template< class Duration >
auto to_sys(const std::chrono::local_time<Duration>& tp) const
    -> std::chrono::sys_time<std::common_type_t<Duration, std::chrono::seconds>>;
(since C++20)
template< class Duration >
auto to_sys(const std::chrono::local_time<Duration>& tp, std::chrono::choose z) const
    -> std::chrono::sys_time<std::common_type_t<Duration, std::chrono::seconds>>;
(since C++20)

Converts the local_time tp in this time zone to the corresponding sys_time.

1) Throws an exception if the conversion is ambiguous or if tp represents a nonexistent time.
2) Resolves ambiguity according to the value of z:
  • If z == std::chrono::choose::earliest, returns the earlier sys_time.
  • If z == std::chrono::choose::latest, returns the later sys_time
If tp represents a nonexistent time between two UTC time_points, those two time_points will be the same, and that time_point will be returned.

Return value

The UTC equivalent of tp according to the rules of this time zone.


1) Throws a std::chrono::ambiguous_local_time if the conversion is ambiguous. Throws a std::chrono::nonexistent_local_time if tp represents a nonexistent time.


The precision of the result is at least std::chrono::seconds, and will be finer if the argument has finer precision.

Ambiguous and nonexistent local times can occur as a result of time zone transitions (such as daylight saving time). For example, "2016-03-13 02:30:00" does not exist in the "America/New_York" time zone, while "2016-11-06 01:30:00" in that time zone can correspond to two UTC time points: 2016-11-06 05:30:00 UTC and 2016-11-06 06:30:00 UTC.

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