std::iterator_traits<std::common_iterator>

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Iterator library

Iterator concepts
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) is-integer-like is-signed-integer-like (C++20)(C++20)	sentinel_for (C++20) sized_sentinel_for (C++20) input_iterator (C++20) output_iterator (C++20) input_or_output_iterator (C++20)	forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
Iterator primitives
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++23)(C++20)(C++20)	iterator (deprecated in C++17) iterator_traits incrementable_traits (C++20) indirectly_readable_traits (C++20)
Algorithm concepts and utilities
Indirect callable concepts
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)	indirect_unary_predicate (C++20) indirect_binary_predicate (C++20)	indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
Common algorithm requirements
indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20)	indirectly_copyable_storable (C++20)   indirectly_swappable (C++20) indirectly_comparable (C++20)	permutable (C++20) mergeable (C++20) sortable (C++20)
Utilities
indirect_result_t (C++20)	projected (C++20)	projected_value_t (C++26)
Iterator adaptors
reverse_iterator make_reverse_iterator (C++14) move_iterator (C++11) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20)	front_insert_iterator back_insert_iterator inserter insert_iterator front_inserter back_inserter move_sentinel (C++20)	common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) make_const_iterator (C++23) make_const_sentinel (C++23)
Stream iterators istream_iterator    ostream_iterator istreambuf_iterator ostreambuf_iterator	Iterator customization points ranges::iter_move (C++20) ranges::iter_swap (C++20)
Iterator operations advance distance prev (C++11)   next (C++11) ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)	Range access begincbegin (C++11)(C++14) rbegincrbegin (C++14)(C++14)   endcend (C++11)(C++14) rendcrend (C++14)(C++14)   sizessize (C++17)(C++20) empty (C++17) data (C++17)

 

std::common_iterator

Member functions

common_iterator::common_iterator

common_iterator::operator=

common_iterator::operator*common_iterator::operator->

common_iterator::operator++common_iterator::operator++(int)

Non-member functions

operator== (C++20)

operator- (C++20)

iter_move (C++20)

iter_swap (C++20)

Helper classes

incrementable_traits<std::common_iterator> (C++20)

iterator_traits<std::common_iterator> (C++20)

 

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 const std::common_iterator<I, S>). void otherwise.
reference	std::iter_reference_t<I>

Example

Run this code

#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

See also

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)