[Lazarus] DateDif function needed

John Landmesser JohnML at online.de
Tue Nov 12 14:58:25 CET 2013

```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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> Lazarus at lists.lazarus.freepascal.org
> http://lists.lazarus.freepascal.org/mailman/listinfo/lazarus

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

```