Please confirm if this is a date bug

[Ken Ray]

On Mon, 04 Jun 2007 11:06:34 -0500, Len Morgan wrote:

> I've been trying to validate a user date entry and I'm not getting 
> what I  think the  correct result should be:
> 
> in the message box (for simplicity's sake):
> 
> put "05/19/1956" is a date
> false
> 
> This is on Windows XP with 2.8.1.  This DOES work (i.e., returns 
> true) on a Mac.
> 
> If the year is 1970 or higher, it will return true (as it should).
> 
> This seems like it might be related to bug 4911 which reported that 
> if you passed "" to is a date, it returned "12/31/1969" instead of 
> "invalid date"
> 
> Is there a work-around?

1970 is the Windows "beginning of time" that affects all (AFAIK) 
WIndows programs that deal with dates without writing or using a custom 
library (i.e. it's a Windows kernel issue). You can get around this by 
simply adding 1000 to the year; if you can't add 1000 to the year - it 
means the last part of the "date" is not a number (and you can return 
that it's not a date). If it *does* add the 1000, you can use the rest 
of the month/day to validate that with the "is a date" function. The 
only trouble you might have is leap year days (Feb 29), which would 
take a different calculation:

function isLeapYear pYear
  return ((pYear mod 400 = 0) or ((pYear mod 4 = 0) and (pYear mod 100 
<> 0)))
end isLeapYear

HTH,

Ken Ray
Sons of Thunder Software, Inc.
Email: kray at sonsothunder.com
Web Site: http://www.sonsothunder.com/