containers">advanced 42 lookup and insertions</a> and the user can change the key type in each lookup/insertion 43 check call. 44 </p> 45<p> 46 On the other hand, in many cases containers are indexed by a well-known key 47 type, and the user is forced to write some repetitive code using advanced lookup 48 and insertions. <span class="bold"><strong>Boost.Intrusive</strong></span> associative 49 containers offer an alternative to build a useful map-like lookup interfaces 50 without forcing users to define <code class="computeroutput"><span class="identifier">value_type</span></code>s 51 containing <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span></code>-like classes. The option is called 52 <code class="computeroutput"><a class="link" href="../boost/intrusive/key_of_value.html" title="Struct template key_of_value">boost::intrusive::key_of_value</a></code>. 53 </p> 54<p> 55 If a user specifies that option when defining a <code class="computeroutput"><span class="identifier">set</span><span class="special">/</span><span class="identifier">multiset</span></code> 56 intrusive container, it specifies a function object that will tell the container 57 which is the type of the <span class="emphasis"><em>key</em></span> that <code class="computeroutput"><span class="identifier">value_type</span></code> 58 holds and how to obtain it. This function object must be: 59 </p> 60<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 61<li class="listitem"> 62 Lightweight to copy. 63 </li> 64<li class="listitem"> 65 Default constructible (when the container constructor overload requires 66 it). 67 </li> 68<li class="listitem"> 69 It shall define: 70 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "> 71<li class="listitem"> 72 A <code class="computeroutput"><span class="identifier">type</span></code> member that 73 defines the type of the key 74 </li> 75<li class="listitem"> 76 A member function that returns the key derived a <code class="computeroutput"><span class="identifier">value_type</span></code>, 77 either by value or by const-reference. 78 </li> 79</ul></div> 80 </li> 81</ul></div> 82<p> 83 Let's see an example of how a set can be configured as a map indexed by an 84 integer stored in the <code class="computeroutput"><span class="identifier">value_type</span></code>: 85 </p> 86<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="keyword">static_assert</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 87<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">is_same</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 88<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">intrusive</span><span class="special">/</span><span class="identifier">set</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 89<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">intrusive</span><span class="special">/</span><span class="identifier">unordered_set</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 90<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">vector</span><span class="special">></span> 91<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 92 93<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">intrusive</span><span class="special">;</span> 94 95<span class="keyword">class</span> <span class="identifier">MyClass</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">set_base_hook</span><span class="special"><></span> 96 <span class="special">,</span> <span class="keyword">public</span> <span class="identifier">unordered_set_base_hook</span><span class="special"><></span> 97<span class="special">{</span> 98 <span class="keyword">public</span><span class="special">:</span> 99 <span class="keyword">int</span> <span class="identifier">first</span><span class="special">;</span> 100 <span class="keyword">explicit</span> <span class="identifier">MyClass</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">first</span><span class="special">(</span><span class="identifier">i</span><span class="special">){}</span> 101<span class="special">};</span> 102 103<span class="comment">//key_of_value function object, must:</span> 104<span class="comment">//- be default constructible if the container constructor requires it</span> 105<span class="comment">//- define the key type using "type"</span> 106<span class="comment">//- define an operator() taking "const value_type&" and</span> 107<span class="comment">// returning "type" or "const type &"</span> 108<span class="keyword">struct</span> <span class="identifier">first_int_is_key</span> 109<span class="special">{</span> 110 <span class="keyword">typedef</span> <span class="keyword">int</span> <span class="identifier">type</span><span class="special">;</span> 111 112 <span class="keyword">const</span> <span class="identifier">type</span> <span class="special">&</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">MyClass</span><span class="special">&</span> <span class="identifier">v</span><span class="special">)</span> <span class="keyword">const</span> 113 <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">first</span><span class="special">;</span> <span class="special">}</span> 114<span class="special">};</span> 115 116<span class="comment">//Define omap like ordered and unordered classes </span> 117<span class="keyword">typedef</span> <span class="identifier">set</span><span class="special"><</span> <span class="identifier">MyClass</span><span class="special">,</span> <span class="identifier">key_of_value</span><span class="special"><</span><span class="identifier">first_int_is_key</span><span class="special">></span> <span class="special">></span> <span class="identifier">OrderedMap</span><span class="special">;</span> 118<span class="keyword">typedef</span> <span class="identifier">unordered_set</span><span class="special"><</span> <span class="identifier">MyClass</span><span class="special">,</span> <span class="identifier">key_of_value</span><span class="special"><</span><span class="identifier">first_int_is_key</span><span class="special">></span> <span class="special">></span> <span class="identifier">UnorderedMap</span><span class="special">;</span> 119 120<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 121<span class="special">{</span> 122 <span class="identifier">BOOST_STATIC_ASSERT</span><span class="special">((</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_same</span><span class="special"><</span> <span class="identifier">OrderedMap</span><span class="special">::</span><span class="identifier">key_type</span><span class="special">,</span> <span class="keyword">int</span><span class="special">>::</span><span class="identifier">value</span><span class="special">));</span> 123 <span class="identifier">BOOST_STATIC_ASSERT</span><span class="special">((</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_same</span><span class="special"><</span><span class="identifier">UnorderedMap</span><span class="special">::</span><span class="identifier">key_type</span><span class="special">,</span> <span class="keyword">int</span><span class="special">>::</span><span class="identifier">value</span><span class="special">));</span> 124 125 <span class="comment">//Create several MyClass objects, each one with a different value</span> 126 <span class="comment">//and insert them into the omap</span> 127 <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span> <span class="identifier">values</span><span class="special">;</span> 128 <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">100</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">values</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">MyClass</span><span class="special">(</span><span class="identifier">i</span><span class="special">));</span> 129 130 <span class="comment">//Create ordered/unordered maps and insert values</span> 131 <span class="identifier">OrderedMap</span> <span class="identifier">omap</span><span class="special">(</span><span class="identifier">values</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">values</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span> 132 <span class="identifier">UnorderedMap</span><span class="special">::</span><span class="identifier">bucket_type</span> <span class="identifier">buckets</span><span class="special">[</span><span class="number">100</span><span class="special">];</span> 133 <span class="identifier">UnorderedMap</span> <span class="identifier">umap</span><span class="special">(</span><span class="identifier">values</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">values</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">UnorderedMap</span><span class="special">::</span><span class="identifier">bucket_traits</span><span class="special">(</span><span class="identifier">buckets</span><span class="special">,</span> <span class="number">100</span><span class="special">));</span> 134 135 <span class="comment">//Test each element using the key_type (int)</span> 136 <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">!=</span> <span class="number">100</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span> 137 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">omap</span><span class="special">.</span><span class="identifier">find</span><span class="special">(</span><span class="identifier">i</span><span class="special">)</span> <span class="special">!=</span> <span class="identifier">omap</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span> 138 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">umap</span><span class="special">.</span><span class="identifier">find</span><span class="special">(</span><span class="identifier">i</span><span class="special">)</span> <span class="special">!=</span> <span class="identifier">umap</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span> 139 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">omap</span><span class="special">.</span><span class="identifier">lower_bound</span><span class="special">(</span><span class="identifier">i</span><span class="special">)</span> <span class="special">!=</span> <span class="identifier">omap</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span> 140 <span class="identifier">assert</span><span class="special">(++</span><span class="identifier">omap</span><span class="special">.</span><span class="identifier">lower_bound</span><span class="special">(</span><span class="identifier">i</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">omap</span><span class="special">.</span><span class="identifier">upper_bound</span><span class="special">(</span><span class="identifier">i</span><span class="special">));</span> 141 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">omap</span><span class="special">.</span><span class="identifier">equal_range</span><span class="special">(</span><span class="identifier">i</span><span class="special">).</span><span class="identifier">first</span> <span class="special">!=</span> <span class="identifier">omap</span><span class="special">.</span><span class="identifier">equal_range</span><span class="special">(</span><span class="identifier">i</span><span class="special">).</span><span class="identifier">second</span><span class="special">);</span> 142 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">umap</span><span class="special">.</span><span class="identifier">equal_range</span><span class="special">(</span><span class="identifier">i</span><span class="special">).</span><span class="identifier">first</span> <span class="special">!=</span> <span class="identifier">umap</span><span class="special">.</span><span class="identifier">equal_range</span><span class="special">(</span><span class="identifier">i</span><span class="special">).</span><span class="identifier">second</span><span class="special">);</span> 143 <span class="special">}</span> 144 145 <span class="comment">//Count and erase by key</span> 146 <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">!=</span> <span class="number">100</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span> 147 <span class="identifier">assert</span><span class="special">(</span><span class="number">1</span> <span class="special">==</span> <span class="identifier">omap</span><span class="special">.</span><span class="identifier">count</span><span class="special">(</span><span class="identifier">i</span><span class="special">));</span> 148 <span class="identifier">assert</span><span class="special">(</span><span class="number">1</span> <span class="special">==</span> <span class="identifier">umap</span><span class="special">.</span><span class="identifier">count</span><span class="special">(</span><span class="identifier">i</span><span class="special">));</span> 149 <span class="identifier">assert</span><span class="special">(</span><span class="number">1</span> <span class="special">==</span> <span class="identifier">omap</span><span class="special">.</span><span class="identifier">erase</span><span class="special">(</span><span class="identifier">i</span><span class="special">));</span> 150 <span class="identifier">assert</span><span class="special">(</span><span class="number">1</span> <span class="special">==</span> <span class="identifier">umap</span><span class="special">.</span><span class="identifier">erase</span><span class="special">(</span><span class="identifier">i</span><span class="special">));</span> 151 <span class="special">}</span> 152 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">omap</span><span class="special">.</span><span class="identifier">empty</span><span class="special">());</span> 153 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">umap</span><span class="special">.</span><span class="identifier">empty</span><span class="special">());</span> 154 155 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 156<span class="special">}</span> 157</pre> 158</div> 159<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 160<td align="left"></td> 161<td align="right"><div class="copyright-footer">Copyright © 2005 Olaf Krzikalla<br>Copyright © 2006-2015 Ion Gaztanaga<p> 162 Distributed under the Boost Software License, Version 1.0. (See accompanying 163 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>) 164 </p> 165</div></td> 166</tr></table> 167<hr> 168<div class="spirit-nav"> 169<a accesskey="p" href="unordered_set_unordered_multiset.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../intrusive.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="avl_set_multiset.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 170</div> 171</body> 172</html> 173
