now() method21 Clocks – Examples  Example: // Get current time as a time_point. system_clock::time_point tpoint { system_clock::now() }; // Or: auto tpoint { system_clock::now() }; // Convert to a time_t Time Points  std::time_point in  Associated with a clock  Represents point in time as duration relative to epoch (= origin of clock)  Support arithmetic (tp = time_point, d = duration) d tp += d tp -= d25 Time Points  Example: // Create a time_point representing the epoch of the // associated steady clock. time_point tp1; // Add 10 minutes to the time_point. tp1 +=

granularity using duration = milliseconds; using time_point = time_point; static constexpr bool is_steady = false; static time_point now() {} }; static_assert(is_clock_v); following qualified-ids must be valid and denote a type • T::rep • T::period • T::duration • T::time_point • The following expressions must be well- formed when treated as an unevaluated operand • T::is_steady file_clock Unspecified Typically: Jan 1, 1970 on POSIX; Jan 1, 1601 on Windows Used to create the time_point system used for file_time_type Unspecified * Coordinated Universal Time (UTC) or Greenwich Mean

std::filesystem::file_time_type, epoch is unspecified63 Calendars & Timezones  New type alias sys_time: a time_point of a system_clock with certain duration  Additionally:  using sys_seconds = sys_time; Example: system_clock::time_point t { sys_days { 2020y / September / 15d } }; // date -> time_point auto yearmonthday { year_month_day { floor(t) } }; // time_point -> date64 Calendars

TYPES TESTING WITH EVEN MORE TYPES using namespace std::chrono_literals; using T = std::chrono::time_point; std::vector TYPES TESTING WITH EVEN MORE TYPES using namespace std::chrono_literals; using T = std::chrono::time_point; std::vector main.cpp:16:28: error: no matching conversion for static_cast from 'const long' to 'std::chrono::time_point > >' const auto

query() noexcept; const Query& query() const noexcept; void abort(); typename WaitableTimer::time_point last_write() const noexcept; bool start_write() noexcept; void complete_write(); 28 bool

Create separate types for point and delta quantities – E.g., std::chrono has separate types for time_point (point) and duration (delta). ■ Typically, only deltas will benefit from UDLs. When defining

Amir Kirsh @ CppCon, 2024 Supporting Generic Ordersclass TimedOrder { std::vectortime_point, Price> price_limits; Quantity quantity; public: // [ctor] Price getPrice() const

单位。 • 时间点例子： 2022 年 1 月 8 日 13 点 07 分 10 秒 • 时间段例子： 1 分 30 秒 • 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 =