SetupDiGetDeviceInterfaceDetail always returns error code 1784

From: Slava Antonov (ai_at_omskmail.ru)
Date: 01/25/04 

Date: Sun, 25 Jan 2004 09:37:41 +0600

H e l l o, A l l !

Here the code, with comments:
=========Beginning of the citation==============
procedure TForm1.Button2Click(Sender: TObject);
const
  ComClassGUID: TGuid =
'{4D36E978-E325-11CE-BFC1-08002BE10318}';//'{4D36E96D-E325-11CE-BFC1-0
8002BE10318}';
var
  DeviceInfo: HDEVINFO;
  DeviceInterfaceData: SP_DEVICE_INTERFACE_DATA;
  DeviceInterfaceDetailData: PSPDeviceInterfaceDetailData;
  Size: Cardinal;
begin
    DeviceInfo:= SetupDiGetClassDevs(@ComClassGUID,
                   nil,
                   0,
                   DIGCF_DEVICEINTERFACE or DIGCF_PRESENT);
  if Cardinal(DeviceInfo) = INVALID_HANDLE_VALUE then
    Exit;

  try
    DeviceInterfaceData.cbSize:= SizeOf(DeviceInterfaceData);
    if not SetupDiEnumDeviceInterfaces(DeviceInfo,
               nil,
               ComClassGUID,
               0,
               DeviceInterfaceData) then
      RaiseLastOSError;

// ask how many bytes needed
    SetupDiGetDeviceInterfaceDetail(DeviceInfo,
               @DeviceInterfaceData,
               nil,
               0,
               @Size,
               nil);

// allocate the memory
    GetMem(DeviceInterfaceDetailData, Size);
    try

// set cbSize (size of the DeviceInterfaceDetailData^ is a 5 bytes)
      DeviceInterfaceDetailData.cbSize:=
SizeOf(DeviceInterfaceDetailData^);

// here we get error 1784. Why?
      if not SetupDiGetDeviceInterfaceDetail(DeviceInfo,
          @DeviceInterfaceData,
          @DeviceInterfaceDetailData,
          Size,
          nil,
          nil) then
        RaiseLastOSError;
      Caption:= PChar(@DeviceInterfaceDetailData.DevicePath);
    finally
      FreeMem(DeviceInterfaceDetailData);
    end;
  finally
    SetupDiDestroyDeviceInfoList(DeviceInfo);
  end;
end;

=========The end of the citation================ 

--
With best regards, Slava.
Quantcast