[Interest] QDateTime uses different time zone offset prior to UNIX epoch?

Patrick Stinson patrickkidd at gmail.com
Sat Sep 21 13:32:47 CEST 2019


Ah, I read your response in the forum differently. Thank you.

> On Sep 21, 2019, at 2:18 AM, Christian Ehrlicher <Ch.Ehrlicher at gmx.de> wrote:
> 
> ´╗┐Am 21.09.2019 um 00:12 schrieb Thiago Macieira:
>>> On Friday, 20 September 2019 14:20:40 PDT Patrick Stinson wrote:
>>> QDateTime initializes with a different time zone offset when passed a QDate
>>> before versus after Jan 1 1970. The following line says it all:
>>> 
>>> QDateTime(QDate(1969, 10, 14)).offsetFromUtc() != QDateTime(QDate(1970, 10,
>>> 14)).offsetFromUtc()
>>> 
>>> It seems to me that the offsets for these two QDateTime objects should be
>>> equal. Otherwise, this makes initializing and storing dates difficult.
>>> 
>>> I assume this is intentional. What is the rationale for this design
>>> decision? Is there a workaround?
>> Your test is not reliable. It works for less than half the planet and for just
>> over half the year.
>> 
>> Anyway, there's no workaround. This is done because the timezone databases are
>> inaccurate before 1970. So we just return each timezone's standard time, not
>> accounting for DST.
> This is what I told him at the forum - mktime() on windows simply
> returns the wrong dst value for 1969 (but linux does in this case).
> 
> Christian
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