# operator-(std::reverse_iterator)

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< cpp‎ | iterator‎ | reverse iterator

Defined in header `<iterator>` |  |
template< class Iter1, class Iter2 > typename reverse_iterator<Iter>::difference_type operator-( const reverse_iterator<Iter1>& lhs, const reverse_iterator<Iter2>& rhs ); |  | (until C++11)
template< class Iter1, class Iter2 > auto operator-( const reverse_iterator<Iter1>& lhs, const reverse_iterator<Iter2>& rhs ) -> decltype(rhs.base() - lhs.base()); |  | (since C++11) (constexpr since C++17)

Returns the distance between two iterator adaptors.

### Parameters

lhs, rhs | - | iterator adaptors to compute the difference of

### Return value

rhs.base() - lhs.base()

### Notes

operator- returns rhs.base() - lhs.base() rather than lhs.base() - rhs.base() because this is a reverse iterator.

### Example

Run this code

    #include <iostream>
    #include <iterator>
    #include <list>
    #include <vector>

    int main()
    {
        std::vector vec{0, 1, 2, 3};
        std::reverse_iterator<std::vector<int>::iterator>
            vec_ri1{std::reverse_iterator{vec.rbegin()}},
            vec_ri2{std::reverse_iterator{vec.rend()}};
        std::cout << (vec_ri2 - vec_ri1) << ' '; // 4
        std::cout << (vec_ri1 - vec_ri2) << '\n'; // -4

        std::list lst{5, 6, 7, 8};
        std::reverse_iterator<std::list<int>::iterator>
            lst_ri1{std::reverse_iterator{lst.rbegin()}},
            lst_ri2{std::reverse_iterator{lst.rend()}};
    //  auto n = (lst_ri1 - lst_ri2); // Error: the underlying iterators do not
                                      //        model random access iterator
    }

Output:

    4 -4

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 280 | C++98 | heterogeneous subtraction was not allowed | allowed

### See also

operator++operator++(int)operator+=operator+operator--operator--(int)operator-=operator- | advances or decrements the iterator (public member function)
operator+ | advances the iterator (function template)

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