The problem is not with the VCL at all. The following code:
var CDate: TDateTime;
CDate := Date - DOB;
is incorrect. Subtracting one date from another does not yield a date, but
rather an interval - a period of time, best expressed as a number. So the
code above is really doing something like:
var CInterval: double;
CDate: TDateTime;
CInterval := Date - DOB; // Interval in number of days, including fraction
CDate := TDateTime(CInterval); // This is wrong - you can't cast an interval
of time to a date sensibly
only a little more concisely. Subtracting 1900 will work for some values,
but since Delphi will (correctly) decode the year as the year given
CInterval days since 30/12/1899, that won't necessarily correlate to the
number of years from your birth date to the current date, due to leap year
differences between the periods "30/12/1899 to 30/12/1899 + CInterval days"
and "DOB to CurrentDate". Thus you'll find you're a day out here and there.
For a whole numbers of identical 365.25 day "years", use
Trunc(CInterval/365.25). For age as we usually refer to the term, Greg
Nixon's GetAge function is correct.
Cheers,
Carl
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> Sent: Friday, 17 December 1999 20:19
> To: Multiple recipients of list delphi
> Subject: Re: [DUG]: Date/Time calculations
>
>
> Patrick, yes,
>
> Unfortunately, the real solution is to recompile the vcl with the
> fix. Because its a number of controls that are affected (not just
> the age calculation).... such as display/modification of dob in a
> grid etc.
>
> What I will be doing is to replace a whole chunk of vcl code by the
> process of intervention. I have deferred it for the holidays.
>
> On 16 Dec 99 at 17:21, Patrick Dunford wrote:
>
> > Has anyone else experienced problems with date/time
> calculations due to
> > Delphi offsetting the date by 30/12/1899
> >
> > The situation is that I wish to calculate a person's
> current age which
> > appeared to be simple: subtract their date of birth from
> the current date
> > then decode into actual years.
> >
> > But Delphi insists on adding this offset to the date so I
> end up with a
> > person having an age of 1901 years.
> > (Delphi 3)
> >
> > Code below:
> >
> > function CurrentAge(DOB:TDateTime):integer; //Return years only
> > var y,m,d:word;
> > CDate:TDateTime;
> > begin
> > CDate:=Date-DOB;
> > DecodeDate(CDate,y,m,d);
> > Result:=y;
> > end;
> >
> > The date subtraction is fine and in one example produces a
> result of 374
> > days, just over 1 year, Delphi then makes this into year
> 1901 but by the
> > calculation the actual number stored in the TDateTime is
> 1.0 something,
> > which it adds 30/12/1899 to
> >
> > The best I have come up with is to subtract 1900 from the
> year but this will
> > be 1 day out.
> >
> >
> >
> --------------------------------------------------------------
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> > New Zealand Delphi Users group - Delphi List -
> [EMAIL PROTECTED]
> > Website: http://www.delphi.org.nz
> >
> Rohit
>
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