[Lazarus] UnixToDateTime and time zone

[Dibo]

Dnia 2010-09-17, pią o godzinie 01:55 +0300, Alberto Narduzzi pisze: 
> Dibo,
> 
> > Is there a function in FPC that returns me my local UTC offset?
> 
> never tested them, thou' have a look at DateTimeToUnix and 
> UnixToDateTime, in unit DateUtils
> 
> HTH

UnixToDateTime and DateTimeToUnix don't uses any GMT/UTC calculation.
They just convert date time just as it is. I search internet for time
zone information in delphi and I found this article:
http://delphicikk.atw.hu/listaz.php?id=2667&oldal=52

I change his code to free pascal cross platform and this is working
function (tested on windows and linux):

uses dateutils, {$IFDEF MSWINDOWS} windows {$ENDIF} {$IFDEF UNIX}
unixutil {$ENDIF}

function UniversalTimeToLocal(UT: TDateTime): TDateTime;
var
  LT: TDateTime;
  TZOffset: Integer;
  {$IFDEF MSWINDOWS}
  BiasType: Byte;
  TZInfo: TTimeZoneInformation;
  {$ENDIF}
begin
  LT := UT;
  {$IFDEF MSWINDOWS}
  BiasType := GetTimeZoneInformation(TZInfo);
  if (BiasType=0) then begin
    Result := UT;
    Exit;
  end;

  // Determine offset in effect for DateTime UT.
  if (BiasType=2) then
    TZOffset := TZInfo.Bias + TZInfo.DaylightBias
  else
    TZOffset := TZInfo.Bias + TZInfo.StandardBias;
  {$ENDIF}
  {$IFDEF UNIX}
    TZOffset := -Tzseconds div 60;
  {$ENDIF}

  // Apply offset.
  if (TZOffset > 0) then
    // Time zones west of Greenwich.
    LT := UT - EncodeTime(TZOffset div 60, TZOffset mod 60, 0, 0)
  else if (TZOffset = 0) then
    // Time Zone = Greenwich.
    LT := UT
  else if (TZOffset < 0) then
    // Time zones east of Greenwich.
    LT := UT + EncodeTime(Abs(TZOffset) div 60, Abs(TZOffset) mod 60, 0,
0);

  // Return Local Time.
  Result := LT;
end;


Demo:

procedure TForm1.Button1Click(Sender: TObject);
var
  d: TDateTime;
begin
  // This is unix time 2010-07-26 17:50:17
  d := UnixToDateTime(1280166617);
  d := UniversalTimeToLocal(d);
  // After convert we get 2010-07-26 19:50:17 (Poland GMT + 2h)
  Edit1.Text := DateTimeToStr(d);
end;

I am surprised that Free Pascal does not have so basic function. Should
I post it on mantis as proposition?

> Cheers, A.
> 
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