24 Containers library [containers]

24.2 Requirements [container.requirements]

24.2.2 General containers [container.requirements.general]

24.2.2.3 Reversible container requirements [container.rev.reqmts]

A type X meets the reversible container requirements if X meets the container requirements, the iterator type of X belongs to the bidirectional or random access iterator categories ([iterator.requirements]), and the following types and expressions are well-formed and have the specified semantics.
typename X::reverse_iterator
Result: The type reverse_iterator<X​::​iterator>, an iterator type whose value type is T.
typename X::const_reverse_iterator
Result: The type reverse_iterator<X​::​const_iterator>, a constant iterator type whose value type is T.
a.rbegin()
Result: reverse_iterator; const_reverse_iterator for constant a.
Returns: reverse_iterator(end())
Complexity: Constant.
a.rend()
Result: reverse_iterator; const_reverse_iterator for constant a.
Returns: reverse_iterator(begin())
Complexity: Constant.
a.crbegin()
Result: const_reverse_iterator.
Returns: const_cast<X const&>(a).rbegin()
Complexity: Constant.
a.crend()
Result: const_reverse_iterator.
Returns: const_cast<X const&>(a).rend()
Complexity: Constant.