std::chrono::system_clock - cppreference.com (original) (raw)
std::chrono::system_clock
| | | | | -------------------- | | ------------- | | class system_clock; | | (since C++11) |
Class std::chrono::system_clock represents the system-wide real time wall clock.
It may not be monotonic: on most systems, the system time can be adjusted at any moment. It is the only C++ clock that has the ability to map its time points to C-style time.
std::chrono::system_clock meets the requirements of TrivialClock.
| The epoch of system_clock is unspecified, but most implementations use Unix Time (i.e., time since 00:00:00 Coordinated Universal Time (UTC), Thursday, 1 January 1970, not counting leap seconds). | (until C++20) |
|---|---|
| system_clock measures Unix Time (i.e., time since 00:00:00 Coordinated Universal Time (UTC), Thursday, 1 January 1970, not counting leap seconds). | (since C++20) |
Contents
Time point family
| Defined in namespace std::chrono | | | | ---------------------------------------------------------------------------------------------------------------------------------- | | ------------- | | template<class Duration> using sys_time = std::chrono::time_point<std::chrono::system_clock, Duration>; | | (since C++20) | | using sys_seconds = sys_time<std::chrono::seconds>; | | (since C++20) | | using sys_days = sys_time<std::chrono::days>; | | (since C++20) |
[edit] Member types
| Member type | Definition |
|---|---|
| rep | signed arithmetic type representing the number of ticks in the clock's duration |
| period | a std::ratio type representing the tick period of the clock, in seconds |
| duration | std::chrono::duration<rep, period>, capable of representing negative durations |
| time_point | std::chrono::time_pointstd::chrono::system\_clock\ |
[edit] Member constants
| constexpr bool is_steady[static] | true if the time between ticks is always constant, i.e. calls to now() return values that increase monotonically even in case of some external clock adjustment, otherwise false (public static member constant) |
|---|
[edit] Member functions
[edit] Notes
The system_clock's time value can be internally adjusted at any time by the operating system, for example due to NTP synchronization or the user changing the system's clock. Daylight Saving Time and time zone changes, however, do not affect it since it is based on the UTC time-zone.