Книга: Standard Template Library Programmer

Bidirectional Iterator

Bidirectional Iterator

Category: iterators

Component type: concept

Description

A Bidirectional Iterator is an iterator that can be both incremented and decremented. The requirement that a Bidirectional Iterator can be decremented is the only thing that distinguishes Bidirectional Iterators from Forward Iterators.

Refinement of

Forward Iterator

Associated types

The same as for Forward Iterator.

Notation

X A type that is a model of Bidirectional Iterator

T The value type of X

i, j Object of type X

t Object of type T

Valid expressions

In addition to the expressions defined in Forward Iterator, the following expressions must be valid.

Name  Expression Return type
Predecrement --i X&
Postdecrement i-- X

Expression Semantics

Semantics of an expression is defined only where it is not defined in Forward Iterator.

Name Expression Precondition Semantics Postcondition
Predecrement --i i is dereferenceable or past-the-end. There exists a dereferenceable iterator j such that i == ++j. i is modified to point to the previous element. i is dereferenceable. &i = &--i . If i == j , then --i == --j . If j is dereferenceable and i == ++j , then --i == j.
Postdecrement i-- i is dereferenceable or past-the-end. There exists a dereferenceable iterator j such that i == ++j. Equivalent to { X tmp = i; --i; return tmp; }

Complexity guarantees

The complexity of operations on bidirectional iterators is guaranteed to be amortized constant time.

Invariants

Symmetry of increment and decrement If i is dereferenceable, then ++i; --i; is a null operation. Similarly, --i; ++i; is a null operation.

Models

• T*
• list<T>::iterator

See also

Input Iterator, Output Iterator, Forward Iterator, Random Access Iterator, Iterator overview

Оглавление книги


Генерация: 0.040. Запросов К БД/Cache: 0 / 2
поделиться
Вверх Вниз