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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