operator- (std::common_iterator)

Computes the distance between two iterator adaptors. Two sentinels are considered equal.

Let var denote the underlying std::variant member object in std::common_iterator , the behavior is undefined if either x or y is invalid, i.e. x. var . valueless_by_exception ( ) || y. var . valueless_by_exception ( ) is true .

This function template is not visible to ordinary unqualified or qualified lookup , and can only be found by argument-dependent lookup when std::common_iterator<I> is an associated class of the arguments.

Parameters

Return value

• ​ 0 ​ if x. var holds an S object and y. var holds an S2 object, i.e. both of them hold a sentinel.
• Otherwise, alt_x - alt_y , where alt_x and alt_y are the alternatives held by x. var and y. var , respectively (either two iterators or one iterator and one sentinel).

Example

#include <algorithm>
#include <iostream>
#include <iterator>
 
int main()
{
    int a[]{0, 1, 2, 3, 4, 5};
 
    using CI = std::common_iterator<
                   std::counted_iterator<int*>,
                   std::default_sentinel_t
                   >;
 
    CI i1{std::counted_iterator{a + 1, 2}};
    CI i2{std::counted_iterator{a, 3}};
    CI s1{std::default_sentinel};
    CI s2{std::default_sentinel};
 
    std::cout << (s2 - s1) << ' '
              << (i2 - i1) << ' '
              << (i1 - s1) << '\n';
}

0 -1 -2

Defect reports

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

See also