<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Concept BidirectionalIterator</title> <link rel="stylesheet" href="boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> <link rel="up" href="id313989-bb.html#concepts.reference" title="Concept reference"> <link rel="prev" href="ForwardIterator.html" title="Concept ForwardIterator"> <link rel="next" href="RandomAccessIterator.html" title="Concept RandomAccessIterator"> </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="ForwardIterator.html"><img src="../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="id313989-bb.html#concepts.reference"><img src="../../doc/html/images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="../../doc/html/images/home.png" alt="Home"></a><a accesskey="n" href="RandomAccessIterator.html"><img src="../../doc/html/images/next.png" alt="Next"></a> </div> <div class="refentry" title="Concept BidirectionalIterator"> <a name="BidirectionalIterator"></a><div class="titlepage"></div> <div class="refnamediv"> <h2><span class="refentrytitle">Concept BidirectionalIterator</span></h2> <p>BidirectionalIterator</p> </div> <div class="refsect1" title="Description"> <a name="id730234"></a><h2>Description</h2> <p>A bidirectional iterator is an iterator that can read through a sequence of values. It can move in either direction through the sequence, and can be either mutable (data pointed to by it can be changed) or not mutable.</p> <p>An iterator represents a position in a sequence. Therefore, the iterator can point into the sequence (returning a value when dereferenced and being incrementable), or be off-the-end (and not dereferenceable or incrementable).</p> </div> <div class="refsect1" title="Refinement of"> <a name="id730252"></a><h2>Refinement of</h2> <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="link" href="ForwardIterator.html" title="Concept ForwardIterator">ForwardIterator</a></p></li></ul></div> </div> <div class="refsect1" title="Associated types"> <a name="id730265"></a><h2>Associated types</h2> <div class="itemizedlist"><ul class="itemizedlist" type="disc"> <li class="listitem"> <p><span class="bold"><strong>value_type</strong></span></p> <pre class="literallayout">std::iterator_traits<Iter>::value_type</pre> <p>The value type of the iterator</p> </li> <li class="listitem"> <p><span class="bold"><strong>category</strong></span></p> <pre class="literallayout">std::iterator_traits<Iter>::iterator_category</pre> <p>The category of the iterator</p> </li> </ul></div> </div> <div class="refsect1" title="Notation"> <a name="id730305"></a><h2>Notation</h2> <div class="variablelist"><dl> <dt><span class="term">Iter</span></dt> <dd>A type playing the role of iterator-type in the <a class="link" href="BidirectionalIterator.html" title="Concept BidirectionalIterator">BidirectionalIterator</a> concept.</dd> <dt> <span class="term"><code class="varname">i</code>, </span><span class="term"><code class="varname">j</code></span> </dt> <dd>Objects of type Iter</dd> <dt><span class="term"><code class="varname">x</code></span></dt> <dd>Object of type value_type</dd> </dl></div> </div> <div class="refsect1" title="Type expressions"> <a name="id730343"></a><h2>Type expressions</h2> <div class="variablelist"><dl> <dt><span class="term">Category tag</span></dt> <dd><p><span class="type">category</span> must be derived from <span class="type">std::bidirectional_iterator_tag</span>. </p></dd> </dl></div> </div> <div class="refsect1" title="Valid expressions"> <a name="id730362"></a><h2>Valid expressions</h2> <div class="informaltable"><table class="table"> <colgroup> <col> <col> <col> <col> <col> <col> </colgroup> <thead><tr> <th>Name</th> <th>Expression</th> <th>Type</th> <th>Precondition</th> <th>Semantics</th> <th>Postcondition</th> </tr></thead> <tbody> <tr> <td><p>Predecrement</p></td> <td><p>--i</p></td> <td><p><span class="type">Iter &</span></p></td> <td><p><code class="computeroutput">i</code> is incrementable (not off-the-end) and some dereferenceable iterator <code class="computeroutput">j</code> exists such that <code class="computeroutput">i == ++j</code></p></td> <td> </td> <td> </td> </tr> <tr> <td><p>Postdecrement</p></td> <td><p>i--</p></td> <td><p><span class="type">Iter</span></p></td> <td><p>Same as for predecrement</p></td> <td><p>Equivalent to <code class="computeroutput">{Iter j = i; --i; return j;}</code></p></td> <td><p><code class="computeroutput">i</code> is dereferenceable or off-the-end</p></td> </tr> </tbody> </table></div> </div> <div class="refsect1" title="Complexity"> <a name="id730453"></a><h2>Complexity</h2> <p> All iterator operations must take amortized constant time. </p> </div> <div class="refsect1" title="Invariants"> <a name="id730460"></a><h2>Invariants</h2> <div class="variablelist"><dl> <dt><span class="term">Predecrement must return object</span></dt> <dd><p> <code class="computeroutput">&i = &(--i)</code> </p></dd> <dt><span class="term">Unique path through sequence</span></dt> <dd><p> <code class="computeroutput">i == j</code> implies <code class="computeroutput">--i == --j</code> </p></dd> <dt><span class="term">Increment and decrement are inverses</span></dt> <dd><p> <code class="computeroutput">++i; --i;</code> and <code class="computeroutput">--i; ++i;</code> must end up with the value of <code class="computeroutput">i</code> unmodified, if <code class="computeroutput">i</code> both of the operations in the pair are valid. </p></dd> </dl></div> </div> <div class="refsect1" title="Models"> <a name="id730528"></a><h2>Models</h2> <div class="itemizedlist"><ul class="itemizedlist" type="disc"> <li class="listitem"><span class="simplelist"><span class="type">T *</span></span></li> <li class="listitem"><span class="simplelist"><span class="type">std::list<T>::iterator</span></span></li> </ul></div> </div> <div class="refsect1" title="See also"> <a name="id730549"></a><h2>See also</h2> <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="link" href="RandomAccessIterator.html" title="Concept RandomAccessIterator">RandomAccessIterator</a></p></li></ul></div> </div> </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 © 2001, 2002 Indiana University<br>Copyright © 2000, 2001 University of Notre Dame du Lac<br>Copyright © 2000 Jeremy Siek, Lie-Quan Lee, Andrew Lumsdaine<br>Copyright © 1996-1999 Silicon Graphics Computer Systems, Inc.<br>Copyright © 1994 Hewlett-Packard Company<p>Distributed under the Boost Software License, Version 1.0. (See accompanying file <code class="filename">LICENSE_1_0.txt</code> 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> <p>This product includes software developed at the University of Notre Dame and the Pervasive Technology Labs at Indiana University. For technical information contact Andrew Lumsdaine at the Pervasive Technology Labs at Indiana University. For administrative and license questions contact the Advanced Research and Technology Institute at 351 West 10th Street. Indianapolis, Indiana 46202, phone 317-278-4100, fax 317-274-5902.</p> <p>Some concepts based on versions from the MTL draft manual and Boost Graph and Property Map documentation, the SGI Standard Template Library documentation and the Hewlett-Packard STL, under the following license: </p> <div class="blockquote"><blockquote class="blockquote"><p>Permission to use, copy, modify, distribute and sell this software and its documentation for any purpose is hereby granted without fee, provided that the above copyright notice appears in all copies and that both that copyright notice and this permission notice appear in supporting documentation. Silicon Graphics makes no representations about the suitability of this software for any purpose. 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