Question

I have a server-equipment configuration where I need to change the equip date config, using UDP. The server is written in Java and the equipment, in Delphi.

So, the flow of the data is this:

Java server (Java date) -> UDP (integer date) -> Delphi equipment (Delphi date)

The problem is that when I pass the date as an integer, java calculates miliseconds from 1970, and Delphi, seconds. I pass then the date as following: today.getTime() / 1000, but the equipment understands this as a 2008 date, when we’re on 2012.

I can change the Java code, but the equipment is 3rd party and I don’t have access to it’s source code.

There’s difference between Java and Delphi date parsing that allow this discrepancy?

EDIT:
Thanks to MДΓΓ БДLL I noticed I was multiplying by 1000 instead of dividing by it, I now have a better date, but still wrong (was somewhen in 2033, now it’s in 2008).

Answer 1

A Unix time stamp is the same as the one used in Java. Delphi’s TDateTime, on the other hand, is based on a starting date of 12:01 AM on 12/30/1899 (it’s a COM compatibility thing), so some conversion is necessary. These functions will do it; I’ve also added a quick piece of test code to show the conversion works correctly both ways.

const
  UnixStartDate = 25569.0;

function DateTimeToUnixTime(const ADateTime: TDateTime): Cardinal;
begin
  Result := Round(ADateTime - UnixStartDate) * 86400;
end;

function UnixTimeToDateTime(const UnixDate: Cardinal): TDateTime;
begin
  Result := UnixDate / 86400 + UnixStartDate;
end;

procedure TForm1.Button1Click(Sender: TObject);
var  StartDate: TDateTime;
  UnixDate: Cardinal;
begin
  StartDate := Date();
  Memo1.Lines.Add('Start Date: ' + DateToStr(StartDate));
  UnixDate := DateTimeToUnixTime(StartDate);
  Memo1.Lines.Add('DateTimeToUnixTime = ' + IntToStr(UnixDate));
  Memo1.Lines.Add('UnixTimeToDateTime = ' + DateToStr(UnixTimeToDateTime(UnixDate)));
end;