std::sentinel_for

Defined in header <iterator>
template < class S, class I > concept sentinel_for = std::semiregular <S> && std::input_or_output_iterator <I> &&         __WeaklyEqualityComparableWith<S, I> ;		(since C++20)

The 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 equality_comparable

Semantic requirements

Let s and i be values of type S and I, respectively, such that [i, s) denotes a range. sentinel_for<S, I>

• i == s is well-defined.
• If bool(i != s) then i is dereferenceable and [ ++i ,  s )
• std::assignable_from <I&, S>

The domain of == can change over time. Given an iterator i and sentinel s such that [ i ,  s ) denotes a range and i != s, [ i ,  s ) is not required to continue to denote a range after incrementing any iterator equal to i (and so i == s

Notes

A sentinel type and its corresponding iterator type are not required to model equality_comparable_with

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 sentinel_for were too loose for ranges::advance	strengthened