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< title > Counting Iterator</ title >
< meta name = "author" content = "David Abrahams, Jeremy Siek, Thomas Witt" />
< meta name = "organization" content = "Boost Consulting, Indiana University Open Systems Lab, University of Hanover Institute for Transport Railway Operation and Construction" />
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< meta name = "date" content = "2003-09-14" />
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< h1 class = "title" > Counting Iterator</ h1 >
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< tr >< th class = "docinfo-name" > Author:</ th >
< td > David Abrahams, Jeremy Siek, Thomas Witt</ td ></ tr >
< tr >< th class = "docinfo-name" > Contact:</ th >
< td >< a class = "first reference" href = "mailto:dave@boost-consulting.com" > dave@ boost-consulting.com</ a > , < a class = "reference" href = "mailto:jsiek@osl.iu.edu" > jsiek@ osl.iu.edu</ a > , < a class = "last reference" href = "mailto:witt@ive.uni-hannover.de" > witt@ ive.uni-hannover.de</ a ></ td ></ tr >
< tr >< th class = "docinfo-name" > Organization:</ th >
< td >< a class = "first reference" href = "http://www.boost-consulting.com" > Boost Consulting</ a > , Indiana University < a class = "reference" href = "http://www.osl.iu.edu" > Open Systems
Lab</ a > , University of Hanover < a class = "last reference" href = "http://www.ive.uni-hannover.de" > Institute for Transport
Railway Operation and Construction</ a ></ td ></ tr >
< tr >< th class = "docinfo-name" > Date:</ th >
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< td > 2003-09-14</ td ></ tr >
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< tr >< th class = "docinfo-name" > Copyright:</ th >
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< td > Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved</ td ></ tr >
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< tr class = "field" >< th class = "field-name" > abstract:</ th >< td class = "field-body" ></ td >
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< p > The counting iterator adaptor implements dereference by returning a
reference to the base object. The other operations are implemented by
the base < tt class = "literal" >< span class = "pre" > m_iterator</ span ></ tt > , as per the inheritance from
< tt class = "literal" >< span class = "pre" > iterator_adaptor</ span ></ tt > .</ p >
< div class = "contents topic" id = "table-of-contents" >
< p class = "topic-title" >< a name = "table-of-contents" > Table of Contents</ a ></ p >
< ul class = "simple" >
< li >< a class = "reference" href = "#counting-iterator-requirements" id = "id1" name = "id1" >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > requirements</ a ></ li >
< li >< a class = "reference" href = "#counting-iterator-operations" id = "id2" name = "id2" >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > operations</ a ></ li >
</ ul >
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< pre class = "literal-block" >
template < class Incrementable, class Category = use_default, class Difference = use_default>
class counting_iterator
: public iterator_adaptor<
counting_iterator< Incrementable, Category, Difference>
, Incrementable
, Incrementable
, /* see details for category */
, Incrementable const&
, Incrementable const*
, /* distance = Difference or a signed integral type */>
{
friend class iterator_core_access;
public:
counting_iterator();
counting_iterator(counting_iterator const& rhs);
counting_iterator(Incrementable x);
private:
typename counting_iterator::reference dereference() const
{
return this-> base_reference();
}
};
</ pre >
< dl >
< dt > [< em > Note:</ em > implementers are encouraged to provide an implementation of</ dt >
< dd >< tt class = "literal" >< span class = "pre" > distance_to</ span ></ tt > and a < tt class = "literal" >< span class = "pre" > difference_type</ span ></ tt > that avoids overflows in
the cases when the < tt class = "literal" >< span class = "pre" > Incrementable</ span ></ tt > type is a numeric type.]</ dd >
</ dl >
< div class = "section" id = "counting-iterator-requirements" >
< h1 >< a class = "toc-backref" href = "#id1" name = "counting-iterator-requirements" >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > requirements</ a ></ h1 >
< p > The < tt class = "literal" >< span class = "pre" > Incrementable</ span ></ tt > type must be Default Constructible, Copy
Constructible, and Assignable. The default distance is
an implementation defined signed integegral type.</ p >
< p > The resulting < tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > models Readable Lvalue Iterator.</ p >
< p > Furthermore, if you wish to create a counting iterator that is a Forward
Traversal Iterator, then the following expressions must be valid:</ p >
< pre class = "literal-block" >
Incrementable i, j;
++i // pre-increment
i == j // operator equal
</ pre >
< p > If you wish to create a counting iterator that is a
Bidirectional Traversal Iterator, then pre-decrement is also required:</ p >
< pre class = "literal-block" >
--i
</ pre >
< p > If you wish to create a counting iterator that is a Random Access
Traversal Iterator, then these additional expressions are also
required:</ p >
< pre class = "literal-block" >
counting_iterator::difference_type n;
i += n
n = i - j
i < j
</ pre >
</ div >
< div class = "section" id = "counting-iterator-operations" >
< h1 >< a class = "toc-backref" href = "#id2" name = "counting-iterator-operations" >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > operations</ a ></ h1 >
< p >< tt class = "literal" >< span class = "pre" > counting_iterator();</ span ></ tt ></ p >
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< tr class = "field" >< th class = "field-name" > Returns:</ th >< td class = "field-body" > A default constructed instance of < tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > .</ td >
</ tr >
</ tbody >
</ table >
< p >< tt class = "literal" >< span class = "pre" > counting_iterator(counting_iterator</ span > < span class = "pre" > const& </ span > < span class = "pre" > rhs);</ span ></ tt ></ p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" />
< col class = "field-body" />
< tbody valign = "top" >
< tr class = "field" >< th class = "field-name" > Returns:</ th >< td class = "field-body" > An instance of < tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > that is a copy of < tt class = "literal" >< span class = "pre" > rhs</ span ></ tt > .</ td >
</ tr >
</ tbody >
</ table >
< p >< tt class = "literal" >< span class = "pre" > counting_iterator(Incrementable</ span > < span class = "pre" > x);</ span ></ tt ></ p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" />
< col class = "field-body" />
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< tr class = "field" >< th class = "field-name" > Returns:</ th >< td class = "field-body" > An instance of < tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > with its base
object copy constructed from < tt class = "literal" >< span class = "pre" > x</ span ></ tt > .</ td >
</ tr >
</ tbody >
</ table >
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