DOCUMENT:Q154744  11-JUN-2002  [visualc]
TITLE   :PRB: Modifying CWinApp Members Causes Error in DBGHEAP.C
PRODUCT :Microsoft C Compiler
PROD/VER::4.2,5.0,6.0
OPER/SYS:
KEYWORDS:kberrmsg kbMFC kbVC420 kbVC500 kbVC600 kbGrpDSMFCATL

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - The Microsoft Foundation Classes (MFC), used with:
    - Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0, 6.0 
    - Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0, 6.0 
    - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
    - Microsoft Visual C++.NET (2002) 
-------------------------------------------------------------------------------

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 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.

RESOLUTION
==========

This behavior is by design. 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          : kberrmsg kbMFC kbVC420 kbVC500 kbVC600 kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : :4.2,5.0,6.0
Issue type        : kbprb

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

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 2002.