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.