Review Videos! • clocks, clock_cast, leap_seconds (https://youtu.be/WX3OmVu4lAs) • time_zone and time_zone_link (https://youtu.be/MODhhr7m-5s) • system_clock::now(), file_clock, leap second awareness (https://youtu Plus, the types often end up boiling down to constants anyway!18 Part III: Clocks19 What is a clock? #include #include using namespace std::chrono; class MyClock { public: is_steady = false; static time_point now() {} }; static_assert(is_clock_v); For a type T to qualify as a Clock, it must satisfy each of the following conditions: • The following qualified-ids

in :  std::system_clock: wall clock time from system-wide real-time clock  std::steady_clock: guarantees it never goes backwards  std::high_resolution_clock: has shortest possible tick C++20 adds:  utc_clock, tai_clock, gps_clock, and file_clock  Every clock has a now() method21 Clocks – Examples  Example: // Get current time as a time_point. system_clock::time_point tpoint tpoint { system_clock::now() }; // Or: auto tpoint { system_clock::now() }; // Convert to a time_t. time_t tt { system_clock::to_time_t(tpoint) }; // Convert to local time. tm* t { localtime(&tt) }; // Write

(int i { startValue }; i < startValue + numberOfValues; ++i) { time_t t { system_clock::to_time_t(system_clock::now()) }; cout << std::ctime(&t); co_yield i; } } int main() { auto gen 1 week into days62 Calendars & Timezones  New clocks (besides system_clock, steady_clock, high_resolution_clock):  utc_clock: represents Coordinated Universal Time (UTC), measures time since 00:00:00 00:00:00 UTC, Thursday, 1 January 1970, including leap seconds  tai_clock: represents International Atomic Time (TAI), measures time since 00:00:00, 1 January 1958, and was offseted 10 seconds ahead of

时间点类型： chrono::steady_clock::time_point 等 • 时间段类型： chrono::milliseconds ， chrono::seconds ， chrono::minutes 等 • 方便的运算符重载：时间点 + 时间段 = 时间点，时间点 - 时间点 = 时间段 • auto t0 = chrono::steady_clock::now();