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std::sentinel_for

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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.

[edit] 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.

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).

[edit] Notes

A sentinel type and its corresponding iterator type are not required to model equality_comparable_with, because the sentinel type may be not 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.