Why I can't quit properly?

[Freeman Yan]

When I try the code in the book "Programming Windows" by Charles Petzold, I always can't quit from the program properly.

I used the code like this:

	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;

to quit. The window can be closed every time, but there still a process left in Windows. Then next time, when I want to compile it and run again, the VC6 will give out an error.

What makes this happen? Thank you in advance!

[CBasicNet]

It is hard to determine what is wrong, from the limited information you are giving.

Is it possible for you to post the message loop?

Is it a multithreaded app?

[filthy_mcnasty]

process WM_CLOSE in the same manner instead of WM_DESTROY

[Freeman Yan]

process WM_CLOSE in the same manner instead of WM_DESTROY

Thanks! It works!

But another strange problem appeared. If I don't resize or move the window, I can't close it by clicking the cross at the right top corner. But the Alt+F4 works anyway.

Thank you again!

[Freeman Yan]

Originally posted by CBasicNet
Is it possible for you to post the message loop?

Is it a multithreaded app?

Thank you! It is a very simple program. The message loop is:

	switch (message)
	{
	case WM_RBUTTONDOWN:
		iCount = -1;
		InvalidateRgn(hwnd, NULL, TRUE);
		return 0;

	case WM_LBUTTONDBLCLK:
		//MessageBox(NULL, "Left button pressed!", "Reminder", MB_OK);
		++iCount;
		pt[iCount].x = GET_X_LPARAM(lParam);
		pt[iCount].y = GET_Y_LPARAM(lParam);
		
		//InvalidateRgn(hwnd, NULL, TRUE);
		hdc = GetDC(hwnd);
		Ellipse(hdc, pt[iCount].x-5, pt[iCount].y, pt[iCount].x+15, pt[iCount].y+20);
		TextOut( hdc, pt[iCount].x, pt[iCount].y, TEXT("1"), 1);
		ReleaseDC(hwnd, hdc);
		return 0;

	case WM_PAINT:
		hdc = BeginPaint(hwnd, &ps);

		GetClientRect(hwnd, &rect);

		//TextOut( hdc, nX, nY, TEXT("1"), 1);
		for (i=0; i<=iCount; ++i)
		{
			Ellipse(hdc, pt[i].x-5, pt[i].y, pt[i].x+15, pt[i].y+20);
			TextOut( hdc, pt[i].x, pt[i].y, TEXT("1"), 1);
		}

		EndPaint(hwnd, &ps);
		return 0;

	case WM_CLOSE:
		PostQuitMessage(0);
		return 0;
	}
	return DefWindowProc(hwnd, message, wParam, lParam);

I just practise how to draw texts and graphics in a window.

[Freeman Yan]

I have simplified the code to this, but it still can't be closed properly! There is always something left. I have to use ctrl+alt+delete to find it and remove. Please give me some advice. Thanks!

#include <windows.h>
#include <Windowsx.h>
#include <Mmsystem.h>

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

int WINAPI WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
 	// TODO: Place code here.
	static TCHAR szAppName[] = TEXT("TryToDraw");

	HWND		hwnd;
	MSG			msg;
	WNDCLASS	wndclass;

	wndclass.lpszClassName		= szAppName;
	wndclass.cbClsExtra			= 0;
	wndclass.cbWndExtra			= 0;
	wndclass.hbrBackground		= (HBRUSH) GetStockObject(WHITE_BRUSH);
	wndclass.hCursor			= LoadCursor(NULL, IDC_ARROW);
	wndclass.hIcon				= LoadIcon(NULL, IDI_WINLOGO);
	wndclass.hInstance			= hInstance;
	wndclass.lpfnWndProc		= WndProc;
	wndclass.lpszMenuName		= NULL;
	wndclass.style				= CS_HREDRAW | CS_VREDRAW | CS_DBLCLKS;

	if ( !RegisterClass(&wndclass) )
	{
		MessageBox(NULL, TEXT("Go"), szAppName, MB_ICONERROR);
		return 0;
	}

	hwnd = CreateWindow(
		szAppName,  // registered class name
		TEXT("The Program for Clicking"), // window name
		WS_OVERLAPPEDWINDOW,        // window style
		CW_USEDEFAULT,                // horizontal position of window
		CW_USEDEFAULT,                // vertical position of window
		CW_USEDEFAULT,           // window width
		CW_USEDEFAULT,          // window height
		NULL,      // handle to parent or owner window
		NULL,          // menu handle or child identifier
		hInstance,  // handle to application instance
		NULL        // window-creation data
		);

	ShowWindow(hwnd, nCmdShow);
	UpdateWindow(hwnd);

	while (GetMessage(&msg, hwnd, 0, 0))
	{
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}

	return msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	HDC				hdc;
	PAINTSTRUCT		ps;
	RECT			rect;

	switch (message)
	{
	case WM_CREATE:
		PlaySound(TEXT("hellowin.wav"), NULL, SND_FILENAME | SND_ASYNC);
		return 0;

	case WM_PAINT:
		hdc = BeginPaint(hwnd, &ps);

		GetClientRect(hwnd, &rect);

		EndPaint(hwnd, &ps);
		return 0;

	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;
	}
	return DefWindowProc(hwnd, message, wParam, lParam);
}

[preetham]

instead of using return 0, use break;
I guess only then will the message processing be complete.
In your case(return 0) DefWindowProc() will never be executed.
Regards,
Preetham.
"All you touch and all you see will all you'll ever be"

[filthy_mcnasty]

                                case WM_DESTROY and everything:
		default:
			return DefWindowProc(hwnd, message, wParam, lParam);
	}

	return 0;

}

using return 0 is fine but then you have to set the very bottom of your code to look something like this instead. he's right, the defwindowproc part wont run set up like that.

[Freeman Yan]

Thank you, Preetham!

But the problem is still there after I converted the code into break.
Actually, in my previous case (return 0), the DefWindowProc also can be executed. Otherwise, the program window won't show.

Originally posted by preetham
instead of using return 0, use break;
I guess only then will the message processing be complete.
In your case(return 0) DefWindowProc() will never be executed.
Regards,
Preetham.

[Freeman Yan]

Thank you, filthy_mcnasty!

I tried to create a new project in VC++ 6.0. This time, the project is simple "hellowin" project. Then I copied the message loop part to the new project. The problem disappeared! So I think if the problem is caused by other parts?

Regards,
Freeman

[filthy_mcnasty]

well basically the way you had it set up it wasn't running DefWindowProc to properly close everything out. if any of those messages were hit *WM_DESTROY in the case of the window closing* it wouldn't run that function.

[Freeman Yan]

Dear all,

Thank you for your kindness! I have found the problem. It is caused by

	while (GetMessage(&msg, hwnd, 0, 0))
	{
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}

The second param of GetMessage() should be NULL here... I am sorry for troubling you with such a mistake.

Regards,
Freeman

[filthy_mcnasty]

you're exactly right. goes to show how easy it is to overlook something like that.

glad you got it working.