[time.clock.gps] (original) (raw)

30 Time library [time]

30.7 Clocks [time.clock]

30.7.5 Class gps_clock [time.clock.gps]

30.7.5.1 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 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 Cpp17TrivialClockunless the implementation can guarantee thatgps_clock​::​now() does not propagate an exception.

[Note 1:

noexcept(from_utc(utc_clock​::​now())) is false.

— _end note_]

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

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_]

30.7.5.3 Non-member functions [time.clock.gps.nonmembers]

template<class charT, class traits, class Duration> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const gps_time<Duration>& t);

Effects: Equivalent to:return os << format(os.getloc(), _STATICALLY-WIDEN_<charT>("{:L%F %T}"), t);

[Example 1: auto st = sys_days{2000y/January/1};auto gt = clock_cast<gps_clock>(st); cout << format("{0:%F %T %Z} == {1:%F %T %Z}\n", st, gt);

Produces this output:

2000-01-01 00:00:00 UTC == 2000-01-01 00:00:13 GPS

— _end example_]

template<class charT, class traits, class Duration, class Alloc = allocator<charT>> basic_istream<charT, traits>& from_stream(basic_istream<charT, traits>& is, const charT* fmt, gps_time<Duration>& tp, basic_string<charT, traits, Alloc>* abbrev = nullptr, minutes* offset = nullptr);

Effects: Attempts to parse the input stream isinto the gps_time tp using the format flags given in the NTCTS fmtas specified in [time.parse].

If the parse fails to decode a valid date,is.setstate(ios_base​::​failbit) is called andtp is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Additionally, the parsed offset will be subtracted from the successfully parsed timestamp prior to assigning that difference to tp.