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std::counted_iterator<I>::base - cppreference.com

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constexpr const I& base() const& noexcept;

 (1) (since C++20)

constexpr I base() &&;

 (2) (since C++20)

Returns the underlying base iterator.

1) Returns a reference to the underlying iterator.

2) Move constructs the return value from the underlying iterator.

Parameters

(none)

Return value

1) A reference to the underlying iterator.

2) An iterator move constructed from the underlying iterator.

Exceptions

May throw implementation-defined exceptions.

Example

#include <algorithm>
#include <iostream>
#include <iterator>
#include <type_traits>
#include <vector>

int main()
{
    std::vector<int> v{0, 1, 2, 3, 4};

    std::reverse_iterator<std::vector<int>::iterator> reverse{v.rbegin()};

    std::counted_iterator counted{reverse, 3};

    static_assert(std::is_same<
        decltype(counted.base()),
        std::reverse_iterator<std::vector<int>::iterator> const&
    >{});

    std::cout << "Print with reverse_iterator: ";
    for (auto r = counted.base(); r != v.rend(); ++r)
        std::cout << *r << ' ';
    std::cout << '\n';

    std::cout << "Print with counted_iterator: ";
    for (; counted != std::default_sentinel; ++counted)
        std::cout << counted[0] << ' ';
    std::cout << '\n';
}

Output: 

Print with reverse_iterator: 4 3 2 1 0
Print with counted_iterator: 4 3 2

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 3391 C++20 the const version of base returns a copy of the underlying iterator returns a reference
LWG 3593 C++20 the const version of base returns a reference but might not be noexcept made noexcept

See also