[Lazarus] Possible error with Now function over summer/winter time change?

[Michael Van Canneyt]

On Sun, 27 Oct 2013, David Taylor wrote:

> I noticed that over the clock change in the Autumn my wall clock continued to 
> display summer time rather than winter time - my guess is that the Now 
> function doesn't check for a change in the minutes offset very frequently, if 
> at all since it was first called.  Restarting the program fixed the problem, 
> but it would be nice to have the fix in the code.

It is a known problem.

Doing this 100% correctly involves re-reading the timezone file at every call of Now() or Date().
Clearly, this is a huge performance impact, severely skewing the time information.

So this is not done.

The "unix" unit contains

Procedure ReReadLocalTime;

which will re-initialize the necessary variables. You can call this routine at regular intervals as you see fit.

In your case, you may want to insert a call to this after every clock update, which would be once a second.

Michael.

>
> This with FPC for the Raspberry Pi.
>
> Source:
>  http://www.satsignal.eu/raspberry-pi/DigitalClock.html
>
> Code extract:
>
> procedure TClockForm.TimerClockTimer (Sender: TObject);
> var
>  when: TDateTime;
>  hours, minutes, seconds, th: Word;
> begin
>  when := Now;
>  DecodeTime (when, hours, minutes, seconds, th);
>  if seconds <> FOldSeconds then
>    begin
>    FOldSeconds := seconds;
>    LabelHHMM.Caption := FormatDateTime ('hh:mm', when);
>    LabelHHMM.Update;
>    LabelSS.Caption := FormatDateTime (' ss', when);
>    LabelSS.Update;
>    if hours <> FOldHours then
>      begin
>      FOldHours := hours;
>      LabelDate.Caption := FormatDateTime ('yyyy-mmm-dd', when);
>      LabelDay.Caption := FormatDateTime ('dddd', when);
>      LabelDate.Left := (ClientWidth - LabelDate.Width) div 2;
>      LabelDay.Left := (ClientWidth - LabelDay.Width) div 2;
>      end;
>    end;
> end;
>
>
> Thanks.
> -- 
> David
> Web: http://www.satsignal.eu
>
>
> --
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