std::chrono::year_month::year_month
From cppreference.com
                    
                                        
                    < cpp | chrono | year month
                    
                                                            
                    | 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
| (C++20) | conventional syntax for Gregorian calendar date creation (function) |