[Lazarus] DateDif function needed

[waldo kitty]

On 11/12/2013 3:40 PM, John Landmesser wrote:
> On 12.11.2013 21:01, waldo kitty wrote:
[...]
> Which is correct?
>
> Date1 := 29.2.2000
> Date2 := 28.02.2001
>
> Your function:
> 0 Y, 11 M, 27 D
>
> Rxlib ( Jedi ) DateDiff:
> 0 Y, 11 M, 28 D
>
> Libre Office Calc:
> 0 Y, 11 M, 30 D
>
> The table - function of Libre Office Calc is called in german DATUMDIF()
>
> Get a calendar and count??

actually, i have in some cases... let's ask this question and see what your 
charts and routines return as the result... assuming your format is DD.MM.YYYY...

Date1 := 01.01.2000
Date2 := 01.01.2000

should be 0 (zero), right?

then

Date1 := 01.01.2000
Date2 := 02.01.2000

should be 1 (one), right?

in this case, what i (and bart, too) wrote, we're not counting the starting day 
but we are counting the ending day... this rule stays in effect throughout the 
entire process... my head still aches from rummaging about doing this... it was 
good exercise and one i remember being given on a test many years back to 
determine one's coding level... at that time, the code was being done in dBase 
II/III/IV ;)

i will have to dig deeper and see what is crossing things up for count from 
29.02.2000 to 28.02.2001... i see bart has posted a fix which i have not yet had 
a chance to compare with my code or run thru the tests i included in my posting...

the real question is this:

   what do we count? the starting day, the ending day, both days or neither day?

then we have another question:

   is dayM in monthY a one month difference to dayM in monthX and
   monthZ? monthX, monthY, monthZ are any three consecutive months
   in linear order within one year or crossing two years

once the rules are chosen, then we have something to work with...

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