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You receive error messages in an MFC application when you upgrade from an earlier version of Visual C++ to Visual C++ 4.2 or a later version

Article ID: 154744

Article Last Modified on 11/21/2006

Microsoft Foundation Class Library 4.2, when used with:
- Microsoft Visual C++ 4.2 Enterprise Edition
- Microsoft Visual C++ 5.0 Enterprise Edition
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 4.2 Professional Edition
- Microsoft Visual C++ 5.0 Professional Edition
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Standard Edition
- Microsoft Visual C++ .NET 2002 Standard Edition
- Microsoft Visual C++ .NET 2003 Standard Edition

This article was previously published under Q154744

SYMPTOMS

The error below may occur in an MFC application where one of the following is assigned a value by the programmer:

   CWinApp::m_pszAppName
   CWinApp::m_pszRegistryKey
   CWinApp::m_pszExeName
   CWinApp::m_pszHelpFilePath
   CWinApp::m_pszProfileName

The following error is displayed in a message box:

   Debug Assertion failed
   Program: my.exe
   File: dbgheap.c
   Line: 1017
   Expression:_BLOCK_TYPE_IS_VALID(pHead->nBlockUse)

In Microsoft Visual C++ 6.0, the following error is displayed in a message box:

   Debug Assertion failed
   Program: my.exe
   File: dbgheap.c
   Line: 1011
   Expression: _CrtIsValidHelpPointer(pUserData)

You may see this error when you upgrade from an earlier version of Visual C++ to Visual C++ versions 4.2 or later.

CAUSE

The CWinApp destructor in MFC included with Visual C++ 4.2 and later now frees the data assigned to the member variables shown above by passing the pointer to the free() function. Doing this prevents memory leaks, which would occur if an MFC regular DLL were dynamically loaded and unloaded.

STATUS

This behavior is by design.

RESOLUTION

If you assign a value to m_pszAppName, m_pszRegistryKey, m_pszExeName, m_pszHelpFilePath, or m_pszProfileName, the data must be dynamically allocated on the heap. You may want to use the _tcsdup() run-time library function to do this.

Also, free the memory associated with the current pointer before assigning a new value. Here is an example:

   // First free the string that was allocated by MFC in the startup
   // of CWinApp. The string is allocated before InitInstance is
   // called.
   free((void*)m_pszProfileName);

   // Change the name of the .INI file--CWinApp destructor will free
   // the memory.
   m_pszProfileName=_tcsdup(_T("d:\\somedir\\myini.ini"));

Additional query words: 4.10 port porting strdup

Keywords: kbtshoot kberrmsg kbprb KB154744