CODEWITHSUNDEEP
c++visual-c++c++-chrono
dev65
dev65

Reputation: 1605

msvc std::chrono::time_zone::get_info throws an exception saying: The operation completed successfully

I was trying to convert utc time returned from std::chrono::system_clock to local time before displaying it using std::format but I got a surprising exception from std::chrono::time_zone::to_local and its what message says: The operation completed successfully. What a surprise ! I looked into this method and it called std::chrono::time_zone::get_info on the passed time parameter and did a simple conversion so I tested std::chrono::time_zone::get_info separately and it was the source of this exception. I don't know is it a bug in the implementation or my code is buggy ?

Here is a simple code which throws this error:

            try
            {
                const std::chrono::time_zone* current_z = std::chrono::current_zone();
                std::cout << "current timezone name: " << current_z->name() << "\n";
                auto sys_time = std::chrono::system_clock::now();
                std::cout << "current system time: " << sys_time << "\n";
                auto sys_info = current_z->get_info(sys_time); // throws exception what(): The operation completed successfully.
                std::cout << "sys_info: offset: " << sys_info.offset << ", abbrev" << sys_info.abbrev << "\n";
                //auto local_time = current_z->to_local(sys_time); // throws exception since it calls get_info
                //std::cout << "current local time: " << local_time << "\n";
            }
            catch (const std::exception& ex)
            {
                std::cout << "caught exception: " << ex.what();
            }

EDIT: After looking at std::chrono::time_zone::get_info source code it will invoke this method: std::chrono::time_zone::_Get_info and its source

        template <class _Duration>
        _NODISCARD sys_info _Get_info(const _Duration& _Dur) const {
            using _Internal_duration = duration<__std_tzdb_epoch_milli, milli>;
            const auto _Internal_dur = _CHRONO duration_cast<_Internal_duration>(_Dur);
            const unique_ptr<__std_tzdb_sys_info, _Tzdb_deleter<__std_tzdb_sys_info>> _Info{
                __std_tzdb_get_sys_info(_Name.c_str(), _Name.length(), _Internal_dur.count())};
            if (_Info == nullptr) {
                _Xbad_alloc();
            } else if (_Info->_Err == __std_tzdb_error::_Win_error) {
                _XGetLastError();
            } else if (_Info->_Err == __std_tzdb_error::_Icu_error) {
                _Xruntime_error("Internal error loading IANA database information");
            }

            constexpr auto _Min_internal =
                _CHRONO duration_cast<_Internal_duration>(_Min_seconds.time_since_epoch()).count();
            constexpr auto _Max_internal =
                _CHRONO duration_cast<_Internal_duration>(_Max_seconds.time_since_epoch()).count();
            const auto _Begin =
                _Info->_Begin <= _Min_internal
                    ? _Min_seconds
                    : sys_seconds{_CHRONO duration_cast<sys_seconds::duration>(_Internal_duration{_Info->_Begin})};
            const auto _End =
                _Info->_End >= _Max_internal
                    ? _Max_seconds
                    : sys_seconds{_CHRONO duration_cast<sys_seconds::duration>(_Internal_duration{_Info->_End})};
            return {.begin = _Begin,
                .end       = _End,
                .offset    = _CHRONO duration_cast<seconds>(_Internal_duration{_Info->_Offset}),
                .save      = _CHRONO duration_cast<minutes>(_Internal_duration{_Info->_Save}),
                .abbrev    = _Info->_Abbrev};
        }

the _Info pointer returned by __std_tzdb_get_sys_info is not nullptr but its _Err is set to 1 which equals __std_tzdb_error::_Win_error so _XGetLastError is called to throw an exception with the error code from GetLastError and it will return 0 indicating no error code so an exception is thrown indicating that no error has happened ! seems a bug in microsoft stl code

Upvotes: 1

Views: 896

Answers (2)

Patrick Colis
Patrick Colis

Reputation: 1

Windows uses a timezone "short name" internally. The short name of "America/New_York" timezone is for exemple "UTF−5". But between "UTF" and "5", it's not a "-" but a "−" (U+2212)

The wide to narrow string conversion may fail depending on your local code page.

I solve the problem forcing the application code page to UTF-8.

setlocale(LC_ALL, ".utf8");

Hope this will help.

Upvotes: 0

Namascar
Namascar

Reputation: 13

Per https://learn.microsoft.com/en-us/cpp/standard-library/time-zone-class?view=msvc-170

Looks like you should first use get_tzdb() as in

const auto& timeZoneDatabase = get_tzdb(); // initialize the time zone database
const auto& currentZone = timeZoneDatabase.current_zone();

Upvotes: 1

Related Questions