如果你想要改变Windows的缺省打印机,你必须在Windows的WIN.INI中改变设备键。
发送一条 WM_WININICHANGE 消息：

var
  strIni: array[0..MAX_PATH] of Char;
  arrWindows: array[0..64] of Char;
begin
  GetWindowsDirectory(strIni, SizeOf(strIni));
  StrCat(strIni, ''''\win.ini'''');
  with TIniFile.Create(strIni) do
  try
    WriteString(''''windows'''', ''''device'''', ''''HP LaserJet 4 Plus,HPPCL5MS,LPT1:'''');
  finally
    Free;
  end;

  StrCopy(arrWindows, ''''windows'''');
  SendMessage(HWND_BROADCAST, WM_WININICHANGE, 0, LongInt(@arrWindows));
end;