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Q156067: FIX: Setting Tooltip Text in OnToolHitTest Causes Assertion

Article: Q156067
Product(s): Microsoft C Compiler
Version(s): winnt:4.0,4.1,4.2
Operating System(s): 
Keyword(s): kbMFC kbToolTip KbUIDesign kbVC400bug kbVC410bug kbVC420bug kbVC500fix kbGrpDSMFCATL kb
Last Modified: 06-MAY-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
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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          : kbMFC kbToolTip KbUIDesign kbVC400bug kbVC410bug kbVC420bug kbVC500fix kbGrpDSMFCATL kbNoUpdate 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:4.0,4.1,4.2
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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