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< title > The MPL Reference Manual: Bidirectional Iterator< / title >
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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 >
< 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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< 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 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 class = "section" id = "id392" >
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< h3 > < a class = "subsection-title" href = "#definitions" name = "definitions" > Definitions< / a > < / h3 >
< 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"
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
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decrementable.< / li >
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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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< tr > < th class = "head" > Expression< / th >
< th class = "head" > Type< / th >
< th class = "head" > Complexity< / th >
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< / tr >
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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 >
< / tr >
< 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 >
< / tr >
< 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 >
< td > Constant time< / td >
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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 >
< pre class = "literal-block" >
typedef < a href = "./prior.html" class = "identifier" > prior< / a > < i> ::type j;
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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 >
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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 >
< / 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 >
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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 >
< 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 >
is a null operation.< / li >
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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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< td > < div class = "copyright-footer" > < div class = "copyright" > Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams< / div >
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