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Apache C++ Standard Library Reference Guide

Bidirectional Iterators

Library:  Iterators

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An iterator that can both read and write and can traverse a container in both directions


NOTE -- For a complete discussion of iterators, see the Iterators section of this reference.

Iterators are a generalization of pointers that allow a C++ program to uniformly interact with different data structures. Bidirectional iterators can move both forwards and backwards through a container, and have the ability to both read and write data. These iterators satisfy the requirements listed below.

Key to Iterator Requirements

The following key pertains to the iterator descriptions listed below:

a and b

values of type X


value representing a distance between two iterators

u, Distance, tmp and m



value of type X&


value of type T

Requirements for Bidirectional Iterators

A bidirectional iterator must meet all the requirements listed below. Note that most of these requirements are also the requirements for forward iterators.

X u

u might have a singular value


X() might be singular


copy constructor, a == X(a)

X u(a)

copy constructor, u == a

X u = a

assignment, u == a

r = a

assignment, r == a

a == b, a != b

return value convertible to bool


equivalent to (*a).m


return value convertible to T&


returns X&


return value convertible to const X&


returns T&


returns X&


return value convertible to const X&


returns T&

Like forward iterators, bidirectional iterators have the condition that a == b implies *a== *b.

There are no restrictions on the number of passes an algorithm may make through the structure.

See Also

Containers, Iterators, Forward Iterators

Standards Conformance

ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 24.1.4

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