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.



Return value

1) A reference to the underlying iterator.
1) An iterator move constructed from the underlying iterator.


May throw implementation-defined exceptions.


#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};
    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';


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

accesses the pointed-to element
(public member function)
returns the distance to the end
(public member function)

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