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c++c++-chrono

To identify ambigious local time using std::chrono

How to identify the given epoch time converted to local time(time zone UTC-8) is a ambigious ?

Example. Epoch time 1699173796 when converted to local time(time zone UTC-8) gives November 5, 2023 1:43:16 AM and for the same local time one more epoch time also available 1699177396.

How to identify this time ambiguity using std::chrono or using any other c++ libraries.

And once find it is a ambigious time, how to select the earliest/latest time for that

I gone through the std::chrono libraries not able to find any APIs

Solution

  • First convert your sys_time into a local time:

    using namespace std::chrono;

auto zone = locate_zone("America/Los_Angeles");
sys_seconds tp(1699173796s);
auto local = zone->to_local(tp);

    And then convert it back:

    auto earlier = zone->to_sys(local, choose::earliest);
auto later = zone->to_sys(local, choose::latest);

    It's ambiguous iff earlier != later.

    To just tell if a local time is ambiguous, you can also use zone->get_info(local).result == local_info::ambiguous.

    You can also do this with the higher-level zoned_time API instead, which has the benefit of not leaving a local_time floating around with no associated timezone:

    zoned_time original("America/Los_Angeles", sys_seconds(1699173796s));
zoned_time earlier(original.get_time_zone(), original.get_local_time(), choose::earliest);
zoned_time later(original.get_time_zone(), original.get_local_time(), choose::latest);