__iterator_category(3C++) - __iterator_category(3C++)
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 sup‐
port 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 func‐
tion 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 TYPESinput_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagThe __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 sac‐
rificing 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 toselect 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-directional
// capability of the iterators
}
See the iterator section for a description of iterators and the capabilitiesassociated with each type of iterator tag.SEE ALSO
Other iterator primitives: __distance_type, distance, advance, itera‐
tor
Rogue Wave Software 02 Apr 1998 __iterator_category(3C++)