std::chrono::system_clock

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< cpp‎ | chrono
 
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Date and time utilities
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system_clock
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chrono I/O
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C-style date and time
 
std::chrono::system_clock
 
Defined in header <chrono>
class system_clock;
 (since 哋它亢++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 哋它亢++ 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 哋它亢++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 哋它亢++20)

Time point family

Defined in namespace std::chrono
template<class Duration>
using sys_time = std::chrono::time_point<std::chrono::system_clock, Duration>;
 (since 哋它亢++20)
using sys_seconds = sys_time<std::chrono::seconds>;
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using sys_days = sys_time<std::chrono::days>;
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 performs stream output on a sys_time
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 parses a sys_time from a stream according to the provided format
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 formatting support for sys_time
(class template specialization)

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_point<std::chrono::system_clock>

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)

Member functions

[static]
 returns a std::chrono::time_point representing the current point in time
(public static member function)
[static]
 converts a system clock time point to std::time_t
(public static member function)
[static]
 converts std::time_t to a system clock time point
(public static member function)

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.

See also

(哋它亢++11)
 monotonic clock that will never be adjusted
(class)
(哋它亢++11)
 the clock with the shortest tick period available
(class)
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