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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 = "2004-01-12" />
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< div class = "document" id = "counting-iterator" >
< h1 class = "title" > Counting Iterator</ h1 >
< table class = "docinfo" frame = "void" rules = "none" >
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< col class = "docinfo-content" />
< tbody valign = "top" >
< 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 > 2004-01-12</ 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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</ tbody >
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< tr class = "field" >< th class = "field-name" > abstract:</ th >< td class = "field-body" ></ td >
</ tr >
</ tbody >
</ table >
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< p >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > adapts an arithmetic type, such as < tt class = "literal" >< span class = "pre" > int</ span ></ tt > , by
adding an < tt class = "literal" >< span class = "pre" > operator*</ span ></ tt > that returns the current value of the object.</ p >
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< 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" >
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< li >< a class = "reference" href = "#counting-iterator-synopsis" id = "id2" name = "id2" >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > synopsis</ a ></ li >
< li >< a class = "reference" href = "#counting-iterator-requirements" id = "id3" name = "id3" >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > requirements</ a ></ li >
< li >< a class = "reference" href = "#counting-iterator-models" id = "id4" name = "id4" >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > models</ a ></ li >
< li >< a class = "reference" href = "#counting-iterator-operations" id = "id5" name = "id5" >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > operations</ a ></ li >
< li >< a class = "reference" href = "#example" id = "id6" name = "id6" > Example</ a ></ li >
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</ ul >
</ div >
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< div class = "section" id = "counting-iterator-synopsis" >
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< h1 >< a class = "toc-backref" href = "#id2" name = "counting-iterator-synopsis" >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > synopsis</ a ></ h1 >
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< pre class = "literal-block" >
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template <
class Incrementable
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, class CategoryOrTraversal = use_default
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, class Difference = use_default
>
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class counting_iterator
{
public:
counting_iterator();
counting_iterator(counting_iterator const& rhs);
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explicit counting_iterator(Incrementable x);
Incrementable base() const;
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reference operator*() const;
counting_iterator& operator++();
counting_iterator& operator--();
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private:
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Incrementable m_inc; // exposition
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};
</ 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 >
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</ div >
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< div class = "section" id = "counting-iterator-requirements" >
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< h1 >< a class = "toc-backref" href = "#id3" name = "counting-iterator-requirements" >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > requirements</ a ></ h1 >
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< p > The < tt class = "literal" >< span class = "pre" > Incrementable</ span ></ tt > type must be Default Constructible, Copy
Constructible, and Assignable. The default distance is
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an implementation defined signed integral type.</ p >
</ div >
< div class = "section" id = "counting-iterator-models" >
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< h1 >< a class = "toc-backref" href = "#id4" name = "counting-iterator-models" >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > models</ a ></ h1 >
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< p >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > models Readable Lvalue Iterator.</ p >
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< 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" >
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< h1 >< a class = "toc-backref" href = "#id5" name = "counting-iterator-operations" >< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > operations</ a ></ h1 >
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< p > In addition to the operations required by the concepts modeled by
< tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > , < tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > provides the following
operations.</ p >
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< p >< tt class = "literal" >< span class = "pre" > counting_iterator();</ 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" > 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 >
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< p >< tt class = "literal" >< span class = "pre" > explicit</ span > < span class = "pre" > counting_iterator(Incrementable</ span > < span class = "pre" > x);</ span ></ tt ></ p >
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< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" />
< col class = "field-body" />
< tbody valign = "top" >
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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 < tt class = "literal" >< span class = "pre" > m_inc</ span ></ tt >
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constructed from < tt class = "literal" >< span class = "pre" > x</ span ></ tt > .</ td >
</ tr >
</ tbody >
</ table >
< p >< tt class = "literal" >< span class = "pre" > reference</ span > < span class = "pre" > operator*()</ span > < span class = "pre" > const;</ span ></ tt ></ p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" />
< col class = "field-body" />
< tbody valign = "top" >
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< tr class = "field" >< th class = "field-name" > Returns:</ th >< td class = "field-body" >< tt class = "literal" >< span class = "pre" > m_inc</ span ></ tt ></ td >
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</ tr >
</ tbody >
</ table >
< p >< tt class = "literal" >< span class = "pre" > counting_iterator& </ span > < span class = "pre" > operator++();</ span ></ tt ></ p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" />
< col class = "field-body" />
< tbody valign = "top" >
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< tr class = "field" >< th class = "field-name" > Effects:</ th >< td class = "field-body" >< tt class = "literal" >< span class = "pre" > ++m_inc</ span ></ tt ></ td >
</ tr >
< tr class = "field" >< th class = "field-name" > Returns:</ th >< td class = "field-body" >< tt class = "literal" >< span class = "pre" > *this</ span ></ tt ></ td >
</ tr >
</ tbody >
</ table >
< p >< tt class = "literal" >< span class = "pre" > counting_iterator& </ span > < span class = "pre" > operator--();</ 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" > Effects:</ th >< td class = "field-body" >< tt class = "literal" >< span class = "pre" > --m_inc</ span ></ tt ></ td >
</ tr >
< tr class = "field" >< th class = "field-name" > Returns:</ th >< td class = "field-body" >< tt class = "literal" >< span class = "pre" > *this</ span ></ tt ></ td >
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</ tr >
</ tbody >
</ table >
< p >< tt class = "literal" >< span class = "pre" > Incrementable</ span > < span class = "pre" > base()</ span > < span class = "pre" > const;</ span ></ tt ></ p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" />
< col class = "field-body" />
< tbody valign = "top" >
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< tr class = "field" >< th class = "field-name" > Returns:</ th >< td class = "field-body" >< tt class = "literal" >< span class = "pre" > m_inc</ span ></ tt ></ td >
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</ tr >
</ tbody >
</ table >
< pre class = "literal-block" >
template < class Incrementable>
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counting_iterator< Incrementable> make_counting_iterator(Incrementable x);
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</ pre >
< 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< Incrementable> </ span ></ tt >
with < tt class = "literal" >< span class = "pre" > current</ span ></ tt > constructed from < tt class = "literal" >< span class = "pre" > x</ span ></ tt > .</ td >
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</ tr >
</ tbody >
</ table >
</ div >
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< div class = "section" id = "example" >
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< h1 >< a class = "toc-backref" href = "#id6" name = "example" > Example</ a ></ h1 >
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< p > This example fills an array with numbers and a second array with
pointers into the first array, using < tt class = "literal" >< span class = "pre" > counting_iterator</ span ></ tt > for both
tasks. Finally < tt class = "literal" >< span class = "pre" > indirect_iterator</ span ></ tt > is used to print out the numbers
into the first array via indirection through the second array.</ p >
< pre class = "literal-block" >
int N = 7;
std::vector< int> numbers;
typedef std::vector< int> ::iterator n_iter;
std::copy(boost::counting_iterator< int> (0),
boost::counting_iterator< int> (N),
std::back_inserter(numbers));
std::vector< std::vector< int> ::iterator> pointers;
std::copy(boost::make_counting_iterator(numbers.begin()),
boost::make_counting_iterator(numbers.end()),
std::back_inserter(pointers));
std::cout << " indirectly printing out the numbers from 0 to "
<< N << std::endl;
std::copy(boost::make_indirect_iterator(pointers.begin()),
boost::make_indirect_iterator(pointers.end()),
std::ostream_iterator< int> (std::cout, " " ));
std::cout << std::endl;
</ pre >
< p > The output is:</ p >
< pre class = "literal-block" >
indirectly printing out the numbers from 0 to 7
0 1 2 3 4 5 6
</ pre >
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< p > The source code for this example can be found < a class = "reference" href = "../example/counting_iterator_example.cpp" > here</ a > .</ p >
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</ div >
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</ div >
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