operator-(std::counted_iterator)

Computes the distance between two iterator adaptors.

The behavior is undefined if x and y do not point to elements of the same sequence. That is, there must exist some n such that std::next (x.base ( ), x.count ( ) + n) and std::next (y.base ( ), y.count ( ) + n)

This function template is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup

Parameters

Return value

y.count() - x.count()

Notes

Since the length counts down, not up, the order of the arguments of operator- in the underlying expression is reversed, i.e. y is lhs and x is rhs

Example

#include <initializer_list>
#include <iterator>
 
int main()
{
    static constexpr auto v = {1, 2, 3, 4, 5, 6};
    constexpr std::counted_iterator<std::initializer_list<int>::iterator>
        it1{v.begin(), 5},
        it2{it1 + 3},
        it3{v.begin(), 2};
 
    static_assert(it1 - it2 == -3);
    static_assert(it2 - it1 == +3);
//  static_assert(it1 - it3 == -3); // UB: operands of operator- do not refer to
                                    // elements of the same sequence
}

See also