std::iterator_traits<std::counted_iterator>
Defined in header <iterator>
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template< std::input_iterator I > requires /* see below */ |
(since C++20) | |
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.
Contents |
[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 <iterator> #include <list> #include <type_traits> #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<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.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
P2259R1 | C++20 | there's no requires-clausepointer is unconditionally defined as void
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constraint added |
[edit] See also
provides uniform interface to the properties of an iterator (class template) |