Recurring events with timezone

Tobias König tobias.koenig at
Wed Oct 27 16:12:03 CEST 2010

On Wednesday 27 October 2010 12:24:10 Hendrik Helwich wrote:
> Am Donnerstag, 21 Oktober 2010 15:52:12 schrieb Tobias König:

> Hi Tobias,
Hej Hendrik,

> To do this you must know in which tz this event should happen to know which
> DST rules should be applied.
No, you only need to know when this event was created and what the DST rules 
of your local (or the one you want to see the event in) timezone are.
Everything else can be calculated with these two information.

> If you use the system local tz DST rules like it is implemented right now
> in the clients, people in different tzs would use different rules and the
> UTC times could be different for the same event.
Not if they do the calculation correctly. Currently they just do a
  'UTC + offset -> localtime'
where 'offset' is a fixed number depending on the DST. While this works for 
single events, it is the problem for recurring events.
So in the latter case, clients have to calculate the 'offset' depending on the 
DST _and_ the point in time when the event has been created.

If clients don't do this, it's a bug in the clients but not a limitation of 
the format.

> You need to convert the start time like
> event tz -> UTC -> client tz
No, there is no event tz, events are always stored in UTC.

Tobias Koenig | tobias.koenig at
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel. Germany +49-30-521325470, Sweden (HQ) +46-563-540090
KDAB - Qt Experts - Platform-independent software solutions

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