WinMain and return msg.wParam problems

Hi

I'm a begining C++ programer. I'm working from a book called Beginning Game Programing by Johnathan Harbour. I'm up to using the DirectX API. I have the latest Direct X SDK, the book was written with 9.0b and beyond in mind. Im using Visual C++ 6.

The program is meant to have a black background (windowed at 640 x 480) and have a sprite of a cat walking. All that happens is that the screen flicks up and then disapears. Its not meant to do this. I will go back and check for a return 0 instead of something else in my code but i dont think that is the problem...

This is the code of my WinMain...

Code:

// Beging Game Programing
// Chapter 7
// winmain.cpp -- windows code framework



// header files

#include <d3d9.h>
#include <d3dx9.h>
#include <time.h>
#include <stdio.h>
#include "dxgraphics.h"
#include "game.h"



//windows event call back function
LRESULT WINAPI WinProc( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam )
	{
		switch ( msg )

		{
		case WM_DESTROY:
			//release the direct 3d device
			if (d3ddev != NULL)
				d3ddev->Release();

			//release the direct 3d object
			if (d3d != NULL)
				d3d->Release();

			//call the 'front end' shut-down function
			Game_End(hWnd);

			// tell windows to kill this program
			PostQuitMessage(0);
			return 0;
		}
		
	return DefWindowProc (hWnd, msg, wParam, lParam);
 
	}


//helper function to set up the window properties
ATOM MyRegisterClass(HINSTANCE hInstance)
	{
		//create the window class structure
		WNDCLASSEX wc;
		wc.cbSize = sizeof(WNDCLASSEX);

		//fill the struct with info
		wc.style = CS_HREDRAW | CS_VREDRAW;
		wc.lpfnWndProc = (WNDPROC)WinProc;
		wc.cbClsExtra = 0;
		wc.cbWndExtra = 0;
		wc.hInstance = hInstance;
		wc.hIcon = NULL;
		wc.hCursor = LoadCursor(NULL, IDC_ARROW);
		wc.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);
		wc.lpszMenuName = NULL;
		wc.lpszClassName = APPTITLE;
		wc.hIconSm = NULL;

//set up the window with the class info
return RegisterClassEx(&wc);
}


//entry point for a windows program
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)

{
	MSG msg;
	HWND hWnd;

	//Register the class
	MyRegisterClass(hInstance);

	//set up the screen in windowed or full-screen mode?
	DWORD style;
	if (FULLSCREEN)
		style = WS_EX_TOPMOST | WS_VISIBLE | WS_POPUP;
	else
		style = WS_OVERLAPPED;

	//Create new window
	hWnd = CreateWindow(
		APPTITLE,				//window class
		APPTITLE,				//title bar
		style,					//window style
		CW_USEDEFAULT,			//x position of window
		CW_USEDEFAULT,			//y position of window
		SCREEN_WIDTH,			//width of the window
		SCREEN_HEIGHT,			//height of the window
		NULL,					//parent window
		NULL,					//menu
		hInstance,				//application instance
		NULL);					//window parameters

	//Was there an error creating the window?
	if (!hWnd)
		return false;

	//display the window
	ShowWindow(hWnd, nCmdShow);
	UpdateWindow(hWnd);

	if (!Init_Direct3D(hWnd, SCREEN_WIDTH, SCREEN_HEIGHT, FULLSCREEN))
		{
		MessageBox(hWnd, "Error initializing Direct 3D", "Error", MB_OK);
		return 0;
		}
	//initalize the game
	if (!Game_Init(hWnd))
		{
			MessageBox(hWnd, "Error initializing the game", "Error", MB_OK);
			return 0;
		}

	//main message loop
	int done = 0;
	
	while (!done)
		{
			if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
			{
				//look for quit message
				if (msg.message == WM_QUIT)
					done = 1;

				//decode and pass messages on to WndProc
				TranslateMessage(&msg);
				DispatchMessage(&msg);
			}

			else
				//process game loop ('else' prevents running after close)
				Game_Run(hWnd);

			return 0;
		}
	return msg.wParam;

}

The one line that has a warning is
return msg.wParam, just at the end. It says...

warning C4700: local variable 'msg' used without having been initialized

This is the only warning/error in my entire program and it doesnt work. I can post the other files if need be, but i think it is this one line.

Any help would be appreciated, will go and check for other errors manualy now.

Cheers
Manaxter

Ok, i must appologise...not a good start.

I added a return 0 just after Game_Run(hWnd). Ooops.

But, if you could tell me why i get that warning, that would be good!

Cheers
Manaxter

The compiler is just telling you that the loop

Code:

while (!done)

might not be executed and in this case

Code:

return msg.wParam;

would return an uninitialized value.
So I guess

Code:

do {
  ...
} while ( ! done );

Would be a better solution.
Kurt

Which is actually pretty stupid of the compiler. A simple flow analysis using the fact that nothing between done's initialization and the loop would prove that msg MUST be initialized (provided that PeekMessage assigns a value, which it cannot know, but should assume).

this is what my message loop looks like:

Code:

MSG msg;
    while ( 1 ) 
    {
        // Did we recieve a message, or are we idling ?
        if ( PeekMessage( &msg, NULL, 0, 0, PM_REMOVE ) ) 
        {
            if ( msg.message == WM_QUIT)
            {
                break;
            }
            TranslateMessage( &msg );
            DispatchMessage ( &msg );
        } 
        else 
        {
            // Render the frame
            if ( m_pGraphics->GetDevice() != NULL && m_active )
            {
                OnUpdateFrame();
                OnRenderFrame();
            }
        } 
    }

It compiles just fine. Also note that my DX is wrapped in classes so ignore the code for rendering.