Microsoft KB Archive/151070

= FIX: DYNAMIC_DOWNCAST & STATIC_DOWNCAST Causes Stack Overflow =

Article ID: 151070

Article Last Modified on 11/21/2006

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APPLIES TO


 * Microsoft Foundation Class Library 4.2, when used with:
 * Microsoft Visual C++ 4.1 Subscription

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This article was previously published under Q151070



SYMPTOMS
When the DYNAMIC_DOWNCAST and STATIC_DOWNCAST macros are called, and a pointer to a "const" object is passed, you see an error message similar to the following in debug mode:

Unhandled exception in downcast.exe (MFC40D.DLL); Stack Overflow.

In release builds, the application hangs.



CAUSE
The DYNAMIC_DOWNCAST and STATIC_DOWNCAST macros invoke the AfxDynamicDownCast and AfxStaticDownCast functions respectively. A code defect in Visual C++ version 4.1 causes these calls to be recursive if the object pointer passed as the second parameter to either macro points to a "const" object. The end result is a stack overflow.



RESOLUTION
To work around this problem, remove the "const" attribute for the object pointer in the call to the appropriate DOWNCAST macro. You can do this by using the "const_cast" operator as follows: //CMyDlg is derived from CDialog const CMyDlg dlg;

//pdlg is a pointer to a const object const CMyDlg* pdlg = &dlg;

DYNAMIC_DOWNCAST(CDialog, const_cast(pdlg));

// or

STATIC_DOWNCAST(CDialog, const_cast(pdlg));



STATUS
Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug was corrected in Visual C++ 32-bit Edition version 4.2.

Additional query words: MfcMisc

Keywords: kbbug kbfix kbnoupdate kbvc420fix KB151070

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