Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.
NAME
__iterator_category
- Determines the category to which an iterator belongs.
This function is now obsolete. It is included for backward
compatibility and to support compilers that do not include
partial specialization.
SYNOPSIS
#include <iterator>
template <class Category, class T, class Distance,
class Pointer, class Reference>
inline Category __iterator_category
(const iterator<Category, T, Distance, Pointer,
Reference>&);
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 to which any iterator belongs.
The first function takes an iterator of a specific type and
returns 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 sig-
nificant 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-directional
// capability of the iterators
}
See the iterator section for a description of iterators and
the capabilities associated with each type of iterator tag.
SEE ALSO
Other iterator primitives: __distance_type, distance,
advance, iterator