std::iterator_traits<std::common_iterator>

Defined in header `<iterator>`
template< std::input_iterator I, class S > struct iterator_traits<std::common_iterator<I, S>>;		(since C++20)

Provides the uniform interface to the properties of the std::common_iterator type.

Member types

Type name	Definition
`iterator_concept`	`std::forward_iterator_tag`, if `I` models `std::forward_iterator`. `std::input_iterator_tag` otherwise.
`iterator_category` (conditionally present)	Not defined, if std::iter_difference_t<I> is not an integral type. `std::forward_iterator_tag` otherwise, if std::iterator_traits<I>::iterator_category is valid and denotes a type that models `std::derived_from<std::forward_iterator_tag>`. `std::input_iterator_tag` otherwise.
`value_type`	std::iter_value_t<I>
`difference_type`	std::iter_difference_t<I>
`pointer`	decltype(c.operator->()), if it is well-formed (where `c` is an lvalue of type conststd::common_iterator<I,S>). void otherwise.
`reference`	std::iter_reference_t<I>

Example

#include <iterator>
#include <type_traits>
#include <vector>

int main()
{
    std::vector v{1, 2, 3, 4};
    using CV = std::common_iterator<
                    std::counted_iterator<std::vector<int>::iterator>,
                    std::default_sentinel_t>;
    CV i{std::counted_iterator{v.begin(), 3}};
    using TRCV = std::iterator_traits<decltype(i)>;
    static_assert(std::is_same<TRCV::iterator_concept, std::forward_iterator_tag>());
    static_assert(std::is_same<TRCV::iterator_category, std::forward_iterator_tag>());
    static_assert(std::is_same<TRCV::value_type, int>());
    static_assert(std::is_same<TRCV::difference_type,
                  std::vector<int>::difference_type>());
    static_assert(std::is_same<TRCV::pointer, decltype(i.operator->())>());
    static_assert(std::is_same<TRCV::reference, int&>());

    CV s{std::default_sentinel};
    using TRCS = std::iterator_traits<decltype(s)>;
    static_assert(std::is_same<TRCS::iterator_concept, std::forward_iterator_tag>());
    static_assert(std::is_same<TRCS::iterator_category, std::forward_iterator_tag>());
    static_assert(std::is_same<TRCS::value_type, int>());
    static_assert(std::is_same<TRCS::difference_type,
                  std::vector<int>::difference_type>());
    static_assert(std::is_same<TRCS::pointer, decltype(s.operator->())>());
    static_assert(std::is_same<TRCS::reference, int&>());
}

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
LWG 3749	C++20	if std::iter_difference_t<I> is not an integer type, `iterator_category` was `std::input_iterator_tag`	`iterator_category` is undefined in this case

iterator_traits	provides uniform interface to the properties of an iterator (class template)
std::incrementable_traits<std::common_iterator> (C++20)	computes the associated difference type of the `std::common_iterator` type (class template specialization)

std::iterator_traits<std::common_iterator>

Member types

Example

Defect reports

See also