NAME¶

std::sentinel_for - std::sentinel_for

Synopsis¶

Defined in header <iterator>
template<class S, class I>

concept sentinel_for =
std::semiregular<S> && (since C++20)
std::input_or_output_iterator<I> &&

__WeaklyEqualityComparableWith<S, I>;

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> is modeled only if:

* i == s is well-defined.
* If bool(i != s) then i is dereferenceable and [++i, s) 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
[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 is no longer
required to be well-defined after such an increment).

Notes¶

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 sentinel_for were too strengthened
loose for ranges::advance