Re: [icu-support] DateTime formatting issues with pre-Gregorian dates

[Jamie D. <jam...@gm...>]

I've found what seems to be a workaround...

UDate ToICUDate(const DateTime& DateTime)
{
//const int64 UNIXTimestamp = DateTime.ToUnixTimestamp();
//return static_cast<double>(UNIXTimestamp) * U_MILLIS_PER_SECOND;

UErrorCode ICUStatus = U_ZERO_ERROR;

icu::GregorianCalendar GregCal(ICUStatus);
GregCal.setTimeZone(icu::TimeZone::getUnknown());

int32 Year, Month, Day;
DateTime.GetDate(Year, Month, Day);
GregCal.set(Year, Month - 1, Day, DateTime.GetHour(), DateTime.GetMinute(),
DateTime.GetSecond());

return GregCal.getTime(ICUStatus);
}

The commented out code at the top is how we used to convert to a UDate (via
a timestamp), however if I instead marshal the time through
a icu::GregorianCalendar instance, I get back the UDate that ICU is
expecting and pre-Georgian dates seemingly format correctly (even without
having to change the calendar used by the icu::DateFormat).

I'm not terribly happy with this as a solution though, and I'd still like
to know why the timestamp method is having issues as I don't believe our
representation of time is that unusual.

-Jamie.

On 28 July 2016 at 00:49, Jamie Dale <jam...@gm...> wrote:

> FWIW, before asking here I did try and search through the mailing list,
> and this post from 2006 kept cropping up:
> https://sourceforge.net/p/icu/mailman/message/12529106/
>
> This is strikingly similar to what I'm seeing (1st Jan 0001 is 2 days off
> - I get 3rd Jan 0001), but given this is from 2006, surely it's been fixed
> by now?
>
> -Jamie.
>
> On 27 July 2016 at 23:40, Jamie Dale <jam...@gm...> wrote:
>
>> Hey all,
>>
>> I'm investigating an issue where pre-Gregorian dates are failing to
>> format correctly with icu::DateFormat.
>>
>> We're using ICU 53, and our internal concept of time is ticks of 0.1
>> microseconds since 1st January 0001 - we convert this to a UNIX timestamp
>> and multiply by U_MILLIS_PER_SECOND before passing it to ICU as a UDate.
>>
>> At first I thought this might be due to the Gregorian switch-over, so I
>> tried constructing my own icu::GregorianCalendar, setting the Gregorian
>> change date to 1st January 0001, and then letting the icu::DateFormat adopt
>> that as its calendar, however it didn't seem to make any difference (my
>> calendar reports U_USING_FALLBACK_WARNING when being constructed... I'm not
>> sure why).
>>
>> I'm wondering if anyone else has seen this issue, or whether anyone has
>> any advice?
>>
>> Thanks,
>> Jamie.
>>
>
>