std::common_iterator - cppreference.com

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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

Non-member functions

	compares the underlying iterators or sentinels (function template) [edit]
	computes the distance between two iterator adaptors (function template) [edit]
	casts the result of dereferencing the underlying iterator to its associated rvalue reference type (function) [edit]
	swaps the objects pointed to by two underlying iterators (function template) [edit]

Helper classes

Example

#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]