[Lazarus] DateDif function needed

[John Landmesser]

On 12.11.2013 13:05, Bart wrote:
>
> I proposed a "solution" in this thread.
> It'll give you (at least that was the intention) the years, months,
> and days between two (Gregorian) dates.
>
> Bart
>
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Hi Bart,

i found this in old RxLib ( now Yedi ).

Perhaps it inspires you.

procedure DateDiff(Date1, Date2: TDateTime; var Days, Months, Years: word);
var
   DtSwap: TDateTime;
   Day1, Day2, Month1, Month2, Year1, Year2: word;
begin
   if Date1 > Date2 then
   begin
     DtSwap := Date1;
     Date1 := Date2;
     Date2 := DtSwap;
   end;
   DecodeDate(Date1, Year1, Month1, Day1);
   DecodeDate(Date2, Year2, Month2, Day2);
   Years := Year2 - Year1;
   Months := 0;
   Days := 0;
   if Month2 < Month1 then
   begin
     Inc(Months, 12);
     Dec(Years);
   end;
   Inc(Months, Month2 - Month1);
   if Day2 < Day1 then
   begin
     // von mir auskommentiert Inc(Days, DaysPerMonth(Year1, Month1));
     Inc(Days, DaysInAMonth(Year1, Month1));
     if Months = 0 then
     begin
       Dec(Years);
       Months := 11;
     end
     else
       Dec(Months);
   end;
   Inc(Days, Day2 - Day1);
end;


My Tests showed: this procedure works well !

The next function seems also much better than that in DateUtil:

function MonthsBetween(Date1, Date2: TDateTime): Double;
var
   D, M, Y: Word;
begin
   DateDiff(Date1, Date2, D, M, Y);
   Result := 12 * Y + M;
   if (D > 1) and (D < 7) then Result := Result + 0.25
   else if (D >= 7) and (D < 15) then Result := Result + 0.5
   else if (D >= 15) and (D < 21) then Result := Result + 0.75
   else if (D >= 21) then Result := Result + 1;
end;

Problem: it returns Double!!

I'll use these two and i think everything is ok?!!

happy hacking ...

John