Defined in header
sentinel_for concept specifies the relationship between an
input_or_output_iterator type and a
semiregular type whose values denote a range. The exposition-only concept
__WeaklyEqualityComparableWith is described in
 Semantic requirements
i be values of type
I, respectively, such that
) denotes a range.
sentinel_for<S, I> is modeled only if:
- i == s is well-defined.
- If bool(i != s) then
iis dereferenceable and
)denotes a range.
- std::assignable_from<I&, S> is either modeled or not satisfied.
The domain of
== can change over time. Given an iterator
i and sentinel
s such that
) denotes a range and i != s,
) is not required to continue to denote a range after incrementing any iterator equal to
i (and so i == s is no longer required to be well-defined after such an increment).
A sentinel type and its corresponding iterator type are not required to model
equality_comparable_with, because the sentinel type may not be comparable with itself, and they are not required to have a common reference type.
It has been permitted to use a sentinel type different from the iterator type in the range-based
for loop since C++17.
 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 3453||C++20||semantic requirements for