operator-(std::common_iterator)
From cppreference.com
< cpp | iterator | common iterator
template< std::sized_sentinel_for<I> I2, std::sized_sentinel_for<I> S2 > requires std::sized_sentinel_for<S, I2> |
(since C++20) | |
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.
Contents |
[edit] Parameters
x, y | - | iterator adaptors to compute the difference of |
[edit] Return value
- 0 if x.var holds an
S
object and y.var holds anS2
object, i.e. both of them hold a sentinel. - Otherwise, alt_x - alt_y, where
alt_x
andalt_y
are the alternatives held by x.var and y.var, respectively (either two iterators or one iterator and one sentinel).
[edit] Example
Run this code
#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'; }
Output:
0 -1 -2
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
LWG 3574 | C++20 | variant was fully constexpr (P2231R1) but common_iterator was not
|
also made constexpr |
[edit] See also
(C++20) |
advances the iterator adaptor (public member function) |