Get Unhandled exception at 0x00f85069 - c++

Question

my program breaks and says this
Unhandled exception at 0x00f85069 in Monopoly.exe: 0xC0000005: Access violation writing location 0x0000000c.
i made a win32 wrapper. i have two WndProc one is static and the other one not. the static WndProc calls the nonstatic WndProc. when i try to get messages it works fine but when i try to set a value for something it throw a exception.
here is my code for two WndProc(the first one its that static)
LRESULT CALLBACK Window::StaticWndProc( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam )
{
if ( msg == WM_CREATE )
{
SetWindowLongPtr( hWnd, GWLP_USERDATA, (LONG)((CREATESTRUCT *)lParam)->lpCreateParams );
}
Window *targetApp = (Window*)GetWindowLongPtr( hWnd, GWLP_USERDATA );
return targetApp->WndProc( hWnd, msg, wParam, lParam );
}
LRESULT CALLBACK Window::WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_PAINT:
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
case WM_LBUTTONDOWN:
z=-14; //IT THROW EXCEPTION
break;
case WM_RBUTTONDOWN:
z-=1;
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
Thanks in Advance
EDIT:
VARABILES
int z;

Answer 1

How are you creating your window? Did you pass a valid pointer to an instance of Window to your CreateWindow() or CreateWindowEx() function via the lpParam parameter? For example, if your window wrapper has a Create() function or something like that:
void Window::Create()
{
/* ... */
// Pass a pointer to ourselves to CreateWindow() via the lpParam parameter.
// CreateWindow() then passes that pointer to your window procedure
// (StaticWndProc) via WM_CREATE and WM_NCCREATE in the lpCreateParams member
// of CREATESTRUCT. This way the window procedure will know which instance to
// call WndProc() on.
CreateWindow(lpClassName, lpWindowName, dwStyle, x, y, nWidth, nHeight,
hWndParent, hMenu, hInstance, (LPVOID)this);
/* ... */
}

Answer 2

The object on which you're calling WndProc seems to be non-existent (null?) and you have an access violation upon trying to write the memory in z -= 14 which is this->z -= 14 (this being an invalid pointer). That's my guess.
Also, Access Violation is not not an exception in C++ terms. :)

Answer 3

Well, an access violation (0xC0000005) means you accessed memory that you shouldn't have. In this case it says you were trying to write to 0x0000000c. Since you (your debugger?) say that the assignment to z causes it, may we see the definition of that symbol, please? Also, is it really z = -14 or z -= 14?
Edit: I think you need to replace ((CREATESTRUCT *)lParam)->lpCreateParams with a valid pointer to an instance of class Window.
Edit #2: What happens is this: On WM_CREATE, you set GWLP_USERDATA to a value that happens to be equal to NULL. Subsequently, you read that value and treat it as a valid pointer to a Window by invoking a non-static member function on that pointer. Class member functions are implemented by the compiler a lot like so
LRESULT CALLBACK <mangled_name ("Window::WndProc")> (Window * const this, HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam) {
// ...
}
That is the reason that you can actually invoke a member function on a NULL pointer. However, once you access a member variable, like z, this breaks. The compiler inserted code similar to this *((int*) (this + 0xc)) = -14, (which BTW means that z lies 0xc bytes into your Window instance), which, since this == NULL, broke.