C++ In a Nutshell

Name

iterator class template — Iterator base-class template

Synopsis

template<typename Category, typename T, typename Difference = ptrdiff_t,
         typename Pointer = T*, typename Reference = T&>
struct iterator{
  typedef T value_type;
  typedef Difference difference_type;
  typedef Pointer pointer;
  typedef Reference reference;
  typedef Category iterator_category;
};

The iterator class template is a convenient base-class template to use when implementing your own iterator.

The following are the template parameters, which are all type parameters:

Category

Must be one of the five iterator category tags: bidirectional_iterator_tag, forward_iterator_tag, input_iterator_tag, output_iterator_tag, or random_access_iterator_tag.

T

The element type. It can be void for an output iterator because you cannot dereference an output iterator.

Difference

An integral type that represents the distance between two iterators. It can be void for an output iterator because you cannot measure the distance between two output iterators. This parameter is optional; the default is ptrdiff_t, which is suitable for typical pointer-like iterators.

Pointer

The pointer-to-element type. This parameter is optional; the default is T*, which is correct for most iterators.

Reference

The reference-to-element type. This parameter is optional; the default is T&, which is correct for most iterators.

See Also

iterator_traits class template, reverse_iterator class template