iterator_category (3C++std) - Tru64 UNIX
Standard C++ LibraryCopyright 1996, Rogue Wave Software, Inc. NAME
iterator_category - Determines the category that an iterator belongs to.
This function is now obsolete. It is retained in order to provide backward
compatibility and support compilers that do not provide partial
specialization.
SYNOPSIS
#include <iterator>
template <class T, class Distance>
inline input_iterator_tag
iterator_category (const input_iterator<T, Distance>&)
inline output_iterator_tag iterator_category (const output_iterator&)
template <class T, class Distance>
inline forward_iterator_tag
iterator_category (const forward_iterator<T, Distance>&)
template <class T, class Distance>
inline bidirectional_iterator_tag
iterator_category (const bidirectional_iterator<T, Distance>&)
template <class T, class Distance>
inline random_access_iterator_tag
iterator_category (const random_access_iterator<T, Distance>&)
template <class T>
inline random_access_iterator_tag iterator_category (const T*)
DESCRIPTION
The iterator_category family of function templates allows you to determine
the category that any iterator belongs to. The first five functions take
an iterator of a specific type and return the tag for that type. The last
takes a T* and returns random_access_iterator_tag.
TAG TYPES
input_iterator_tag
output_iterator_tag
forward_iterator_tag
bidirectional_iterator_tag
random_access_iterator_tag
The iterator_category function is particularly useful for improving the
efficiency of algorithms. An algorithm can use this function to select the
most efficient implementation an iterator is capable of handling without
sacrificing the ability to work with a wide range of iterator types. For
instance, both the advance and distance primitives use iterator_category to
maximize their efficiency by using the tag returned from iterator_category
to select from one of several different auxiliary functions. Because this
is a compile time selection, use of this primitive incurs no significant
runtime overhead.
iterator_category is typically used like this:
template <class Iterator>
void foo(Iterator first, Iterator last)
{
__foo(begin,end,iterator_category(first));
}
template <class Iterator>
void __foo(Iterator first, Iterator last,
input_iterator_tag>
{
// Most general implementation
}
template <class Iterator>
void __foo(Iterator first, Iterator last,
bidirectional_iterator_tag>
{
// Implementation takes advantage of bi-diretional
// capability of the iterators
}
_etc.
See the iterator section in the Class Reference for a description of
iterators and the capabilities associated with each type of iterator tag.
SEE ALSO
Other iterator primitives: value_type, distance_type, distance,advance,
iterator
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
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