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>Obtaining iterators from values</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="using_smart_pointers.html" title="Using smart pointers with Boost.Intrusive containers"> 11<link rel="next" href="any_hooks.html" title="Any Hooks: A single hook for any Intrusive container"> 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="using_smart_pointers.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="any_hooks.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.obtaining_iterators_from_values"></a><a class="link" href="obtaining_iterators_from_values.html" title="Obtaining iterators from values">Obtaining iterators 29 from values</a> 30</h2></div></div></div> 31<p> 32 <span class="bold"><strong>Boost.Intrusive</strong></span> offers another useful feature 33 that's not present in STL containers: it's possible to obtain an iterator to 34 a value from the value itself. This feature is implemented in <span class="bold"><strong>Boost.Intrusive</strong></span> 35 containers by a function called <code class="computeroutput"><span class="identifier">iterator_to</span></code>: 36 </p> 37<pre class="programlisting"><span class="identifier">iterator</span> <span class="identifier">iterator_to</span><span class="special">(</span><span class="identifier">reference</span> <span class="identifier">value</span><span class="special">);</span> 38<span class="identifier">const_iterator</span> <span class="identifier">iterator_to</span><span class="special">(</span><span class="identifier">const_reference</span> <span class="identifier">value</span><span class="special">);</span> 39</pre> 40<p> 41 For <span class="bold"><strong>Boost.Intrusive</strong></span> containers that have local 42 iterators, like unordered associative containers, we can also obtain local 43 iterators: 44 </p> 45<pre class="programlisting"><span class="identifier">local_iterator</span> <span class="identifier">local_iterator_to</span><span class="special">(</span><span class="identifier">reference</span> <span class="identifier">value</span><span class="special">);</span> 46<span class="identifier">const_local_iterator</span> <span class="identifier">local_iterator_to</span><span class="special">(</span><span class="identifier">const_reference</span> <span class="identifier">value</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> 47</pre> 48<p> 49 For most <span class="bold"><strong>Boost.Intrusive</strong></span> containers (<code class="computeroutput"><a class="link" href="../boost/intrusive/list.html" title="Class template list">list</a></code>, <code class="computeroutput"><a class="link" href="../boost/intrusive/slist.html" title="Class template slist">slist</a></code>, 50 <code class="computeroutput"><a class="link" href="../boost/intrusive/set.html" title="Class template set">set</a></code>, <code class="computeroutput"><a class="link" href="../boost/intrusive/multiset.html" title="Class template multiset">multiset</a></code>) 51 we have an alternative static <code class="computeroutput"><span class="identifier">s_iterator_to</span></code> 52 function. 53 </p> 54<p> 55 For unordered associative containers (<code class="computeroutput"><a class="link" href="../boost/intrusive/unordered_set.html" title="Class template unordered_set">unordered_set</a></code>, 56 <code class="computeroutput"><a class="link" href="../boost/intrusive/multiset.html" title="Class template multiset">multiset</a></code>), <code class="computeroutput"><span class="identifier">iterator_to</span></code> has no static alternative function. 57 On the other hand, <code class="computeroutput"><span class="identifier">local_iterator_to</span></code> 58 functions have their <code class="computeroutput"><span class="identifier">s_local_iterator_to</span></code> 59 static alternatives. 60 </p> 61<p> 62 Alternative static functions are available under certain circumstances explained 63 in the <a class="link" href="value_traits.html#intrusive.value_traits.stateful_value_traits" title="Stateful value traits">Stateful 64 value traits</a> section; if the programmer uses hooks provided by <span class="bold"><strong>Boost.Intrusive</strong></span>, those functions will be available. 65 </p> 66<p> 67 Let's see a small function that shows the use of <code class="computeroutput"><span class="identifier">iterator_to</span></code> 68 and <code class="computeroutput"><span class="identifier">local_iterator_to</span></code>: 69 </p> 70<pre class="programlisting"><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">list</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 71<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> 72<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">functional</span><span class="special">/</span><span class="identifier">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 73<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">vector</span><span class="special">></span> 74 75<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> 76 77<span class="keyword">class</span> <span class="identifier">intrusive_data</span> 78<span class="special">{</span> 79 <span class="keyword">int</span> <span class="identifier">data_id_</span><span class="special">;</span> 80 <span class="keyword">public</span><span class="special">:</span> 81 82 <span class="keyword">void</span> <span class="identifier">set</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">id</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">data_id_</span> <span class="special">=</span> <span class="identifier">id</span><span class="special">;</span> <span class="special">}</span> 83 84 <span class="comment">//This class can be inserted in an intrusive list</span> 85 <span class="identifier">list_member_hook</span><span class="special"><></span> <span class="identifier">list_hook_</span><span class="special">;</span> 86 87 <span class="comment">//This class can be inserted in an intrusive unordered_set</span> 88 <span class="identifier">unordered_set_member_hook</span><span class="special"><></span> <span class="identifier">unordered_set_hook_</span><span class="special">;</span> 89 90 <span class="comment">//Comparison operators</span> 91 <span class="keyword">friend</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">==(</span><span class="keyword">const</span> <span class="identifier">intrusive_data</span> <span class="special">&</span><span class="identifier">a</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">intrusive_data</span> <span class="special">&</span><span class="identifier">b</span><span class="special">)</span> 92 <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">data_id_</span> <span class="special">==</span> <span class="identifier">b</span><span class="special">.</span><span class="identifier">data_id_</span><span class="special">;</span> <span class="special">}</span> 93 94 <span class="keyword">friend</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!=(</span><span class="keyword">const</span> <span class="identifier">intrusive_data</span> <span class="special">&</span><span class="identifier">a</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">intrusive_data</span> <span class="special">&</span><span class="identifier">b</span><span class="special">)</span> 95 <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">data_id_</span> <span class="special">!=</span> <span class="identifier">b</span><span class="special">.</span><span class="identifier">data_id_</span><span class="special">;</span> <span class="special">}</span> 96 97 <span class="comment">//The hash function</span> 98 <span class="keyword">friend</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">hash_value</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">intrusive_data</span> <span class="special">&</span><span class="identifier">i</span><span class="special">)</span> 99 <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">hash</span><span class="special"><</span><span class="keyword">int</span><span class="special">>()(</span><span class="identifier">i</span><span class="special">.</span><span class="identifier">data_id_</span><span class="special">);</span> <span class="special">}</span> 100<span class="special">};</span> 101 102<span class="comment">//Definition of the intrusive list that will hold intrusive_data</span> 103<span class="keyword">typedef</span> <span class="identifier">member_hook</span><span class="special"><</span><span class="identifier">intrusive_data</span><span class="special">,</span> <span class="identifier">list_member_hook</span><span class="special"><></span> 104 <span class="special">,</span> <span class="special">&</span><span class="identifier">intrusive_data</span><span class="special">::</span><span class="identifier">list_hook_</span><span class="special">></span> <span class="identifier">MemberListOption</span><span class="special">;</span> 105<span class="keyword">typedef</span> <span class="identifier">list</span><span class="special"><</span><span class="identifier">intrusive_data</span><span class="special">,</span> <span class="identifier">MemberListOption</span><span class="special">></span> <span class="identifier">list_t</span><span class="special">;</span> 106 107<span class="comment">//Definition of the intrusive unordered_set that will hold intrusive_data</span> 108<span class="keyword">typedef</span> <span class="identifier">member_hook</span> 109 <span class="special"><</span> <span class="identifier">intrusive_data</span><span class="special">,</span> <span class="identifier">unordered_set_member_hook</span><span class="special"><></span> 110 <span class="special">,</span> <span class="special">&</span><span class="identifier">intrusive_data</span><span class="special">::</span><span class="identifier">unordered_set_hook_</span><span class="special">></span> <span class="identifier">MemberUsetOption</span><span class="special">;</span> 111<span class="keyword">typedef</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> 112 <span class="special"><</span> <span class="identifier">intrusive_data</span><span class="special">,</span> <span class="identifier">MemberUsetOption</span><span class="special">></span> <span class="identifier">unordered_set_t</span><span class="special">;</span> 113 114<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 115<span class="special">{</span> 116 <span class="comment">//Create MaxElem objects</span> 117 <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">MaxElem</span> <span class="special">=</span> <span class="number">100</span><span class="special">;</span> 118 <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">intrusive_data</span><span class="special">></span> <span class="identifier">nodes</span><span class="special">(</span><span class="identifier">MaxElem</span><span class="special">);</span> 119 120 <span class="comment">//Declare the intrusive containers</span> 121 <span class="identifier">list_t</span> <span class="identifier">list</span><span class="special">;</span> 122 <span class="identifier">unordered_set_t</span><span class="special">::</span><span class="identifier">bucket_type</span> <span class="identifier">buckets</span><span class="special">[</span><span class="identifier">MaxElem</span><span class="special">];</span> 123 <span class="identifier">unordered_set_t</span> <span class="identifier">unordered_set</span> 124 <span class="special">(</span><span class="identifier">unordered_set_t</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="identifier">MaxElem</span><span class="special">));</span> 125 126 <span class="comment">//Initialize all the nodes</span> 127 <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="identifier">MaxElem</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">nodes</span><span class="special">[</span><span class="identifier">i</span><span class="special">].</span><span class="identifier">set</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span> 128 129 <span class="comment">//Now insert them in both intrusive containers</span> 130 <span class="identifier">list</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">nodes</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">nodes</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span> 131 <span class="identifier">unordered_set</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">nodes</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">nodes</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span> 132 133 <span class="comment">//Now check the iterator_to function</span> 134 <span class="identifier">list_t</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">list_it</span><span class="special">(</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">begin</span><span class="special">());</span> 135 <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="identifier">MaxElem</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">,</span> <span class="special">++</span><span class="identifier">list_it</span><span class="special">)</span> 136 <span class="keyword">if</span><span class="special">(</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">iterator_to</span><span class="special">(</span><span class="identifier">nodes</span><span class="special">[</span><span class="identifier">i</span><span class="special">])</span> <span class="special">!=</span> <span class="identifier">list_it</span> <span class="special">||</span> 137 <span class="identifier">list_t</span><span class="special">::</span><span class="identifier">s_iterator_to</span><span class="special">(</span><span class="identifier">nodes</span><span class="special">[</span><span class="identifier">i</span><span class="special">])</span> <span class="special">!=</span> <span class="identifier">list_it</span><span class="special">)</span> 138 <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> 139 140 <span class="comment">//Now check unordered_set::s_iterator_to (which is a member function)</span> 141 <span class="comment">//and unordered_set::s_local_iterator_to (which is an static member function)</span> 142 <span class="identifier">unordered_set_t</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">unordered_set_it</span><span class="special">(</span><span class="identifier">unordered_set</span><span class="special">.</span><span class="identifier">begin</span><span class="special">());</span> 143 <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="identifier">MaxElem</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span> 144 <span class="identifier">unordered_set_it</span> <span class="special">=</span> <span class="identifier">unordered_set</span><span class="special">.</span><span class="identifier">find</span><span class="special">(</span><span class="identifier">nodes</span><span class="special">[</span><span class="identifier">i</span><span class="special">]);</span> 145 <span class="keyword">if</span><span class="special">(</span><span class="identifier">unordered_set</span><span class="special">.</span><span class="identifier">iterator_to</span><span class="special">(</span><span class="identifier">nodes</span><span class="special">[</span><span class="identifier">i</span><span class="special">])</span> <span class="special">!=</span> <span class="identifier">unordered_set_it</span><span class="special">)</span> 146 <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> 147 <span class="keyword">if</span><span class="special">(*</span><span class="identifier">unordered_set</span><span class="special">.</span><span class="identifier">local_iterator_to</span><span class="special">(</span><span class="identifier">nodes</span><span class="special">[</span><span class="identifier">i</span><span class="special">])</span> <span class="special">!=</span> <span class="special">*</span><span class="identifier">unordered_set_it</span> <span class="special">||</span> 148 <span class="special">*</span><span class="identifier">unordered_set_t</span><span class="special">::</span><span class="identifier">s_local_iterator_to</span><span class="special">(</span><span class="identifier">nodes</span><span class="special">[</span><span class="identifier">i</span><span class="special">])</span> <span class="special">!=</span> <span class="special">*</span><span class="identifier">unordered_set_it</span> <span class="special">)</span> 149 <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> 150 <span class="special">}</span> 151 152 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 153<span class="special">}</span> 154</pre> 155</div> 156<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 157<td align="left"></td> 158<td align="right"><div class="copyright-footer">Copyright © 2005 Olaf Krzikalla<br>Copyright © 2006-2015 Ion Gaztanaga<p> 159 Distributed under the Boost Software License, Version 1.0. (See accompanying 160 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>) 161 </p> 162</div></td> 163</tr></table> 164<hr> 165<div class="spirit-nav"> 166<a accesskey="p" href="using_smart_pointers.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="any_hooks.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 167</div> 168</body> 169</html> 170
