Access Violation 0xC0000005

whiteclouds

Hi all! I'm developing an console application with MFC support. Now I meet an exception when I execute the following code:

CBitmap 	\*bitmap;
CDC 		memDC;
CRect		rect;
CWnd \*pWnd=m\_pWndHide;//->GetWindow(GW\_HWNDFIRST);

// CWindowDC dc(pWnd);

memDC.CreateCompatibleDC(&m\_hDC);//(&dc);

// Calculate required height from specified width
int height = CAH\_glo\_y \* width / CAH\_glo\_x;

bitmap = new CBitmap();
//The next line will occur "Access Violation 0xC0000005"
bitmap->CreateCompatibleBitmap(&m\_hDC, width, height );//(&dc, width, height );
CBitmap\* pOldBitmap = memDC.SelectObject(bitmap);
// using the current background colour (assume white for the moment)
memDC.PatBlt(0, 0, width,height, WHITENESS);
...

I trace this error into a source file named SBHEAP.c in MFC then. The function stopped in is __sbh_alloc_block. The related code is following:

        ...
        pEntry->pEntryNext = pHead->pEntryNext;
        pEntry->pEntryPrev = pHead;
        pHead->pEntryNext = pEntry;
        pEntry->pEntryNext->pEntryPrev = pEntry;//Stop here
        ...

I watch the value of pHead->pEntryNext . It is NULL. So I can't access it. But I don't know why and how to resolve it.:confused: This code will be executed many times before. But it is wrong when the 3 times. If someone can tell me or give me some good advice, I will be very glad. Thanks! Regards whiteclouds

Nibu babu thomas

whiteclouds wrote:

bitmap->CreateCompatibleBitmap(&m_hDC, width, height );//(&dc, width, height );

Note that if width and height is too big then CreateCompatibleBitmap does fail. Also how did you get m_hDC. Is this a valid DC?

Nibu babu thomas Microsoft MVP for VC++ Code must be written to be read, not by the compiler, but by another human being. Programming Blog: http://nibuthomas.wordpress.com

whiteclouds

Hi, thomas! Thanks for your reply. I think I had found the reason. After I delete some variables that aren't be used any more, the exception is missing. But another exception is occur same as this when I use the code following:

	time\_t	ltime;		// local time
	struct	tm	\*gmt;	// Greenwich Mean Time
	png\_time	ttime;	// png format

	time (&ltime);	// get the local time---EXCEPTION 0xC0000005 OCCUR HERE!
	gmt = gmtime (&ltime);	// convert to gmt
	png\_convert\_from\_struct\_tm (&ttime, gmt);  // convert to png format
	png\_set\_tIME (png\_ptr, info\_ptr, &ttime);

I trace this exception into MFC and I found when a function named _mlock was invoked in the __tzset function, the exception occur. The related code like this:

        \_mlock( \_TIME\_LOCK );

I don't know the reason and hope you or others can give me some suggestion. Thank you! Regards! whiteclouds