# std::counted_iterator<I>::counted_iterator

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< cpp‎ | iterator‎ | counted iterator

constexpr counted_iterator() requires std::default_initializable<I> = default; | (1) | (since C++20)
constexpr counted_iterator( I x, std::iter_difference_t<I> n ); | (2) | (since C++20)
template< class I2 > requires std::convertible_to<const I2&, I> constexpr counted_iterator( const counted_iterator<I2>& other ); | (3) | (since C++20)

Constructs a new iterator adaptor.

1) Default constructor. Value-initializes the underlying iterator and initialized the underlying length with ​0​. Operations on the resulting iterator have defined behavior if and only if the corresponding operations on a value-initialized `I` also have defined behavior.
2) The underlying iterator is initialized with std::move(x) and the underlying length is initialized with `n`. The behavior is undefined if `n` is negative.
3) The underlying iterator and length are initialized with those of `other`.

### Parameters

x | - | iterator to adapt
n | - | distance to the end
other | - | iterator adaptor to convert

### Example

Run this code

    #include <algorithm>
    #include <initializer_list>
    #include <iostream>
    #include <iterator>

    int main() {
        static constexpr auto pi = {3, 1, 4, 1, 5, 9, 2};

        // (1) default constructor:
        constexpr std::counted_iterator<std::initializer_list<int>::iterator> i1{};
        static_assert(i1 == std::default_sentinel);
        static_assert(i1.count() == 0);

        // (2) initializes the iterator and length respectively:
        constexpr std::counted_iterator<std::initializer_list<int>::iterator> i2{
            pi.begin(), pi.size() - 2
        };
        static_assert(i2.count() == 5);
        static_assert(*i2 == 3 && i2[1] == 1);

        // (3) converting-constructor:
        std::counted_iterator<std::initializer_list<const int>::iterator> i3{i2};

        std::ranges::copy(i3, std::default_sentinel,
            std::ostream_iterator<const int>{std::cout, " "});
    }

Output:

    3 1 4 1 5

### See also

operator= (C++20) | assigns another iterator adaptor (public member function)

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