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Re: NSNumberFormatter & NSTimestamp -- Not Happening
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Re: NSNumberFormatter & NSTimestamp -- Not Happening


  • Subject: Re: NSNumberFormatter & NSTimestamp -- Not Happening
  • From: Chuck Hill <email@hidden>
  • Date: Wed, 17 Sep 2003 09:02:26 -0700

When doing things like this I prefer noon, rather than midnight, as a
reference time:

NSTimeZone timeZone = NSTimeZone.systemTimeZone();
outDate = new NSTimestamp(dateYear, dateMonth, dateDay, 12, 0, 0, timeZone);

Then it does not matter it if gets moved to 11AM or 1PM, the day is still
the same.

Does that make it better for your case?


Chuck


At 07:19 PM 17/09/2003 +1200, Denis Stanton wrote:
>Hi Albert
>
>Thank you for taking the time to look into this.
>
>On Wednesday, September 17, 2003, at 04:52  PM, Albert Jagnow wrote:
>
>> I am pretty sure that NSTimestamp is stored in UTC which is not
>> affected by daylight savings time.  If you compare two timestamps
>> where one was stored on October 25 2003 at 2:00AM local time and the
>> other was stored on October 26 2003 at 1:00AM local time after the
>> time change, these dates are 24 hours apart even though one is at 2:00
>> local time and the other is at 1:00 local time.  If you look at the
>> UTC time for each in a database (assuming local time is central time)
>> you should see something like 2003-10-25 07:00:00 for the first time
>> and 2003-10-26 07:00:00 for the second.  The difference calculation
>> below should give you a diff of 24 hours or 1 day.  This is the
>> correct difference is it not?
>
>That's not the way it works out in practice.  I am prepared to believe
>that that I am causing this through my own ignorance, but my experience
>so far suggests that not all days are equal.
>
>I am developing an application for booking rental cars.  The user sets
>outDate and returnDate by selecting day number, month name and year
>number from three pop-up menus.  These are used to form dates with
>approximately the following code:
>
>         NSTimeZone timeZone = NSTimeZone.systemTimeZone();
>         outDate = new NSTimestamp(dateYear, dateMonth, dateDay, 0, 0,
>0, timeZone);
>
>If I set an outDate of 1 October and a return date of 7th October, and
>then use System.out.println to display the results without formatting I
>will see:
>
>2003-01-01 12:00:00 Etc/GMT
>2003-01-07 11:00:00 Etc/GMT
>
>The user intends renting for a whole week, but performing the
>calculation discussed would return a duration of  6.9583 days,
>truncated to 6 days.
>
>The workaround is to always add 1 hour before performing the division.
>Some weeks will then be 7 days and others 7.0416.  All will truncate to
>7.
>
>Maybe the better answer is to set a timezone of UTC in the first place,
>but I haven't figured out how to do this so I'm using system time.
>
>Denis
>_______________________________________________
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>

--

Chuck Hill                                 email@hidden
Global Village Consulting Inc.             http://www.global-village.net
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  • Follow-Ups:
    • Re: NSNumberFormatter & NSTimestamp -- Not Happening
      • From: Denis Stanton <email@hidden>
    • Re: NSNumberFormatter & NSTimestamp -- Not Happening
      • From: Jonathan Rochkind <email@hidden>
References: 
 >Re: NSNumberFormatter & NSTimestamp -- Not Happening (From: Denis Stanton <email@hidden>)

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