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Variants

std::chrono::year:: year

From cppreference.net
C++
Date and time library
std::chrono::year
year ( ) = default ;
(1) (since C++20)
constexpr explicit year ( int y ) noexcept ;
(2) (since C++20)

Constructs a year object.

1) Default constructor leaves the year value uninitialized.
2) If y is in the range [ - 32767 , 32767 ] , constructs a year object holding the year value y . Otherwise the value held is unspecified.

Example

Run this code 
#include <chrono>
#include <iostream>
int main()
{
    using namespace std::chrono;
    constexpr int leap_years = []
    {
        int count{};
        for (int i{year::min()}; i <= int{year::max()}; ++i)
            if (year{i}.is_leap()) // uses constructor (2)
                ++count;
        return count;
    } ();
    static_assert(15891 == leap_years);
    std::cout << "There are " << leap_years << " leap years in the range ["
              << int(year::min()) << ", " << int(year::max()) << "].\n";
}

Output: 

There are 15891 leap years in the range [-32767, 32767].