std::iterator_traitsstd::counted_iterator - cppreference.com (original) (raw)

Inherits the properties from customized (generated from either a standard partial specialization or a program-defined specialization) std::iterator_traits<I>, with the member type pointer adjusted, where I models input_iterator.

Notably, the iterator_concept (if present) and iterator_category are inherited from std::iterator_traits<I>.

The condition in the requires-clause is true if and only if std::iterator_traits<I> is not generated from the primary template.

[edit] Note

Before P2259R1, this specialization is used even if std::iterator_traits<I> is generated from the primary template. As a result, when testing std::counted_iterator<I> against an iterator concept (e.g. forward_iterator), the determination of /*ITER_CONCEPT*/ does not take I::iterator_concept into account, and thus std::counted_iterator<I> sometimes erroneously behaves as if it cannot model that concept. This incorrect behavior is implemented in libstdc++ prior to 10.4, and in MSVC STL prior to VS 2022 17.0 Preview 3.

The standard library provides partial specializations of std::iterator_traits for pointer types, std::counted_iterator, and std::common_iterator.

[edit] Example

#include #include #include #include   int main() { std::vector v{1, 2, 3, 4}; std::list l{1, 2, 3, 4}; std::counted_iterator iv{v.begin(), 3}; std::counted_iterator il{l.begin(), 3}; static_assert(std::is_same<int*, std::iterator_traits<decltype(iv)>::pointer>()); static_assert(std::is_same<void, std::iterator_traits<decltype(il)>::pointer>()); }

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also

| | provides uniform interface to the properties of an iterator (class template) | | ------------------------------------------------------------------------------- |