109 lines
8.4 KiB
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109 lines
8.4 KiB
HTML
<?xml version="1.0" encoding="utf-8" ?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" />
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<title>The MPL Reference Manual: Bidirectional Iterator</title>
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</head>
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<body class="docframe refmanual">
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<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>
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<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>
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</tr></table><div class="header-separator"></div>
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<div class="section" id="bidirectional-iterator">
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<h1><a class="toc-backref" href="./iterators-concepts.html#id1451">Bidirectional Iterator</a></h1>
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<div class="section" id="id390">
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<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
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<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
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obtain an iterator to the previous element in a sequence.</p>
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</div>
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<div class="section" id="id391">
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<h3><a class="subsection-title" href="#refinement-of" name="refinement-of">Refinement of</a></h3>
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<p><a class="reference internal" href="./forward-iterator.html">Forward Iterator</a></p>
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</div>
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<div class="section" id="id392">
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<h3><a class="subsection-title" href="#definitions" name="definitions">Definitions</a></h3>
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<ul class="simple">
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<li>a bidirectional iterator <tt class="literal"><span class="pre">i</span></tt> is <cite>decrementable</cite> if there is a "previous"
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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;
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iterators pointing to the first element of the sequence are not
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decrementable.</li>
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</ul>
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</div>
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<div class="section" id="id393">
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<h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3>
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<p>In addition to the requirements defined in <a class="reference internal" href="./forward-iterator.html">Forward Iterator</a>,
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the following requirements must be met.</p>
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<table border="1" class="docutils table">
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<colgroup>
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<col width="25%" />
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<col width="46%" />
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</colgroup>
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<thead valign="bottom">
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<tr><th class="head">Expression</th>
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<th class="head">Type</th>
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<th class="head">Complexity</th>
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</tr>
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</thead>
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<tbody valign="top">
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<tr><td><tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a><i>::type</span></tt></td>
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<td><a class="reference internal" href="./bidirectional-iterator.html">Bidirectional Iterator</a></td>
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<td>Amortized constant time</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre"><a href="./prior.html" class="identifier">prior</a><i>::type</span></tt></td>
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<td><a class="reference internal" href="./bidirectional-iterator.html">Bidirectional Iterator</a></td>
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<td>Amortized constant time</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre">i::category</span></tt></td>
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<td><a class="reference internal" href="./integral-constant.html">Integral Constant</a>, convertible
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to <tt class="literal"><span class="pre">bidirectional_iterator_tag</span></tt></td>
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<td>Constant time</td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="section" id="id394">
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<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
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<pre class="literal-block">
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typedef <a href="./prior.html" class="identifier">prior</a><i>::type j;
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</pre>
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<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>
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</tr>
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<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
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sequence</td>
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</tr>
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<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>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="section" id="id395">
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<h3><a class="subsection-title" href="#invariants" name="invariants">Invariants</a></h3>
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<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
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always hold:</p>
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<ul class="simple">
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<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
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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>
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is a null operation.</li>
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</ul>
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</div>
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<div class="section" id="id396">
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<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
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<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>
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<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>
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<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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>
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