std::chrono::month_day::month_day (3) Linux Manual Page

std::chrono::month_day::month_day – std::chrono::month_day::month_day

Synopsis

month_day() = default;
(1)(since C++ 20)

    constexpr month_day(const std::chrono::month &m, const std::chrono::day &d) noexcept;
(2)(since C++ 20)

Constructs a month_day.
1) Default constructor leaves the stored month and day values uninitialized.
2) Constructs a month_day that stores the month m and the day d.

Notes

A more convenient way to construct a month_day is with operator/, e.g., std::chrono::April/1.

See also

operator/ conventional syntax for Gregorian calendar date creation
          (function)
(C++20)