25 Time library [time]

25.7 Clocks [time.clock]

25.7.4 Class gps_­clock [time.clock.gps]

25.7.4.1 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 falls another second behind 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
:
noexcept(from_­utc(utc_­clock::now())) is false.
end note
]