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| <title>The MPL Reference Manual: Bidirectional Iterator</title> |
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| <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> |
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| <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> |
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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> |
| </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> |
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| </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> |
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