KB156067 - FIX: Setting Tooltip Text in OnToolHitTest Causes Assertion

Article ID: 156067

Article Last Modified on 11/21/2006

Microsoft Foundation Class Library 4.2, when used with:
- Microsoft Visual C++ 4.0 Standard Edition
- Microsoft Visual C++ 4.1 Subscription
- Microsoft Visual C++ 4.2 Enterprise Edition
- Microsoft Visual C++ 4.2 Professional Edition

This article was previously published under Q156067

SYMPTOMS

Attempting to set the text for a tooltip in the OnToolHitTest function of a CWnd by assigning a resource ID to the TOOLINFO struct's lpszText member causes the following assertion to occur:

   Debug assertion failed
   File: dbgheap.c
   Line: 1011

For example, setting the TOOLINFO struct as follows:

   pTI->lpszText= MAKEINTRESOURCE(SomeId);
   pTI->hinst=AfxGetInstanceHandle();

where pTI is a pointer to the TOOLINFO struct, will cause the problem. Setting the TOOLINFO struct members in this manner allows the programmer to specify a resource that the tooltip uses to get the text for the tooltip.

CAUSE

The CWnd::FilterToolTipMessage() function contains the following code:

   if (tiHit.lpszText != LPSTR_TEXTCALLBACK)
       free(tiHit.lpszText);

Because lpszText is not set to LPSTR_TEXTCALLBACK, the free function is called. However, a resource ID, rather than a string, was specified in the OnToolHitTest() function, and therefore the assertion occurs.

RESOLUTION

Instead of specifying a resource ID to load, load the resource and assign the text to the TOOLINFO struct's lpszText member as follows:

   pTI->lpszText = (char *)malloc(200, sizeof(char));
   if (::LoadString(AfxGetInstanceHandle(),pTI->uId, pTI->lpszText,200)==0)
   {
      ASSERT(FALSE);   //String resource doesn't exist
   }

MFC frees the allocated buffer after it has added the tool (that is, after it has sent the TTM_ADDTOOL message).

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem has been fixed in Visual C++ version 5.0.

Additional query words: kbVC400bug tool tip

Keywords: kbbug kbfix kbnoupdate kbtooltip kbuidesign kbvc500fix KB156067