<?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 0.7: http://docutils.sourceforge.net/" /> <title>The MPL Reference Manual: Bidirectional Iterator</title> <link rel="stylesheet" href="../style.css" type="text/css" /> </head> <body class="docframe refmanual"> <table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./forward-iterator.html" class="navigation-link">Prev</a> <a href="./random-access-iterator.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./forward-iterator.html" class="navigation-link">Back</a> <a href="./random-access-iterator.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./iterators-concepts.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> <td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./iterators.html" class="navigation-link">Iterators</a> / <a href="./iterators-concepts.html" class="navigation-link">Concepts</a> / <a href="./bidirectional-iterator.html" class="navigation-link">Bidirectional Iterator</a></td> </tr></table><div class="header-separator"></div> <div class="section" id="bidirectional-iterator"> <h1><a class="toc-backref" href="./iterators-concepts.html#id1451">Bidirectional Iterator</a></h1> <div class="section" id="id390"> <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> <p>A <a class="reference internal" href="./bidirectional-iterator.html">Bidirectional Iterator</a> is a <a class="reference internal" href="./forward-iterator.html">Forward Iterator</a> that provides a way to obtain an iterator to the previous element in a sequence.</p> </div> <div class="section" id="id391"> <h3><a class="subsection-title" href="#refinement-of" name="refinement-of">Refinement of</a></h3> <p><a class="reference internal" href="./forward-iterator.html">Forward Iterator</a></p> </div> <div class="section" id="id392"> <h3><a class="subsection-title" href="#definitions" name="definitions">Definitions</a></h3> <ul class="simple"> <li>a bidirectional iterator <tt class="literal"><span class="pre">i</span></tt> is <cite>decrementable</cite> if there is a "previous" iterator, that is, if <tt class="literal"><span class="pre"><a href="./prior.html" class="identifier">prior</a><i>::type</span></tt> expression is well-defined; iterators pointing to the first element of the sequence are not decrementable.</li> </ul> </div> <div class="section" id="id393"> <h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3> <p>In addition to the requirements defined in <a class="reference internal" href="./forward-iterator.html">Forward Iterator</a>, the following requirements must be met.</p> <table border="1" class="docutils table"> <colgroup> <col width="25%" /> <col width="46%" /> <col width="29%" /> </colgroup> <thead valign="bottom"> <tr><th class="head">Expression</th> <th class="head">Type</th> <th class="head">Complexity</th> </tr> </thead> <tbody valign="top"> <tr><td><tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a><i>::type</span></tt></td> <td><a class="reference internal" href="./bidirectional-iterator.html">Bidirectional Iterator</a></td> <td>Amortized constant time</td> </tr> <tr><td><tt class="literal"><span class="pre"><a href="./prior.html" class="identifier">prior</a><i>::type</span></tt></td> <td><a class="reference internal" href="./bidirectional-iterator.html">Bidirectional Iterator</a></td> <td>Amortized constant time</td> </tr> <tr><td><tt class="literal"><span class="pre">i::category</span></tt></td> <td><a class="reference internal" href="./integral-constant.html">Integral Constant</a>, convertible to <tt class="literal"><span class="pre">bidirectional_iterator_tag</span></tt></td> <td>Constant time</td> </tr> </tbody> </table> </div> <div class="section" id="id394"> <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> <pre class="literal-block"> typedef <a href="./prior.html" class="identifier">prior</a><i>::type j; </pre> <table class="docutils field-list" frame="void" rules="none"> <col class="field-name" /> <col class="field-body" /> <tbody valign="top"> <tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">i</span></tt> is decrementable</td> </tr> <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">j</span></tt> is an iterator pointing to the previous element of the sequence</td> </tr> <tr class="field"><th class="field-name">Postcondition:</th><td class="field-body"><tt class="literal"><span class="pre">j</span></tt> is dereferenceable and incrementable</td> </tr> </tbody> </table> </div> <div class="section" id="id395"> <h3><a class="subsection-title" href="#invariants" name="invariants">Invariants</a></h3> <p>For any bidirectional iterators <tt class="literal"><span class="pre">i</span></tt> and <tt class="literal"><span class="pre">j</span></tt> the following invariants always hold:</p> <ul class="simple"> <li>If <tt class="literal"><span class="pre">i</span></tt> is incrementable, then <tt class="literal"><span class="pre"><a href="./prior.html" class="identifier">prior</a><</span> <span class="pre"><a href="./next.html" class="identifier">next</a><i>::type</span> <span class="pre">>::type</span></tt> is a null operation; similarly, if <tt class="literal"><span class="pre">i</span></tt> is decrementable, <tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a><</span> <span class="pre"><a href="./prior.html" class="identifier">prior</a><i>::type</span> <span class="pre">>::type</span></tt> is a null operation.</li> </ul> </div> <div class="section" id="id396"> <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> <p><a class="reference internal" href="./iterators.html">Iterators</a>, <a class="reference internal" href="./forward-iterator.html">Forward Iterator</a>, <a class="reference internal" href="./random-access-iterator.html">Random Access Iterator</a>, <a class="reference internal" href="./bidirectional-sequence.html">Bidirectional Sequence</a>, <a class="reference internal" href="./prior.html">prior</a></p> <!-- Iterators/Concepts//Random Access Iterator |30 --> </div> </div> <div class="footer-separator"></div> <table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./forward-iterator.html" class="navigation-link">Prev</a> <a href="./random-access-iterator.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./forward-iterator.html" class="navigation-link">Back</a> <a href="./random-access-iterator.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./iterators-concepts.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> <td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body> </html>