template <class Iterator> typename reverse_iterator<Iterator>::difference_type operator- ( const reverse_iterator<Iterator>& lhs, const reverse_iterator<Iterator>& rhs);
template <class Iterator1, class Iterator2> auto operator- (const reverse_iterator<Iterator>& lhs, const reverse_iterator<Iterator>& rhs) -> decltype (rhs.base()-lhs.base()) { return rhs.base()-lhs.base(); }1
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// operator- on reverse_iterator
#include <iostream> // std::cout
#include <iterator> // std::reverse_iterator
#include <vector> // std::vector
int main () {
std::vector<int> myvector;
for (int i=0; i<10; i++) myvector.push_back(i);
std::reverse_iterator<std::vector<int>::iterator> from,until;
from = myvector.rbegin();
until = myvector.rend();
std::cout << "myvector has " << (until-from) << " elements.\n";
return 0;
}myvector has 10 elements.