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Re: NSDateComponents question
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Re: NSDateComponents question


  • Subject: Re: NSDateComponents question
  • From: Chris Kane <email@hidden>
  • Date: Tue, 1 Jul 2008 10:44:16 -0700


On Jul 1, 2008, at 9:26, mmalc crawford wrote:

Hi Chris,

On Jul 1, 2008, at 9:10 AM, Christopher Kane wrote:

The more subtle and serious issue is that Sunday in the current week might be in the previous Month (so, Day < Weekday), or even previous Year, so setting the Day to a negative value and keeping the Month and Year the same will have ... "who knows what effect".

My apologies; I did do some testing and found that the resultant date was always correct.
Could you elaborate on what circumstances this might not be correct?


Did you try starting with a starting date of Jan 1, 2009? The Weekday would be 5, the Day 1.

    January 2009
Su Mo Tu We Th Fr Sa
             1  2  3
 4  5  6  7  8  9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30 31

The previous Sunday is December 28, 2008.

Passing a Year, Month, Day of (2009, 1, -3) (-3 == 1 - (5 - 1) in your original computation) is passing an out-of-bounds value with dateWithComponents:, with who-knows-what effect. It might be well- defined, it might not be. The result might change between OS releases. In other words, it seems a bit ambiguous, so best to just avoid it.


Chris Kane Cocoa Frameworks, Apple

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  • Follow-Ups:
    • Re: NSDateComponents question
      • From: mmalc crawford <email@hidden>
References: 
 >Re: NSDateComponents question (From: Jason Wiggins <email@hidden>)
 >Re: NSDateComponents question (From: mmalc crawford <email@hidden>)
 >Re: NSDateComponents question (From: Christopher Kane <email@hidden>)
 >Re: NSDateComponents question (From: mmalc crawford <email@hidden>)

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