Reversible Container

Category: containers Component type: concept


A Reversible Container is a Forward Container whose iterators are Bidirectional Iterators. It allows backwards iteration through the container.

Refinement of

Forward Container

Associated types

Two new types are introduced. In addition, the iterator type and the const iterator type must satisfy a more stringent requirement than for a Forward Container. The iterator and reverse iterator types must be Bidirectional Iterators, not merely Forward Iterators.
Reverse iterator type X::reverse_iterator A Reverse Iterator adaptor whose base iterator type is the container's iterator type. Incrementing an object of type reverse_iterator moves backwards through the container: the Reverse Iterator adaptor maps operator++ to operator--.
Const reverse iterator type X::const_reverse_iterator A Reverse Iterator adaptor whose base iterator type is the container's const iterator type. [1]


X A type that is a model of Reversible Container
a, b Object of type X


Valid expressions

In addition to the expressions defined in Forward Container, the following expressions must be valid.
Name Expression Type requirements Return type
Beginning of range a.rbegin()   reverse_iterator if a is mutable, const_reverse_iterator otherwise [1]
End of range a.rend()   reverse_iterator if a is mutable, const_reverse_iterator otherwise [1]

Expression semantics

Semantics of an expression is defined only where it is not defined in Forward Container, or where there is additional information.
Name Expression Precondition Semantics Postcondition
Beginning of reverse range a.rbegin()   Equivalent to X::reverse_iterator(a.end()). a.rbegin() is dereferenceable or past-the-end. It is past-the-end if and only if a.size() == 0.
End of reverse range a.rend()   Equivalent to X::reverse_iterator(a.begin()). a.end() is past-the-end.

Complexity guarantees

The run-time complexity of rbegin() and rend() is amortized constant time.


Valid range [a.rbegin(), a.rend()) is a valid range.
Equivalence of ranges The distance from a.begin() to a.end() is the same as the distance from a.rbegin() to a.rend().



[1] A Container's iterator type and const iterator type may be the same type: a container need not provide mutable iterators. It follows from this that the reverse iterator type and the const reverse iterator type may also be the same.

See also

The Iterator overview, Bidirectional Iterator, Sequence
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