# std::ranges::transform_view<V,F>::iterator<Const>::base

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< cpp‎ | ranges‎ | transform view‎ | iterator

constexpr const ranges::iterator_t<Base>& base() const & noexcept; | (1) | (since C++20)
constexpr ranges::iterator_t<Base> base() &&; | (2) | (since C++20)

Returns the underlying iterator.

1) Returns a reference to the underlying iterator.
2) Move constructs the result from the underlying iterator.

### Parameters

(none)

### Return value

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

### Example

Run this code

    #include <algorithm>
    #include <iostream>
    #include <iterator>
    #include <ranges>

    int main()
    {
        const auto v = { 0, 1, 2, 3, 4 };
        auto x2 = [](int x) { return x << 1; };
        std::ranges::transform_view tv{ v, x2 };
        std::ostream_iterator<int> ostr{ std::cout, " " };

        std::ranges::copy(v, ostr), std::cout << '\n';
        std::ranges::copy(tv.base(), ostr), std::cout << '\n';
        std::ranges::copy(tv, ostr), std::cout << '\n';
    }

Output:

    0 1 2 3 4
    0 1 2 3 4
    0 2 4 6 8

### 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 3533 | C++20 | the const& overload of `base` returns a copy of the underlying iterator | returns a reference
LWG 3593 | C++20 | the const& overload of `base` might not be noexcept | made noexcept

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