Next : Random access iterators, Previous : Forward iterators, Top : Table of Contents

Bidirectional iterators

-- Operator on bidirectional iterators

A class or a built-in type X satisfies the requirements of a bidirectional iterator if the following lines are added to the table that specifies forward iterators:

Table 5: Bidirectional iterator requirements (in addition to forward iterator)

Expression Return type Operational semantics Assertion/note pre/post-condition

--r X& pre: there exists s such that
r == ++s.
post: s is dereferenceable.
--(++r) == r.
--r == --s implies r == s.
&r == &--r.

r-- X
{ X tmp = r; --r; return tmp; }

NOTE: Bidirectional iterators allow algorithms to move iterators backward as well as forward.

Expression	Return type	Operational semantics	Assertion/note pre/post-condition
--r	X&		pre: there exists s such that r == ++s. post: s is dereferenceable. --(++r) == r. --r == --s implies r == s. &r == &--r.
r--	X	{ X tmp = r; --r; return tmp; }