msvc std::chrono::time_zone::get_info 抛出异常说：操作成功完成

Question

在使用std::format显示它之前，我试图将从std::chrono::system_clock返回的utc时间转换为本地时间，但我从std::chrono::time_zone::to_local得到了一个令人惊讶的异常，它的消息是：The operation completed successfully.真是一个惊喜！我研究了这个方法，它在传递的时间参数上调用了std::chrono::time_zone::get_info，并做了一个简单的转换，所以我单独测试了std::chrono::time_zone::get_info，它是这个异常的来源。我不知道这是实现中的错误还是我的代码有错误？

这是抛出此错误的简单代码：

            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();
            }

编辑：查看std::chrono::time_zone::get_info 源代码后，它将调用此方法：std::chrono::time_zone::_Get_info 及其来源

        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};
        }

__std_tzdb_get_sys_info返回的_Info指针不是nullptr，但它的_Err设置为1，等于__std_tzdb_error::_Win_error所以调用_XGetLastError以抛出错误代码来自GetLastError的异常，它将返回 0 表示没有错误代码，因此抛出异常表示没有发生错误！似乎是 Microsoft stl 代码中的错误

Answer 1

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

看起来你应该首先使用 get_tzdb() 作为

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