Книга: Standard Template Library Programmer

bidirectional_iterator

bidirectional_iterator<T, Distance>

Category: iterators

Component type: type

Bidirectional_iterator is an iterator base class: it is intended that an iterator that is a model of Bidirectional Iterator, and whose value type and distance type are T and Distance, may be defined by inheriting from bidirectional_iterator<T, Distance> [1]. Bidirectional_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.

class my_bidirectional_iterator : public bidirectional_iterator<double> {
 …
};

This declares my_bidirectional_iterator to be a Bidirectional Iterator whose value type is double and whose distance type is ptrdiff_t. If Iter is an object of class my_bidirectional_iterator, then iterator_category(Iter) will return bidirectional_iterator_tag(), value_type(Iter) will return (double*)0, and distance_type(Iter) will return (ptrdiff_t*)0.

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.

Assignable

None

The distance type must be a signed integral type.

None.

None.

None.

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

The Iterator Tags overview, iterator_traits, iterator_category, value_type, distance_type, input_iterator, output_iterator, forward_iterator, random_access_iterator

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