25 Iterators library [iterators]

25.3 Iterator requirements [iterator.requirements]

25.3.4 Iterator concepts [iterator.concepts] Concept sentinel_for [iterator.concept.sentinel]

The sentinel_for concept specifies the relationship between an input_or_output_iterator type and a semiregular type whose values denote a range.
Let s and i be values of type S and I such that [i, s) denotes a range.
Types S and I model sentinel_for<S, I> only if
  • i == s is well-defined.
  • If bool(i != s) then i is dereferenceable and [++i, s) denotes a range.
  • assignable_from<I&, S> is either modeled or not satisfied.
The domain of == is not static.
Given an iterator i and sentinel s such that [i, s) denotes a range and i != s, i and s are not required to continue to denote a range after incrementing any other iterator equal to i.
Consequently, i == s is no longer required to be well-defined.