[RESOLVED]Callback Type Problem

[Max_aka_NOBODY]

First off, I'm a newbie C++ coder, so I'm sorry if what I'm asking is obvious, but searching has given me no solution. I'm trying to write a simple window class with the message handler passed by the class user, so I define a member variable as "LRESULT(*)(HWND, UINT, WPARAM, LPARAM)", which is supposed to be the function pointer. Then I assign the passed value(same type) to this member, which results in the error: "invalid conversion from `LRESULT (*)(HWND__*, UINT, WPARAM, LPARAM)' to `LRESULT (*)(HWND__*, UINT, WPARAM, LPARAM)'". I read that it could be caused by the function address being that of a non-static member function, but I've tried both a normal function and a member, and both result in the same error.

Here's the code that concerns this problem(it's scattered around a few files, but that's unimportant I think all are linked by inclusion):

typedef LRESULT(*grCallbackWndProc)(HWND, UINT, WPARAM, LPARAM);

LRESULT CALLBACK MessageHandler(HWND hWnd, UINT iMessage, WPARAM wParam, LPARAM lParam);

grErrorCode grWindow::Create(HINSTANCE hInstance,
                       grCallbackWndProc WndProc,
                       LPSTR sTitle,
                       int iWidth,
                       int iHeight,
                       int iStyle) {
        if (0 == WndProc) {
            //This line gives the error.
            mWndProc = &MessageHandler;
        } else {
            mWndProc = WndProc;
        }
        //Rest of code that compiles fine.
} 

This is using the GCC compiler.

Thanks for any insight.

[sunburnt]

To save you a serious headache, you cannot use a non-static member function as the window procedure, because of the hidden "this" pointer that needs to be passed to each member function.

Otherwise, if you're not using a member function, your code looks fine. Maybe try adding CALLBACK after LRESULT in your typdef -- CALLBACK is defined as __stdcall while the default calling convention is 'cdecl.' This might be the problem.

edit: I think you put the calling convention inside the parentheses -- ie,

typedef LRESULT( CALLBACK *grCallbackWndProc)(HWND, UINT, WPARAM, LPARAM);

but I'm not sure

[CornedBee]

sunburnt's answer is correct.

But also, there's no need for the typedef. windows.h already contains one by the name of WNDPROC.

[Max_aka_NOBODY]

Thanks a lot. Works like a charm.