# std::chrono::time_zone::to_sys

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< cpp‎ | chrono‎ | time zone

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_point`s, those two `time_point`s 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.

### Exceptions

1) Throws:

- std::chrono::ambiguous_local_time if the conversion is ambiguous,
- std::chrono::nonexistent_local_time if `tp` represents a nonexistent time.

### Notes

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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