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1<?xml version="1.0" encoding="utf-8" ?>
2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
3<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
4<head>
5<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
6<meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" />
7<title>Bidirectional Traversal Concept</title>
8<link rel="stylesheet" href="../../../rst.css" type="text/css" />
9</head>
10<body>
11<div class="document" id="bidirectional-traversal-concept">
12<h1 class="title">Bidirectional Traversal Concept</h1>
13
14<!-- Copyright David Abrahams 2006. Distributed under the Boost -->
15<!-- Software License, Version 1.0. (See accompanying -->
16<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
17<p>A class or built-in type <tt class="docutils literal"><span class="pre">X</span></tt> models the <em>Bidirectional Traversal</em>
18concept if, in addition to <tt class="docutils literal"><span class="pre">X</span></tt> meeting the requirements of Forward
19Traversal Iterator, the following expressions are valid and respect
20the stated semantics.</p>
21<table border="1" class="docutils">
22<colgroup>
23<col width="38%" />
24<col width="37%" />
25<col width="25%" />
26</colgroup>
27<thead valign="bottom">
28<tr><th class="head" colspan="3">Bidirectional Traversal Iterator Requirements (in addition to Forward Traversal
29Iterator)</th>
30</tr>
31<tr><th class="head">Expression</th>
32<th class="head">Return Type</th>
33<th class="head">Assertion/Semantics /
34Pre-/Post-condition</th>
35</tr>
36</thead>
37<tbody valign="top">
38<tr><td><tt class="docutils literal"><span class="pre">--r</span></tt></td>
39<td><tt class="docutils literal"><span class="pre">X&amp;</span></tt></td>
40<td>pre: there exists
41<tt class="docutils literal"><span class="pre">s</span></tt> such that <tt class="docutils literal"><span class="pre">r</span>
42<span class="pre">==</span> <span class="pre">++s</span></tt>.  post:
43<tt class="docutils literal"><span class="pre">s</span></tt> is
44dereferenceable.
45<tt class="docutils literal"><span class="pre">--(++r)</span> <span class="pre">==</span> <span class="pre">r</span></tt>.
46<tt class="docutils literal"><span class="pre">--r</span> <span class="pre">==</span> <span class="pre">--s</span></tt>
47implies <tt class="docutils literal"><span class="pre">r</span> <span class="pre">==</span>
48<span class="pre">s</span></tt>. <tt class="docutils literal"><span class="pre">&amp;r</span> <span class="pre">==</span> <span class="pre">&amp;--r</span></tt>.</td>
49</tr>
50<tr><td><tt class="docutils literal"><span class="pre">r--</span></tt></td>
51<td>convertible to <tt class="docutils literal"><span class="pre">const</span> <span class="pre">X&amp;</span></tt></td>
52<td><pre class="first last literal-block">
53{
54  X tmp = r;
55  --r;
56  return tmp;
57}
58</pre>
59</td>
60</tr>
61<tr><td><tt class="docutils literal"><span class="pre">iterator_traversal&lt;X&gt;::type</span></tt></td>
62<td>Convertible to
63<tt class="docutils literal"><span class="pre">bidirectional_traversal_tag</span></tt></td>
64<td>&nbsp;</td>
65</tr>
66</tbody>
67</table>
68</div>
69<div class="footer">
70<hr class="footer" />
71<a class="reference external" href="BidirectionalTraversal.rst">View document source</a>.
72Generated by <a class="reference external" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference external" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.
73
74</div>
75</body>
76</html>
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