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std::iterator_traits(3) C++ Standard Libary std::iterator_traits(3) NAME std::iterator_traits - std::iterator_traits Synopsis Defined in header <iterator> template< std::input_iterator I > requires /* see below */ struct iterator_traits<std::counted_iterator<I>> : std::iterator_traits<I> { (since C++20) using pointer = std::conditional_t<std::contiguous_iterator<I>, std::add_pointer_t<std::iter_reference_t<I>>, void>; }; Inherits the properties from customized (generated from either a standard partial specialization or a program-defined specialization) std::itera- tor_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::it- erator_traits<I> is not generated from the primary template. Note Before P2259R1, this specialization is used even if std::itera- tor_traits<I> is generated from the primary template. As a result, when testing std::counted_iterator<I> against an iterator concept (e.g. for- ward_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 lib- stdc++ prior to 10.4, and in MSVC STL prior to VS 2022 17.0 Preview 3. The standard library provides partial specializations of std::itera- tor_traits for pointer types, std::counted_iterator, and std::common_iterator. Example // Run this code #include <iterator> #include <type_traits> #include <list> #include <vector> 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<de- cltype(iv)>::pointer>()); static_assert(std::is_same<void, std::iterator_traits<de- cltype(il)>::pointer>()); } Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Cor- rect behavior P2259R1 C++20 there's no requires-clause con- straint added pointer is unconditionally defined as void See also iterator_traits provides uniform interface to the properties of an iterator (class template) http://cppreference.com 2022.07.31 std::iterator_traits(3)
NAME | Synopsis | Note | Example | See also
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