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The latest version of this topic can be found at system_clock Structure.
Represents a clock type that is based on the real-time clock of the system.
Syntax
struct system_clock;
Remarks
A clock type is used to obtain the current time as UTC. The type embodies an instantiation of duration and the class template time_point, and defines a static member function now() that returns the time.
A clock is monotonic if the value that is returned by a first call to now() is always less than or equal to the value that is returned by a subsequent call to now().
A clock is steady if it is monotonic and if the time between clock ticks is constant.
In this implementation, a system_clock is synonymous with a high_resolution_clock.
Members
Public Typedefs
| Name | Description |
|---|---|
system_clock::duration |
A synonym for duration<rep, period>. |
system_clock::period |
A synonym for the type that is used to represent the tick period in the contained instantiation of duration. |
system_clock::rep |
A synonym for the type that is used to represent the number of clock ticks in the contained instantiation of duration. |
system_clock::time_point |
A synonym for time_point<Clock, duration>, where Clock is a synonym for either the clock type itself or another clock type that is based on the same epoch and has the same nested duration type. |
Public Methods
| Name | Description |
|---|---|
| system_clock::from_time_t Method | Static. Returns a time_point that most closely approximates a specified time. |
| system_clock::now Method | Static. Returns the current time. |
| system_clock::to_time_t Method | Static. Returns a time_t object that most closely approximates a specified time_point. |
Public Constants
| Name | Description |
|---|---|
| system_clock::is_monotonic Constant | Specifies whether the clock type is monotonic. |
| system_clock::is_steady Constant | Specifies whether the clock type is steady. |
Requirements
Header: chrono
Namespace: std::chrono
system_clock::from_time_t Method
Static method that returns a time_point that most closely approximates the time that is represented by Tm.
static time_point from_time_t(time_t Tm) noexcept;
Parameters
Tm
A time_t object.
system_clock::is_monotonic Constant
Static value that specifies whether the clock type is monotonic.
static const bool is_monotonic = false;
Return Value
In this implementation, system_clock::is_monotonic always returns false.
Remarks
A clock is monotonic if the value that is returned by a first call to now() is always less than or equal to the value that is returned by a subsequent call to now().
system_clock::is_steady Constant
Static value that specifies whether the clock type is steady.
static const bool is_steady = false;
Return Value
In this implementation, system_clock::is_steady always returns false.
Remarks
A clock is steady if it is monotonic and if the time between clock ticks is constant.
system_clock::now Method
Static method that returns the current time.
static time_point now() noexcept;
Return Value
A time_point object that represents the current time.
system_clock::to_time_t Method
Static method that returns a time_t that most closely approximates the time that is represented by Time.
static time_t to_time_t(const time_point& Time) noexcept;
Parameters
Time
A time_point object.