std::common_iterator

 

C++

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Feature test macros (C++20)

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Iterators library

Ranges library (C++20)

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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_or_output_iterator I, std::sentinel_for<I> S >     requires ( !std::same_as<I, S> && std::copyable<I> ) class common_iterator;		(since C++20)

std::common_iterator is an iterator I / sentinel S adaptor that may represent a non-common range (where the types of I and S differ) as a common_range, by containing either an iterator or a sentinel, and defining the appropriate equality comparison operators operator==.

std::common_iterator can be used as a "bridge" between sequences represented by iterator/sentinel pair and legacy functions that expect common_range-like sequences.

Data members

Member name	Definition
var	an object of type std::variant<I, S> (exposition-only member object*)

Member functions

(constructor) (C++20)	constructs a new iterator adaptor (public member function)
operator= (C++20)	assigns another iterator adaptor (public member function)
operator*operator-> (C++20)	accesses the pointed-to element (public member function)
operator++operator++(int) (C++20)	advances the iterator adaptor (public member function)

Non-member functions

operator== (C++20)	compares the underlying iterators or sentinels (function template)
operator- (C++20)	computes the distance between two iterator adaptors (function template)
iter_move (C++20)	casts the result of dereferencing the underlying iterator to its associated rvalue reference type (function)
iter_swap (C++20)	swaps the objects pointed to by two underlying iterators (function template)

Helper classes

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> (C++20)	provides uniform interface to the properties of the std::common_iterator type (class template specialization)

Example

Run this code

#include <algorithm>
#include <iostream>
#include <iterator>
#include <list>
#include <string>
 
template<class ForwardIter>
void fire(ForwardIter first, ForwardIter last)
{
    std::copy(first, last, std::ostream_iterator<std::string>{std::cout, " "});    
}
 
int main()
{
    std::list<std::string> stars{"Pollux", "Arcturus", "Mira", "Aldebaran", "Sun"};
 
    using IT = std::common_iterator<
                   std::counted_iterator<std::list<std::string>::iterator>,
                   std::default_sentinel_t>;
 
    fire(IT(std::counted_iterator(stars.begin(), stars.size() - 1)),
         IT(std::default_sentinel));
}

Output:

Pollux Arcturus Mira Aldebaran

References

• C++23 standard (ISO/IEC 14882:2024):

• 23.5.5 Common iterators [iterators.common]

• C++20 standard (ISO/IEC 14882:2020):

• 23.5.4 Common iterators [iterators.common]

See also

ranges::common_range (C++20)	specifies that a range has identical iterator and sentinel types (concept)
ranges::common_viewviews::common (C++20)	converts a view into a common_range (class template) (range adaptor object)