In the date library by Howard Hinnant that’s been added to the c++ standard library, the first I call current_zone(), which is the equivalent of std::chrono::current_zone() in C++20. It tries to get the get the tzdb_list, it is a static variable that’s lazily initialised:

I’ve calculated the day, day of month and year, and seconds, minutes, and hours using std::chrono::local_days, I just now need to get the day of the week. The code I’m using was given by Howard Hinnant on an answer here, comments are mine:

I found that code: