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< title > Iterator Traits< / title >
< meta name = "author" content = "David Abrahams" / >
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< meta name = "date" content = "2004-11-01" / >
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< div class = "document" id = "iterator-traits" >
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< h1 class = "title" > Iterator Traits< / h1 >
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< tr > < th class = "docinfo-name" > Author:< / th >
< td > David Abrahams< / td > < / tr >
< tr > < th class = "docinfo-name" > Contact:< / th >
< td > < a class = "first last reference" href = "mailto:dave@boost-consulting.com" > dave@ boost-consulting.com< / a > < / td > < / tr >
< tr > < th class = "docinfo-name" > Organization:< / th >
< td > < a class = "first last reference" href = "http://www.boost-consulting.com" > Boost Consulting< / a > < / td > < / tr >
< tr > < th class = "docinfo-name" > Date:< / th >
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< td > 2004-11-01< / td > < / tr >
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< tr > < th class = "docinfo-name" > Copyright:< / th >
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< td > Copyright David Abrahams 2004.< / td > < / tr >
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< tr class = "field" > < th class = "field-name" > abstract:< / th > < td class = "field-body" > Header < tt class = "docutils literal" > < span class = "pre" > < boost/iterator/iterator_traits.hpp> < / span > < / tt > provides
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the ability to access an iterator's associated types using
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MPL-compatible < a class = "reference" href = "../../mpl/doc/refmanual/metafunction.html" > metafunctions< / a > .< / td >
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< div class = "section" id = "overview" >
< h1 > < a name = "overview" > Overview< / a > < / h1 >
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< p > < tt class = "docutils literal" > < span class = "pre" > std::iterator_traits< / span > < / tt > provides access to five associated types
of any iterator: its < tt class = "docutils literal" > < span class = "pre" > value_type< / span > < / tt > , < tt class = "docutils literal" > < span class = "pre" > reference< / span > < / tt > , < tt class = "docutils literal" > < span class = "pre" > pointer< / span > < / tt > ,
< tt class = "docutils literal" > < span class = "pre" > iterator_category< / span > < / tt > , and < tt class = "docutils literal" > < span class = "pre" > difference_type< / span > < / tt > . Unfortunately,
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such a " multi-valued" traits template can be difficult to use in a
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metaprogramming context. < tt class = "docutils literal" > < span class = "pre" > < boost/iterator/iterator_traits.hpp> < / span > < / tt >
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provides access to these types using a standard < a class = "reference" href = "../../mpl/doc/refmanual/metafunction.html" > metafunctions< / a > .< / p >
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< / div >
< div class = "section" id = "summary" >
< h1 > < a name = "summary" > Summary< / a > < / h1 >
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< p > Header < tt class = "docutils literal" > < span class = "pre" > < boost/iterator/iterator_traits.hpp> < / span > < / tt > :< / p >
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< pre class = "literal-block" >
template < class Iterator>
struct iterator_value
{
typedef typename
std::iterator_traits< Iterator> ::value_type
type;
};
template < class Iterator>
struct iterator_reference
{
typedef typename
std::iterator_traits< Iterator> ::reference
type;
};
template < class Iterator>
struct iterator_pointer
{
typedef typename
std::iterator_traits< Iterator> ::pointer
type;
};
template < class Iterator>
struct iterator_difference
{
typedef typename
detail::iterator_traits< Iterator> ::difference_type
type;
};
template < class Iterator>
struct iterator_category
{
typedef typename
detail::iterator_traits< Iterator> ::iterator_category
type;
};
< / pre >
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< div class = "section" id = "broken-compiler-notes" >
< h1 > < a name = "broken-compiler-notes" > Broken Compiler Notes< / a > < / h1 >
< p > Because of workarounds in Boost, you may find that these
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< a class = "reference" href = "../../mpl/doc/refmanual/metafunction.html" > metafunctions< / a > actually work better than the facilities provided by
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your compiler's standard library.< / p >
< p > On compilers that don't support partial specialization, such as
Microsoft Visual C++ 6.0 or 7.0, you may need to manually invoke
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< a class = "reference" href = "../../../doc/html/boost_typetraits/category.html#boost_typetraits.transform" > BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION< / a > on the
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< tt class = "docutils literal" > < span class = "pre" > value_type< / span > < / tt > of pointers that are passed to these metafunctions.< / p >
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< p > Because of bugs in the implementation of GCC-2.9x, the name of
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< tt class = "docutils literal" > < span class = "pre" > iterator_category< / span > < / tt > is changed to < tt class = "docutils literal" > < span class = "pre" > iterator_category_< / span > < / tt > on that
compiler. A macro, < tt class = "docutils literal" > < span class = "pre" > BOOST_ITERATOR_CATEGORY< / span > < / tt > , that expands to
either < tt class = "docutils literal" > < span class = "pre" > iterator_category< / span > < / tt > or < tt class = "docutils literal" > < span class = "pre" > iterator_category_< / span > < / tt > , as
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appropriate to the platform, is provided for portability.< / p >
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