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AReversibleContainer is aContainer that has iterators that meet the requirements of eitherLegacyBidirectionalIterator orLegacyRandomAccessIterator. Such iterators allow aReversibleContainer to be iterated over in reverse.
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A type satisfiesReversibleContainer if it satisfiesContainer, its iterator type belongs to the bidirectional or random accessiterator categories and, given the following types and values, the semantic and complexity requirements in the tables below are satisfied:
| Type | Definition |
X | anReversibleContainer type |
T | thevalue_type ofX |
| Value | Definition |
| a | a value of typeX |
| Name | Type | Requirements |
|---|---|---|
| typename X::reverse_iterator | std::reverse_iterator<X::iterator> | an iterator type whosevalue type isT |
| typename X::const_reverse_iterator | std::reverse_iterator<X::const_iterator> | a constant iterator type whosevalue type isT |
The typesreverse_iterator andconst_reverse_iterator in the following table denotetypename X::reverse_iterator andtypename X::const_reverse_iterator respectively.
| Expression | Type | Semantics | Complexity |
|---|---|---|---|
| a.rbegin() | reverse_iteratorconst_reverse_iterator for constanta | reverse_iterator(a.end()) | Constant |
| a.rend() | reverse_iteratorconst_reverse_iterator for constanta | reverse_iterator(a.begin()) | Constant |
| a.crbegin() | const_reverse_iterator | const_cast<const X&>(a).rbegin() | Constant |
| a.crend() | const_reverse_iterator | const_cast<const X&>(a).rend() | Constant |
The following standard library types satisfyReversibleContainer requirements:
(C++11) | fixed-sized inplace contiguous array (class template)[edit] |
| double-ended queue (class template)[edit] | |
| doubly-linked list (class template)[edit] | |
| resizable contiguous array (class template)[edit] | |
(C++26) | resizable, fixed capacity, inplace contiguous array (class template)[edit] |
| collection of key-value pairs, sorted by keys, keys are unique (class template)[edit] | |
| collection of key-value pairs, sorted by keys (class template)[edit] | |
| collection of unique keys, sorted by keys (class template)[edit] | |
| collection of keys, sorted by keys (class template)[edit] |
The following example iterates over avector (which haslegacy random-access iterators) in reverse.
#include <iostream>#include <vector> int main(){std::vector<int> v={3,1,4,1,5,9}; for(std::vector<int>::const_reverse_iterator i{v.crbegin()}; i!= v.crend();++i)std::cout<<*i<<' ';std::cout<<'\n';}
Output:
9 5 1 4 1 3
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2105 | C++98 | typename X::const_reverse_iterator was required to be an iterator type of value typeconst T | required to be a constant iterator type of value type T |
