<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" /> <title>Bidirectional Traversal Concept</title> <link rel="stylesheet" href="../../../rst.css" type="text/css" /> </head> <body> <div class="document" id="bidirectional-traversal-concept"> <h1 class="title">Bidirectional Traversal Concept</h1> <!-- Copyright David Abrahams 2006. Distributed under the Boost --> <!-- Software License, Version 1.0. (See accompanying --> <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) --> <p>A class or built-in type <tt class="docutils literal"><span class="pre">X</span></tt> models the <em>Bidirectional Traversal</em> concept if, in addition to <tt class="docutils literal"><span class="pre">X</span></tt> meeting the requirements of Forward Traversal Iterator, the following expressions are valid and respect the stated semantics.</p> <table border="1" class="docutils"> <colgroup> <col width="38%" /> <col width="37%" /> <col width="25%" /> </colgroup> <thead valign="bottom"> <tr><th class="head" colspan="3">Bidirectional Traversal Iterator Requirements (in addition to Forward Traversal Iterator)</th> </tr> <tr><th class="head">Expression</th> <th class="head">Return Type</th> <th class="head">Assertion/Semantics / Pre-/Post-condition</th> </tr> </thead> <tbody valign="top"> <tr><td><tt class="docutils literal"><span class="pre">--r</span></tt></td> <td><tt class="docutils literal"><span class="pre">X&</span></tt></td> <td>pre: there exists <tt class="docutils literal"><span class="pre">s</span></tt> such that <tt class="docutils literal"><span class="pre">r</span> <span class="pre">==</span> <span class="pre">++s</span></tt>. post: <tt class="docutils literal"><span class="pre">s</span></tt> is dereferenceable. <tt class="docutils literal"><span class="pre">--(++r)</span> <span class="pre">==</span> <span class="pre">r</span></tt>. <tt class="docutils literal"><span class="pre">--r</span> <span class="pre">==</span> <span class="pre">--s</span></tt> implies <tt class="docutils literal"><span class="pre">r</span> <span class="pre">==</span> <span class="pre">s</span></tt>. <tt class="docutils literal"><span class="pre">&r</span> <span class="pre">==</span> <span class="pre">&--r</span></tt>.</td> </tr> <tr><td><tt class="docutils literal"><span class="pre">r--</span></tt></td> <td>convertible to <tt class="docutils literal"><span class="pre">const</span> <span class="pre">X&</span></tt></td> <td><pre class="first last literal-block"> { X tmp = r; --r; return tmp; } </pre> </td> </tr> <tr><td><tt class="docutils literal"><span class="pre">iterator_traversal<X>::type</span></tt></td> <td>Convertible to <tt class="docutils literal"><span class="pre">bidirectional_traversal_tag</span></tt></td> <td> </td> </tr> </tbody> </table> </div> <div class="footer"> <hr class="footer" /> <a class="reference external" href="BidirectionalTraversal.rst">View document source</a>. Generated 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. </div> </body> </html>