DirectInput help

[200dogz]

I'm trying to use DirectInput in the DirectX SDK to do USB
reading (a device as joystick). There's no error when compiling the codes but whenever it
tries to excecute:

g_pDI->EnumDevices(DI8DEVCLASS_GAMECTRL, EnumJoysticksCallback,
NULL, DIEDFL_ATTACHEDONLY);

where

BOOL CALLBACK EnumJoysticksCallback(const DIDEVICEINSTANCE*
pdidInstance, VOID* pContext)
{
HRESULT hr;

// Obtain an interface to the enumerated joystick.
hr = g_pDI->CreateDevice(pdidInstance->guidInstance,
&joystick, NULL);
if(FAILED(hr))
return DIENUM_CONTINUE;

return DIENUM_STOP;
}

...I get "A first chance exception of
type 'System.NullReferenceException' occurred in test.exe" error
message; the program could still continue but it would just throw
the exception and doesn't do what it is supposed to do.

I've tested it by placing a flag in EnumJoysticksCallback and it
seems to me that it is not the callback function that is causing
the problem.

Appreciate any suggestion :]

[weaknessforcats]

Have you Googled NullReferenceException?

[200dogz]

Have you Googled NullReferenceException?

Yea, one of the answer I found was to disable it completely when compiling the program. However, when I ran the program it stills threw an exception in that line so I'd imagine I need to try and fix it somehow.

[weaknessforcats]

g_pDI, pdidInstance, and guidInstance are all non-zero?

[200dogz]

g_pDI, pdidInstance, and guidInstance are all non-zero?

I don't think I initialised those...so that might be the problem.

Anyway I was told that the way I was doing (following a directInput tutorial) would not work for Form Application that I'm using.

It seems that I need to use something like
virtual void Form1::WndProc(Message% m) override {
if(m.Msg == WM_DEVICECHANGE) {
//do stuff
instead....

Thanks for your help tho =]]

[200dogz]

Perhaps instead of trying to fix the codes I have here that might be completely wrong, I should just ask method of reaching the goal...

I have a Form application with one button and a textbox. How should I approach if I want the program to display the X value of a joystick plugged in the USB port of the PC when the button is pressed? I heard from a friend it should only take around 20 lines to do so.

Thanks for helping :)