Author: Tomas Rutkauskas 

I want to assign a new time to the system time. How would I do this? I tried to get 
the system time through GetSystemTime() and set the new time to SetSystemTime(), 
but I get the wrong results.

Answer:

Solve 1:

This sets the time to the same time in year 1999:
1   
2   procedure TForm1.Set1999(Sender: TObject);
3   var
4     stSystemTime: TSystemTime;
5   begin
6     Windows.GetLocalTime(stSystemTime);
7     stSystemTime.wYear := 1999;
8     Windows.SetLocalTime(stSystemTime);
9   end;



Solve 2:

By using the following call (example is a method of a button click) you may 
directly modify the date and time of Windows. 
10  
11  procedure TForm1.Button1Click(Sender: TObject);
12  var
13    NewTime: TSystemTime;
14  begin
15    FillChar(NewTime, sizeof(NewTime), #0);
16    NewTime.wYear := 2000;
17    NewTime.wMonth := 8;
18    NewTime.wDay := 28;
19    NewTime.wHour := 0;
20    NewTime.wMinute := 0;
21    NewTime.wSecond := 0;
22    NewTime.wMilliseconds := 0;
23  
24    SetLocalTime(NewTime);
25  end;


Please note that when you do chage the system time, send a WM_TIMECHANGE message to 
all toplevel windows so that they can detect the time change...  You should do this 
for all version of windows but 2000 since it does it by its self.  Bellow is the 
code: 
26  
27  if IsWin2000 = False then
28    SendMessage(HWND_TOPMOST, WM_TIMECHANGE, 0, 0);
29  
30  function IsWin2000(): Boolean;
31  var
32    OSInfo: TOSVersionInfo;
33  begin
34    Result := False;
35    OSInfo.dwOSVersionInfoSize := SizeOf(OsInfo);
36    if not GetVersionEx(OSInfo) then
37    begin
38      Exit;
39    end;
40    if OsInfo.dwPlatformID = VER_PLATFORM_WIN32_NT then
41    begin
42      if OSInfo.dwMajorVersion >= 5 then
43        Result := True;
44    end;
45  end;