template< class Iterator1, class Iterator2 >
typename reverse_iterator<Iterator1>::difference_type
operator-( const reverse_iterator<Iterator1>& lhs,
const reverse_iterator<Iterator2>& rhs );
| (until C++11) | |
template< class Iterator1, class Iterator2 >
auto operator-( const reverse_iterator<Iterator1>& lhs,
const reverse_iterator<Iterator2>& rhs
) -> decltype(rhs.base() - lhs.base());
| (since C++11) (until C++17) | |
template< class Iterator1, class Iterator2 >
constexpr auto operator-( const reverse_iterator<Iterator1>& lhs,
const reverse_iterator<Iterator2>& rhs
) -> decltype(rhs.base() - lhs.base());
| (since C++17) |
Returns the distance between two iterator adaptors.
| lhs, rhs | - | iterator adaptors to compute the difference of |
rhs.base() - lhs.base().
#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 the random access iterators
}Output:
4 -4
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 | subtrction between std::reverse_iterator with different underlying iterator types was not allowed | allowed |
| advances or decrements the iterator (public member function) |
|
| advances the iterator (function template) |
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