[Development] QTimeScheme for Qt - 5.0 or 5.1?

Stephen Kelly stephen.kelly at kdab.com
Fri Feb 17 12:56:38 CET 2012

On Friday, February 17, 2012 07:06:16 Konrad Rosenbaum wrote:
> On Wednesday 15 February 2012, Stephen Kelly wrote:
> > On Wednesday, February 15, 2012 21:55:54 Konrad Rosenbaum wrote:
> > >  The
> > > 
> > > calculation results are almost identical. Almost.
> > 
> > Is that enough?
> > 
> > John Layt mentioned the existence of such a mapping too.
> It depends on how you define "enough". 

My question was mostly rhetorical.

> Both systems yield the same time for
> the richer countries (US, central Europe, Japan) as long as you stay within
> the limits of the last 30 years or so. Beyond that Olson tends to have more
> accurate data on time shifts. This means that the time returned by Windows
> and Olson DB can differ by one or two hours for dates further in the past
> and for some countries that are "less important" for Microsoft.
> I'd actually recommend three engines:
> a) the default engine is basically what we have in Qt4 - it just knows
> "local" and "UTC" - its backend uses the system functions
> b) OlsonDB would be the first advanced engine
> c) Windows could come later to have one that is identical to the default
> engine for the local zone on Windows

Yes, this is essentially what I proposed, except that I proposed only a) being 
part of Qt, and b) and c) to be outsourced - made possible by implementing the 
QTimeZone (nee QTimeScheme) abstract interface.

> > > *it is not always clear which time spec is standard and which one is
> > > DST
> > 
> > I'm not certain what you mean.
> The definition of time zones is unfortunately up to politicians, so it does
> get fuzzy around the edges: while most countries either do not observe DST
> or have standard time in (local) summer and DST in winter, there are
> countries that have standard time in (local) winter and some kind of Anti-
> DST in summer. At times countries do not switch off the time spec they
> happen to be on for several years (e.g. during World War II several
> countries remained on DST and called it War Time).

Yes, but in the interface I proposed the output timezone depends on the input 
datetime, so the result can be as good as Olson can represent, right?

Have you looked at my patch yet?


Stephen Kelly <stephen.kelly at kdab.com> | Software Engineer
KDAB (Deutschland) GmbH & Co.KG, a KDAB Group Company
www.kdab.com || Germany +49-30-521325470 || Sweden (HQ) +46-563-540090
KDAB - Qt Experts - Platform-Independent Software Solutions
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