Hello everybody, I have started learning windows programming few days before. I am referring "Let Us C" for making a plot in my mind, then I will switch to "Charles Petzold". I got some doubt in the following code:

#include <windows.h>

HINSTANCE hInst;

LRESULT CALLBACK WndProc ( HWND, UINT, WPARAM, LPARAM );

BOOL InitInstance ( HINSTANCE, int, char*);

void OnDestroy(HWND);

int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR lpCmdLine,int nShowCmd)
{
	MSG m;
	/* perform application initialization */
	InitInstance(hInstance,nShowCmd,"Title");
	/* Message Loop */
	while ( GetMessage(&m,0,0,0) )
		DispatchMessage(&m);
	return 0;
}

LRESULT CALLBACK WndProc(HWND hWnd,UINT message,WPARAM wParam,LPARAM lParam)
{
	switch(message)
	{
	case WM_DESTROY:
		OnDestroy(hWnd);
		break;
	default:
		return ( DefWindowProc(hWnd,message,wParam,lParam) );
	}
	return 0;
}

BOOL InitInstance( HINSTANCE hInstance, int nCmdShow, char* pTitle)
{
	char classname[ ] = "MyWindowClass" ;
	HWND hWnd ;

	WNDCLASSEX wcex ;
	wcex.cbSize			= sizeof ( WNDCLASSEX ) ; 
	wcex.style			= CS_HREDRAW | CS_VREDRAW ;
	wcex.lpfnWndProc	= ( WNDPROC ) WndProc ;
	wcex.cbClsExtra		= 0 ;
	wcex.cbWndExtra	= 0 ;
	wcex.hInstance		= hInstance ;
	wcex.hIcon			= NULL ;
	wcex.hCursor		= LoadCursor ( NULL, IDC_ARROW ) ;
	wcex.hbrBackground	= ( HBRUSH )( COLOR_WINDOW + 1 ) ;
	wcex.lpszMenuName	= NULL ;
	wcex.lpszClassName	= classname ;
	wcex.hIconSm		= NULL ;

	if ( !RegisterClassEx ( &wcex ) )
		return FALSE ;

	hInst = hInstance ; // Store instance handle in our global variable

	hWnd = CreateWindow ( classname, pTitle, 
					WS_OVERLAPPEDWINDOW,
					CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, 
					NULL, hInstance, NULL ) ;
	if ( !hWnd )
	    return FALSE ;
   
	ShowWindow ( hWnd, nCmdShow ) ;
	UpdateWindow ( hWnd ) ;

	return TRUE ;
}

void OnDestroy(HWND hWnd)
{
	PostQuitMessage(0);
}

Q1:-When tracing the above code, I have not passed through the WndProc function. may be in InitInstance(), but after WndProc, "()" is not used(it may be variable).
So I remove def of WndProc from above code.
Code Compiles well but on building the above code two errors occur.
Why so?

Q2:What is that WNDCLASSEX class? where it is defined. and in the above code how it is being used?

Q3: I am bit confused with the Handles. HWND or HINSTANCE.
How many types of handles are there? what are their specific functions??

Thank You,

Waiting for Reply...

: Q1:-When tracing the above code, I have not passed through the
: WndProc function. may be in InitInstance(), but after WndProc, "()"
: is not used(it may be variable).

You only enter WndProc when your window is receiving a message, such as a mouse click. So if you sit in your debugger and stare at the code, the window is likely not receiving any messages, as it will be in the background.


: So I remove def of WndProc from above code.
: Code Compiles well but on building the above code two errors occur.
: Why so?

You must have a WndProc for each window or the code won't work.


: Q2:What is that WNDCLASSEX class? where it is defined. and in the
: above code how it is being used?

That one contains a lot, namely most info about your main window. See the Win API documentation for details.

: Q3: I am bit confused with the Handles. HWND or HINSTANCE.
: How many types of handles are there? what are their specific
: functions??

There are plenty of handles in the Win API. In reality, handle is just a fancy word for pointer. Think of HWND as a pointer to a window and HINSTANCE as a pointer to an application.