SGI

forward_iterator<T Distance>

Category: iterators Component type: type

Description

Forward_iterator is an iterator base class: it is intended that an iterator that is a model of Forward Iterator and whose value type and distance type are T and Distance may be defined by inheriting from forward_iterator<T Distance> [1]. Forward_iterator is entirely empty: it has no member functions member variables or nested types. It exists solely to simplify the definition of the functions iterator_category distance_type and value_type.

Example

class my_forward_iterator : public forward_iterator<double>
{
  ...
};
This declares my_forward_iterator to be a Forward Iterator whose value type is double and whose distance type is ptrdiff_t. If Iter is an object of class my_forward_iterator then iterator_category(Iter) will return forward_iterator_tag() value_type(Iter) will return (double*) 0 and distance_type(Iter) will return (ptrdiff_t*) 0.

Definition

Defined in the standard header iterator and in the nonstandard backward-compatibility header iterator.h. This class is no longer part of the C++ standard although it was present in early drafts of the standard. It is retained in this implementation for backward compatibility.

Template parameters

Parameter Description Default
T The iterator's value type  
Distance The iterator's distance type ptrdiff_t

Model of

Assignable

Public base classes

None

Type requirements

The distance type must be a signed integral type.

Public base classes

None.

Members

None.

New Members

None.

Notes

[1] It is not required that a Forward Iterator inherit from the base forward_iterator. It is however required that the functions iterator_category distance_type and value_type be defined for every Forward Iterator. (Or if you are using the iterator_traits mechanism that iterator_traits is properly specialized for every Forward Iterator.) Since those functions are defined for the base forward_iterator the easiest way to ensure that are defined for a new type is to derive that class from forward_iterator and rely on the derived-to-base standard conversion of function arguments.

See also

The Iterator Tags overview iterator_traits iterator_category value_type distance_type input_iterator output_iterator bidirectional_iterator random_access_iterator
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