Standard C++ Library Class Reference

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 Iterators section in the Class Reference for a description of iterators and the capabilities
associated with each type of iterator tag.