gps_clock class

A clock for Global Positioning System (GPS) time.

Syntax

class gps_clock; // C++20

Remarks

This clock measures time since Sunday, 6 January 1980 00:00:00 UTC.

This clock doesn't account for leap seconds. Whenever a leap second is added into UTC time, UTC falls another second behind GPS time.

GPS time is behind TAI time by 19 seconds because 10 seconds were added to TAI time in 1972 to account for the leap seconds that had accumulated to that point, and 9 more leap seconds were added to TAI time between 1970 and 1980.

Members

Name	Description
from_utc	Static. Converts a utc_time to a gps_time.
now	Static. Returns the GPS current time.
to_utc	Static. Converts a gps_time to a utc_time.

Non-members

Name	Description
from_stream	Parse a gps_time from the given stream using the specified format.
operator<<	Output a gps_time to the given stream.

Convenience type aliases

Name	Description
gps_clock::duration	In Microsoft's implementation, it's a synonym for duration<long long, ratio<1, 10'000'000>. It represents a duration of time, as measured in units of 100 nanoseconds.
gps_clock::period	In Microsoft's implementation, it's a synonym for ratio<1, 10'000'000>. It represents the time in fractions of a second (100 nanoseconds) between each clock tick in the duration.
gps_clock::rep	A synonym for the type (long long) used to represent the integral units in this clock's gps_clock::duration.
gps_clock::time_point	A synonym for time_point<gps_clock>. Used to represent a time_point for this clock.

Related

Name	Description
gps_time	A synonym for template <class Duration> using gps_time = time_point<gps_clock, Duration>. Used to represent a time_point for a gps_clock. You specify the Duration. Defined in std::chrono
gps_seconds	A synonym for using gps_seconds = gps_time<seconds>; A count of seconds, represented by a time_point that is associated with a gps_clock. Defined in std::chrono

Public Constants

Name	Description
gps_clock::is_steady constant	Indicates whether the clock type is steady. Its value is false.

Requirements

Header: <chrono> (since C++20)

Namespace: std::chrono

Compiler Option: /std:c++latest

from_utc

Static method that converts a utc_time to a gps_time.

template<class Duration>
static gps_time<common_type_t<Duration, seconds>>
from_utc(const utc_time<Duration>& t) noexcept;

Parameters

t
The utc_time to convert.

Return value

A gps_time set to the same point in time as the utc_time t. It's computed as gps_time<common_type_t<Duration, seconds>>{t.time_since_epoch()} - 315964809s where 315964809s == sys_days{1980y/January/Sunday[1]} - sys_days{1970y/January/1} + 9s. Which is the number of seconds between the utc_clock epoch and the gps_clock epoch.

to_utc

Static method that converts a gps_time to a utc_time.

template<class Duration>
static utc_time<common_type_t<Duration, seconds>>
to_utc(const gps_time<Duration>& t) noexcept;

Parameters

t
The gps_time to convert.

Return Value

A utc_time set to the same point in time as the gps_time. It's computed as gps_time<common_type_t<Duration, seconds>>{t.time_since_epoch()} + 315964809s where 315964809s == sys_days{1980y/January/Sunday[1]} - sys_days{1970y/January/1} + 9s. That's the number of seconds between the epochs of the utc_clock and the gps_clock.

is_steady

Static value that specifies whether the clock type is steady. In Microsoft's implementation, is_steady_constant is always false. Because the gps_clock isn't steady, you can't reliably use this clock to take the time before an event, the time after an event, and subtract them to get the duration of the event because the clock may be adjusted during that time.

static const bool is_steady = system_clock::is_steady; // system_clock::is_steady equals false

now

Static method that returns the current GPS time.

static time_point now() noexcept;

Return Value

A time_point object that represents the current time. The returned time point is effectively from_utc(utc_clock::now()).

See also

<chrono>
file_clock class
high_resolution_clock
local_t struct
steady_clock struct
system_clock struct
tai_clock class
Header Files Reference