Thread: Debug assertion failed

This program example from my Nitty Gritty book compiles without errors or warnings but when you click on the SYSTEM_FONT button I get this error:

Debug Assertion Failed!
Line 47
Expression _BLOCK_TYPE_IS_VALID(pHead->nBlockUse)
For info see asserts.



So I looked up asserts in one of my C++ books and it says:
" A macro that stringizes and displays as an error message the expression passed in as a parameter if that expression evaluates to false."

I did a search on this site and got 9 hits including this link that seems closely related but doesn't seem to help me:

http://cboard.cprogramming.com/showt...hlight=asserts

Seeing line 47 in the error made me double check it but according to my book this is correct. So somewhere I must be 'passing in a false condition' but I do

not see an error.




Please shed some light on this for me!

Code:

#include <windows.h>

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

HINSTANCE hInstGlobal;
HWND hEdit;

int APIENTRY WinMain(HINSTANCE hInstance,
			  HINSTANCE hPrevInstance,
			  LPSTR lpCmdLine,
			  int nCmdShow)			// nShowCmd???
{
	hInstGlobal = hInstance;

	WNDCLASS WndClass;
	WndClass.style = 0;
	WndClass.cbClsExtra = 0;
	WndClass.cbWndExtra = 0;
	WndClass.lpfnWndProc = WndProc;
	WndClass.hInstance = hInstance;
	WndClass.hbrBackground = (HBRUSH) (COLOR_WINDOW+1);
	WndClass.hCursor = LoadCursor (NULL, IDC_ARROW);
	WndClass.hIcon = LoadIcon (NULL, IDI_APPLICATION);
	WndClass.lpszMenuName = 0;
	WndClass.lpszClassName = "WinProg";

	RegisterClass(&WndClass);

	HWND hWindow;
	hWindow = CreateWindow("WinProg", "Edit Field",
		WS_OVERLAPPED,
		0,0,640,400,NULL,NULL,
		hInstance, NULL);

	ShowWindow (hWindow, nCmdShow);

	UpdateWindow (hWindow);

	MSG Message;
	while (GetMessage(&Message, NULL, 0, 0))
	{
		DispatchMessage(&Message);
	}

	return (Message.wParam);
}

LRESULT CALLBACK WndProc (HWND hWnd, UINT uiMessage, WPARAM wParam, LPARAM lParam)
{
	switch(uiMessage)
	{
	case WM_CREATE:
		HWND hButton, hButtonExit; 
		hButton = CreateWindow("BUTTON","SYSTEM_FONT",
			WS_CHILD | WS_VISIBLE |BS_PUSHBUTTON,		// BS_PUSHBUTTON returns BN_CLICKED			
			10,320,140,20,
			hWnd, (HMENU) 1,

			hInstGlobal, NULL);
		hButtonExit = CreateWindow("BUTTON","EXIT",
			WS_CHILD | WS_VISIBLE |BS_PUSHBUTTON,
			160,320,140,20,
			hWnd, (HMENU) 2,
			hInstGlobal, NULL);
		hEdit = CreateWindow("EDIT","SYSTEM_FONT",
			WS_CHILD | WS_VISIBLE | WS_BORDER | ES_AUTOHSCROLL,
			10,340,120,20,
			hWnd, (HMENU) 1,
			hInstGlobal, NULL);
		return 0;

	case WM_COMMAND:
	if(HIWORD(wParam) == BN_CLICKED)		// BN = Button Notification.  BS_PUSHBUTTON returns BN_CLICKED
		{
			if(LOWORD(wParam) == 1)
			{
				HDC hdc;
				hdc = GetDC (GetParent((HWND) lParam));
				HFONT hFont;
				hFont = (HFONT) GetStockObject(SYSTEM_FONT);
				
				char *string1;
				string1 = new char[255];
				SendMessage (hEdit, WM_GETTEXT, 256,(LPARAM) string1);
				bool FontDa;
				FontDa =0;
				if (lstrcmp (string1,"SYSTEM_FONT") == 0)
				{
					hFont = (HFONT) GetStockObject(SYSTEM_FONT);
					FontDa = 1;
				}
				if (lstrcmp (string1,"SYSTEM_FIXED_FONT") == 0)
				{
					hFont = (HFONT) GetStockObject(SYSTEM_FIXED_FONT);
					FontDa = 1;
				}
				if (lstrcmp (string1,"OEM_FIXED_FONT") == 0)
				{
					hFont = (HFONT) GetStockObject(OEM_FIXED_FONT);
					FontDa = 1;
				}
				if (lstrcmp (string1,"ANSI_VAR_FONT") == 0)
				{
					hFont = (HFONT) GetStockObject(ANSI_VAR_FONT);
					FontDa = 1;
				}
				if (lstrcmp (string1,"ANSI_FIXED_FONT") == 0)
				{
					hFont = (HFONT) GetStockObject(ANSI_FIXED_FONT);
					FontDa = 1;
				}
				if (lstrcmp (string1,"DEFAULT_GUI_FONT") == 0)
				{
					hFont = (HFONT) GetStockObject(DEFAULT_GUI_FONT);
					FontDa = 1;
				}
				if (FontDa == 0)
				{
					hFont = (HFONT) GetStockObject(SYSTEM_FONT);
					lstrcpy (string1, "SYSTEM_FONT");
				}
				SelectObject (hdc, hFont);
				RECT rect;
				SetRect (&rect, 0,0,480,280);
				HBRUSH hBrush;
				hBrush = CreateSolidBrush(RGB(255,255,255));
				FillRect (hdc, &rect, hBrush);
				TextOut (hdc, 340,10,string1, lstrlen(string1));
				delete [] string1;
				TEXTMETRIC tm;
				GetTextMetrics (hdc, &tm);
				int i;
				int ix,iy;
				ix = 0;
				iy = 0;
				char *string;
				string = new char[2];
				string[1] = 0;
				for(i=0;i<=255;i++)
				{
					string[0] = i;
					TextOut (hdc, ix, iy, string, lstrlen(string));
					iy = iy + tm.tmHeight;
					if ((iy/tm.tmHeight)==16)
					{
						iy = 0;
						ix = ix + 20;
					}
				}


				ReleaseDC (GetParent((HWND) lParam), hdc);
				delete [] string1;
			}
			if (LOWORD(wParam) == 2)
			{
				SendMessage (GetParent((HWND) lParam),	// hWnd is the handle of a window object to which the message is sent.
					WM_DESTROY ,0 ,0);					// Msg is the value which identifies the message.
			}											// wParam is the first parameter of the 

message.
		}												// lParam is the second parameter of the 

message.
		return 0;

	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;
	default:
	
		return DefWindowProc (hWnd, uiMessage, wParam, lParam);
	}
}

Compiling...
Edit Field.cpp
Linking...

Edit Field.exe - 0 error(s), 0 warning(s)

/code

Worked fine on my computer. Windows 2000 Professional.

I'm running Win XP Pro with MS VC++ 6.0.

I suppose this could be a XP problem? When I get back home I could load Visual Studio on my desktop(Win2k Pro and Win 98) and see how it runs there.

Thanks for trying this on your system MrWizard.

I compiled it in MSVC6 and .NET and ran it under XP pro and it ran fine.

I just ran it under compatibility mode for Win2k and it works great I'll have to remember this for future reference.