# std::reverse_iterator

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< cpp‎ | iterator

Defined in header `<iterator>` |  |
template< class Iterator > class reverse_iterator : public std::iterator< typename std::iterator_traits<Iterator>::iterator_category, typename std::iterator_traits<Iterator>::value_type, typename std::iterator_traits<Iterator>::difference_type, typename std::iterator_traits<Iterator>::pointer, typename std::iterator_traits<Iterator>::reference > |  | (until C++17)
template< class Iterator > class reverse_iterator; |  | (since C++17)

`std::reverse_iterator` is an iterator adaptor that reverses the direction of a given iterator. In other words, when provided with a bidirectional iterator, `std::reverse_iterator` produces a new iterator that moves from the end to the beginning of the sequence defined by the underlying bidirectional iterator.

For a reverse iterator `r` constructed from an iterator `i`, the relationship &*r == &*(i-1) is always true (as long as `r` is dereferenceable); thus a reverse iterator constructed from a one-past-the-end iterator dereferences to the last element in a sequence.

This is the iterator returned by member functions `rbegin()` and `rend()` of the standard library containers.

### Member types

Member type | Definition
`value_type` | std::iterator_traits<Iterator>::value_type
`difference_type` | std::iterator_traits<Iterator>::difference_type
`pointer` | std::iterator_traits<Iterator>::pointer
`reference` | std::iterator_traits<Iterator>::reference
`iterator_category` | std::iterator_traits<Iterator>::iterator_category

Note: before C++17, these member types are required to be obtained by inheriting from std::iterator< std::iterator_traits<Iterator>::iterator_category
, std::iterator_traits<Iterator>::value_type
, std::iterator_traits<Iterator>::difference_type
, std::iterator_traits<Iterator>::pointer
, std::iterator_traits<Iterator>::reference
>.

Member type | Definition
`iterator_type` | `Iterator`

### Member functions

(constructor) | constructs a new iterator adaptor (public member function)
operator= | assigns another iterator (public member function)
base | accesses the underlying iterator (public member function)
operator*operator-> | accesses the pointed-to element (public member function)
operator[] | accesses an element by index (public member function)
operator++operator++(int)operator+=operator+operator--operator--(int)operator-=operator- | advances or decrements the iterator (public member function)

### Member objects

Member name | Definition
`current` (protected) | a copy of the base() iterator

### Non-member functions

operator==operator!=operator<operator<=operator>operator>= | compares the underlying iterators (function template)
operator+ | advances the iterator (function template)
operator- | computes the distance between two iterator adaptors (function template)

### Example

Run this code

    #include <iostream>
    #include <string>
    #include <iterator>

    int main()
    {
        std::string s = "Hello, world";
        std::reverse_iterator<std::string::iterator> r = s.rbegin();
        r[7] = 'O'; // replaces 'o' with 'O'
        r += 7; // iterator now points at 'O'
        std::string rev(r, s.rend());
        std::cout << rev << '\n';
    }

Output:

    OlleH

### See also

iterator (deprecated in C++17) | base class to ease the definition of required types for simple iterators (class template)

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