C++ concepts: BidirectionalIterator

A BidirectionalIterator is a ForwardIterator that can be moved in both directions (i.e. incremented and decremented).

Requirements

The type It satisfies BidirectionalIterator if.

• The type It satisfies ForwardIterator

And, given.

• a and b, iterators of type It
• reference, the type denoted by std::iterator_traits<It>::reference

The following expressions must be valid and have their specified effects.

Expression	Return	Equivalent expression	Notes
--a	It&		Preconditions: a is decrementable (there exists such b that a == ++b) Postconditions: a is dereferenceable --(++a) == a If --a == --b then a == b &a == &--a
a--	convertible to const It&	It temp = a; --a; return temp;
*a--	reference

A mutable BidirectionalIterator is a BidirectionalIterator that additionally satisfies the OutputIterator requirements.

Notes

The begin iterator is not decrementable and the behavior is undefined if --container.begin() is evaluated.

A bidirectional iterator does not have to be dereferenceable to be decrementable (in particular, the end iterator is not dereferenceable but is decrementable).

See also

• Iterator library