27 Time library [time]

27.7 Clocks [time.clock]

27.7.5 Class gps_­clock [time.clock.gps]

27.7.5.2 Member functions [time.clock.gps.members]

static time_point now();
Returns: from_­utc(utc_­clock​::​now()), or a more accurate value of gps_­time.
template<class Duration> static utc_time<common_type_t<Duration, seconds>> to_utc(const gps_time<Duration>& t) noexcept;
Returns: utc_time<common_type_t<Duration, seconds>>{t.time_since_epoch()} + 315964809s
[Note 1: 315964809s == sys_days{1980y/January/Sunday[1]} - sys_days{1970y/January/1} + 9s — end note]
template<class Duration> static gps_time<common_type_t<Duration, seconds>> from_utc(const utc_time<Duration>& t) noexcept;
Returns: gps_time<common_type_t<Duration, seconds>>{t.time_since_epoch()} - 315964809s
[Note 2: 315964809s == sys_days{1980y/January/Sunday[1]} - sys_days{1970y/January/1} + 9s — end note]