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

std::chrono::year_month::year_month – std::chrono::year_month::year_month

Synopsis

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

    constexpr year_month(const std::chrono::year &y, const std::chrono::month &m) noexcept;
(2)(since C++ 20)

Constructs a year_month object.
1) Default constructor leaves the year and month uninitialized.
2) Constructs a year_month object storing the year y and the month m.

Notes

A more convenient way to construct a year_month is with operator/, e.g., 2007y/std::chrono::April.

See also

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