operator-(std::counted_iterator) - cppreference.com (original) (raw)
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) refer to the same element.
This function template is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::counted_iterator is an associated class of the arguments.
[edit] Parameters
| x, y | - | iterator adaptors to compute the difference of |
|---|
[edit] Return value
y.count() - x.count()
[edit] 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.
[edit] Example
#include #include int main() { static constexpr auto v = {1, 2, 3, 4, 5, 6}; constexpr std::counted_iterator<std::initializer_list::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 }