1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Obtaining iterators from values</title>
<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.76.1">
<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset">
<link rel="up" href="../intrusive.html" title="Chapter 16. Boost.Intrusive">
<link rel="prev" href="using_smart_pointers.html" title="Using smart pointers with Boost.Intrusive containers">
<link rel="next" href="any_hooks.html" title="Any Hooks: A single hook for any Intrusive container">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td>
<td align="center"><a href="../../../index.html">Home</a></td>
<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<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>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="intrusive.obtaining_iterators_from_values"></a><a class="link" href="obtaining_iterators_from_values.html" title="Obtaining iterators from values">Obtaining iterators
from values</a>
</h2></div></div></div>
<p>
<span class="bold"><strong>Boost.Intrusive</strong></span> offers another useful feature
that's not present in STL containers: it's possible to obtain an iterator to
a value from the value itself. This feature is implemented in <span class="bold"><strong>Boost.Intrusive</strong></span>
containers by a function called <code class="computeroutput"><span class="identifier">iterator_to</span></code>:
</p>
<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>
<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>
</pre>
<p>
For <span class="bold"><strong>Boost.Intrusive</strong></span> containers that have local
iterators, like unordered associative containers, we can also obtain local
iterators:
</p>
<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>
<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>
</pre>
<p>
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>,
<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>)
we have an alternative static <code class="computeroutput"><span class="identifier">s_iterator_to</span></code>
function.
</p>
<p>
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>,
<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.
On the other hand, <code class="computeroutput"><span class="identifier">local_iterator_to</span></code>
functions have their <code class="computeroutput"><span class="identifier">s_local_iterator_to</span></code>
static alternatives.
</p>
<p>
Alternative static functions are available under certain circumstances explained
in the <a class="link" href="value_traits.html#intrusive.value_traits.stateful_value_traits" title="Stateful value traits">Stateful
value traits</a> section; if the programmer uses hooks provided by <span class="bold"><strong>Boost.Intrusive</strong></span>, those functions will be available.
</p>
<p>
Let's see a small function that shows the use of <code class="computeroutput"><span class="identifier">iterator_to</span></code>
and <code class="computeroutput"><span class="identifier">local_iterator_to</span></code>:
</p>
<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>
<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>
<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>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">vector</span><span class="special">></span>
<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>
<span class="keyword">class</span> <span class="identifier">intrusive_data</span>
<span class="special">{</span>
<span class="keyword">int</span> <span class="identifier">data_id_</span><span class="special">;</span>
<span class="keyword">public</span><span class="special">:</span>
<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>
<span class="comment">//This class can be inserted in an intrusive list</span>
<span class="identifier">list_member_hook</span><span class="special"><></span> <span class="identifier">list_hook_</span><span class="special">;</span>
<span class="comment">//This class can be inserted in an intrusive unordered_set</span>
<span class="identifier">unordered_set_member_hook</span><span class="special"><></span> <span class="identifier">unordered_set_hook_</span><span class="special">;</span>
<span class="comment">//Comparison operators</span>
<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>
<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>
<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>
<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>
<span class="comment">//The hash function</span>
<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>
<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>
<span class="special">};</span>
<span class="comment">//Definition of the intrusive list that will hold intrusive_data</span>
<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>
<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>
<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>
<span class="comment">//Definition of the intrusive unordered_set that will hold intrusive_data</span>
<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">unordered_set_member_hook</span><span class="special"><></span>
<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>
<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>
<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>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="comment">//Create MaxElem objects</span>
<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>
<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>
<span class="comment">//Declare the intrusive containers</span>
<span class="identifier">list_t</span> <span class="identifier">list</span><span class="special">;</span>
<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>
<span class="identifier">unordered_set_t</span> <span class="identifier">unordered_set</span>
<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>
<span class="comment">//Initialize all the nodes</span>
<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>
<span class="comment">//Now insert them in both intrusive containers</span>
<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>
<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>
<span class="comment">//Now check the iterator_to function</span>
<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>
<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>
<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>
<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>
<span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>
<span class="comment">//Now check unordered_set::s_iterator_to (which is a member function)</span>
<span class="comment">//and unordered_set::s_local_iterator_to (which is an static member function)</span>
<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>
<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">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>
<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>
<span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>
<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>
<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>
<span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>
<span class="special">}</span>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2005 Olaf Krzikalla<br>Copyright © 2006-2015 Ion Gaztanaga<p>
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>)
</p>
</div></td>
</tr></table>
<hr>
<div class="spirit-nav">
<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>
</div>
</body>
</html>
|
