29 Time library [time]

29.7 Clocks [time.clock]

29.7.5 Class gps_clock [time.clock.gps] Overview [time.clock.gps.overview]

namespace std::chrono { class gps_clock { public: using rep = a signed arithmetic type; using period = ratio<unspecified, unspecified>; using duration = chrono::duration<rep, period>; using time_point = chrono::time_point<gps_clock>; static constexpr bool is_steady = unspecified; static time_point now(); template<class Duration> static utc_time<common_type_t<Duration, seconds>> to_utc(const gps_time<Duration>&) noexcept; template<class Duration> static gps_time<common_type_t<Duration, seconds>> from_utc(const utc_time<Duration>&) noexcept; }; }
The clock gps_clock measures seconds since the first Sunday of January, 1980 00:00:00 UTC.
Leap seconds are not inserted into GPS.
Therefore every time a leap second is inserted into UTC, UTC shifts another second with respect to GPS.
Aside from the offset from 1958y/January/1 to 1980y/January/Sunday[1], GPS is behind TAI by 19s due to the 10s offset between 1958 and 1970 and the additional 9 leap seconds inserted between 1970 and 1980.
gps_clock is not a Cpp17TrivialClock unless the implementation can guarantee that gps_clock​::​now() does not propagate an exception.
[Note 1: 
noexcept(from_utc(utc_clock​::​now())) is false.
— end note]