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Re: NSCalendar bug with adding to pre-1919 dates?
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Re: NSCalendar bug with adding to pre-1919 dates?


  • Subject: Re: NSCalendar bug with adding to pre-1919 dates?
  • From: Ben Kazez <email@hidden>
  • Date: Wed, 1 Mar 2006 09:31:19 -0600

This makes sense to me (use UTC intermediately and then convert to the desired time zone). However, I just remembered that in post-1918 dates, there's no DST issue when I add one day or one month to a date across the DST boundaries. This works well for my app, since I always want the time portion of the date to stay the same. Regardless of the adoption of DST in 1918, wouldn't it be more consistent if March 01, 1918 00:00:00 plus 1 year equalled March 01, 1919 00:00:00?

Ben

On Mar 1, 2006, at 2:51 AM, Greg Herlihy wrote:

Since the time calculations are performed for a date and time in a specific
time zone (apparently U.S. Eastern) it would make sense that the time
reported would reflect any Daylight Saving Time adjustment needed to arrive
at the correct, local time. (A little bit of trivia: the "Saving" in
"Daylight Saving Time" does not end in an "s").


If the calculations should be time-zone independent then UTC (GMT) should be
the specified time zone.


Greg


On 2/28/06 10:44 PM, "Brett Powley" <email@hidden> wrote:

Daylight savings perhaps?  Summer DST began for the first time in the
US on March 31 1918, which is right in the middle of where your
weirdness happens...

On 01/03/2006, at 10:06 AM, Ben Kazez wrote:

I have an application that retrieves an NSCalendarDate from a .ics
file and adds one year to it until the date is within a certain
range. (This isn't the most efficient way to do things, but it's
fast enough for my needs.) This algorithm runs into a problem with
dates before 1919. Here's the line that adds the date components:

    currentExpandedDate = [[IEPSystemCalendar
dateByAddingComponents:frequency toDate:currentExpandedDate options:
0] dateWithCalendarFormat:BKWebScriptCalendarFormat timeZone:
[[unexpandedEvent objectForKey:@"DTSTART"] timeZone]];

The frequency variable is set to one year using -[NSDateComponents
setYear:]. As an example, here the app is starting with 1914-03-01
00:00:00 -0600:

March 01, 1915 00:00:00
March 01, 1916 00:00:00
March 01, 1917 00:00:00
March 01, 1918 00:00:00
March 01, 1919 01:00:00
March 01, 1920 01:00:00
...

(Sorry for the inconsistent date formatting.) As you can see, after
1918, the date is one hour off. Does anyone know why this is
happening?

Ben

-------------------------------------------------------------- Brett Powley -- PhD Candidate Centre for Language Technology, Macquarie University, Australia p: +61-402-013050 f: +61-2-90120813 e: email@hidden faciendi plures libros nullus est finis frequensque meditatio carnis adflictio est --------------------------------------------------------------



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