[Boost-users] convert separate year, month, day, hour, minute, secs, ms to milliseconds since epoch

I am using C++14 and boost 1.64.0 (could move to newest boost), and need to convert date and time pieces to a single value for milliseconds since the epoch. This is what I have: int64_t msSinceEpoch(int year,int month,int day,int hour,int minute,int second,int ms) { struct std::tm t; t.tm_sec = second; t.tm_min = minute; t.tm_hour = hour; t.tm_mday = day; t.tm_mon = month-1; t.tm_year = year-1900; t.tm_isdst = 0; return (1000* timegm(&t))+ms; // is timegm cross-platform? } Is there a better way? Could not figure out how to use boost::chrono :( Something else? Kind Regards, Vic