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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