27 Time library [time]

27.11 Time zones [time.zone]

27.11.3 Exception classes [time.zone.exception]

27.11.3.2 Class ambiguous_­local_­time [time.zone.exception.ambig]

namespace std::chrono {
  class ambiguous_local_time : public runtime_error {
  public:
    template<class Duration>
      ambiguous_local_time(const local_time<Duration>& tp, const local_info& i);
  };
}
1
#
ambiguous_­local_­time is thrown when an attempt is made to convert an ambiguous local_­time to a sys_­time without specifying choose​::​earliest or choose​::​latest.
🔗
template<class Duration> ambiguous_local_time(const local_time<Duration>& tp, const local_info& i);
2
#
Preconditions: i.result == local_­info​::​ambiguous is true.
3
#
Effects: Initializes the base class with a sequence of char equivalent to that produced by os.str() initialized as shown below: 
ostringstream os;
os << tp << " is ambiguous.  It could be\n"
   << tp << ' ' << i.first.abbrev << " == "
   << tp - i.first.offset << " UTC or\n"
   << tp << ' ' << i.second.abbrev  << " == "
   << tp - i.second.offset  << " UTC";
4
#
[Example
: 
#include <chrono>
#include <iostream>

int main() {
  using namespace std::chrono;
  try {
    auto zt = zoned_time{"America/New_York",
                         local_days{Sunday[1]/November/2016} + 1h + 30min};
  } catch (const ambiguous_local_time& e) {
    std::cout << e.what() << '\n';
  }
}
Produces the output:
2016-11-06 01:30:00 is ambiguous.  It could be
2016-11-06 01:30:00 EDT == 2016-11-06 05:30:00 UTC or
2016-11-06 01:30:00 EST == 2016-11-06 06:30:00 UTC
— end example
]