Memory leaks are reported when you use multiple MFC DLLs

   a CDynLinkLibrary object at $00410F70, 64 bytes long
   a CDynLinkLibrary object at $00410F70, 64 bytes long
   {38} client block at 0x00410D80, subtype 0, 64 bytes long.
   a CDynLinkLibrary object at $00410D80, 64 bytes long
   a CDynLinkLibrary object at $00410D80, 64 bytes long
   {36} client block at 0x00410C60, subtype 0, 64 bytes long.
   a CDynLinkLibrary object at $00410C60, 64 bytes long
   a CDynLinkLibrary object at $00410C60, 64 bytes long
				

   int CTestDllApp::ExitInstance()
   {
      TRACE(_T("ExitInstance() for regular DLL: TESTDLL\n"));

      return CWinApp::ExitInstance();
   }
				

MORE INFORMATION

Consider the following application/DLLs:

     -------------               --------------
     =           =               =            =
     =   MFC     =    Calls      =    MFC     =
     =   APP     = ------------> =   USRDLL   =
     =           =               =            =
     =           =               =            =
     -------------               --------------
           |                           |
           |                           |
           | Calls                     | Calls
           |                           |
           \/                         \/ 
     -------------               --------------
     =           =               =            =
     =           =               =            =
     =   MFC40d  =               =   MFC40Ud  =
     =    DLL    =               =    DLL     =
     =           =               =            =
     -------------               --------------
                \                 / 
                 \               / 
                  \ Calls       / Calls
                   \           / 
                   \/         \/ 
                   -------------
                   =           =
                   =           =
                   =  MSVCR40d =
                   =   (CRT)   =
                   =           =
                   -------------
				

The MFC Application that is built with the ANSI (MFC40d.DLL) version of MFC calls the MFC USRDLL, which is built with the UNICODE (MFC40Ud.DLL) version of MFC. Both MFC versions use the same C run-time (CRT) DLL, MSVCR40d.DLL. Since MFC USRDLLs are "black-boxes", there should be no problems with calling a UNICODE MFC USRDLL from an ANSI MFC Application.

However, since the UNICODE (MFC40ud.DLL) and ANSI (MFC40d.DLL) MFC DLLs both use the same CRT DLL, false memory leaks are reported on all the objects allocated in the MFC USRDLL. This occurs because MFC relies on the CRT DLL to allocate and track all memory. It does not separate the memory allocations from the different versions of MFC. When one of the MFC DLLs unloads, it calls the CRT to do a memory dump, assuming everything left in the heap is a memory leak. However, this assumption is incorrect since there are two multiple copies of MFC in memory.

(c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Kelly Marie Ward, Microsoft Corporation.