SetupDiEnumDeviceInterfaces error 259 for display - c++

Question

I am trying to retrieve a set of display related interfaces and seem always to get the 259 error. Since I am very unexperienced with WinApi I could need some hints :)
#include <atlstr.h>
#include <SetupApi.h>
#pragma comment(lib, "setupapi.lib")
#include <stdio.h>
#include <windows.h>
#include <setupapi.h>
#include <devguid.h>
#include <regstr.h>
const GUID GUID_CLASS_MONITOR = {0x4d36e96e, 0xe325, 0x11ce, 0xbf, 0xc1, 0x08, 0x00, 0x2b, 0xe1, 0x03, 0x18};
const GUID GUID_DEVINTERFACE_MONITOR = {0xe6f07b5f, 0xee97, 0x4a90, 0xb0, 0x76, 0x33, 0xf5, 0x7b, 0xf4, 0xea, 0xa7};
int main( int argc, char *argv[ ] )
{
HDEVINFO hDevInfo;
SP_DEVICE_INTERFACE_DATA ifData;
ifData.cbSize = sizeof(ifData);
DWORD dwError;
hDevInfo = SetupDiGetClassDevs(NULL /*&GUID_CLASS_MONITOR*/, NULL, NULL, DIGCF_ALLCLASSES);
dwError = GetLastError();
BOOL bRtn = SetupDiEnumDeviceInterfaces(hDevInfo, NULL, &GUID_CLASS_MONITOR, 0, &ifData); // GUID_DEVINTERFACE_MONITOR did not work either
dwError = GetLastError();
return 0;
}
I cannot see what I am doing wrong SetupDiGetClassDevs has no errors but everything I try regarding SetupDiEnumDeviceInterfaces returns 259.
I've been trying both device setup as well the device interface GUID with no luck.
Edit: Clarification: bRtn returns 0 which means that SetupDiEnumDeviceInterfaces has failed. The 259 error means no more items but my system has two screens attached and since I am calling SetupDiGetClassDevs with no GUID I have expected to get at least my two screen items.
Edit: Added cbSize as suggested

Answer 1

Do you know that ifData.cbSize must be set properly before you call SetupDiEnumDeviceInterfaces?
(http://msdn.microsoft.com/en-us/library/windows/hardware/ff551015(v=vs.85).aspx)
The caller must set DeviceInterfaceData.cbSize to sizeof(SP_DEVICE_INTERFACE_DATA) before calling this function.
(http://msdn.microsoft.com/en-us/library/windows/hardware/ff552342(v=vs.85).aspx)
A SetupAPI function that takes an instance of the SP_DEVICE_INTERFACE_DATA structure as a parameter verifies whether the cbSize member of the supplied structure is equal to the size, in bytes, of the structure.
You did not show setting this value in your code.

Answer 2

For some reason the answer I found by try and error is not intuitive for me but it seems to work.
As I am unable to retrieve the device setup GUID but I had to add DIGCF_DEVICEINTERFACE with conjunction to device interface GUID GUID_DEVINTERFACE_MONITOR to be able to retrieve the interfaces.
Thanks for the hints as missing cbSize would have resulted in another error too :/