C++

Reference

<iterator>

reverse_iterator

function template
<iterator>

std::operator- (reverse_iterator)

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(); }
Subtraction operator
Returns the distance between lhs and rhs.

The function returns the same as subtracting lhs's base iterator from rhs's base iterator.

Parameters

lhs, rhs
reverse_iterator objects (to the left- and right-hand side of the operator, respectively), having both the same template parameter (Iterator).
reverse_iterator objectss (to the left- and right-hand side of the operator, respectively) for whose base iterators the subtraction operation is defined.

Return value

The number of elements between lhs and rhs.

Example

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
 
// 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;
}

Output:

myvector has 10 elements.


Data races

Both objects, lhs and rhs, are accessed.

Exception safety

Provides the same level of guarantee as the reflexive operation applied on the base iterators of lhs and rhs.

See also

operator+ (reverse_iterator)
Addition operator (function template)
reverse_iterator::operator-
Subtraction operator (public member function)
reverse_iterator::operator-=
Retrocede iterator (public member function)