KB115088 - PRB: A _USRDLL with No CWinApp Object Fails to Load

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It is not necessary for your DLL to call AfxWinInit() and AfxWinTerm() for it to use the MFC collection classes and the simple class types such as CString. If you wish to use only these MFC classes in your DLL, you can omit the instantiation of a CWinApp object, but you also must write your own LibMain() or DllMain() function for the DLL.

For an example of the code that you may want to include in your entry point, you can look at what MFC normally does in AfxWinInit().

NOTE: SetCurrentHandles() is called, so afxCurrentInstanceHandle and afxCurrentResourceHandle get set equal to m_hInstance. You may need to set these values yourself.

Sample Code for Windows

The code below shows one possible implementation of LibMain(). For the sake of pointing out the initialization portion, LibMain() calls MyInit(), which consists of a very simplified simulation of AfxWinInit().

   // Compile options needed: /D "_USRDLL"

   #include <afxwin.h>

   BOOL AFXAPI MyInit(HINSTANCE);

   extern "C" int FAR PASCAL LibMain(HINSTANCE hInstance,
      WORD wDataSegment, WORD wHeapSize, LPSTR lpszCmdLine)
   {
      // Initialize DLL's instance(/module) not the app's
      if (!MyInit(hInstance))
      {
         return 0;    // Init Failed
      }

   // nothing to run
      return 1;   // ok
   }

   BOOL AFXAPI MyInit(HINSTANCE hInstance)
   {
      afxCurrentInstanceHandle = hInstance;
      afxCurrentResourceHandle = hInstance;

   // one instance initialization stuff goes here

   // Handle critical errors
      ::SetErrorMode(SEM_FAILCRITICALERRORS);

      return TRUE;
   }

Sample Code for Windows NT

The code below shows one possible implementation of DllMain(). For the sake of pointing out the initialization portion, DllMain() calls MyInit(), which consists of a very simplified simulation of AfxWinInit().

   // Compile options needed: /D "_USRDLL"

   #include <afxwin.h>

   BOOL AFXAPI MyInit(HINSTANCE);

   extern "C" int APIENTRY
   DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved)
   {
           if (dwReason == DLL_PROCESS_ATTACH)
           {
                   // Initialize DLL's instance(/module) not the app's
                   if (!MyInit(hInstance))
                   {
                           return 0;       // Init Failed
                   }

           }
           return 1;   // ok
   }

   BOOL AFXAPI MyInit(HINSTANCE hInstance)
   {
           afxCurrentInstanceHandle = hInstance;
           afxCurrentResourceHandle = hInstance;

           // one instance initialization stuff goes here

           // Handle critical errors
           ::SetErrorMode(SEM_FAILCRITICALERRORS);

           return TRUE;
   }

PRB: A _USRDLL with No CWinApp Object Fails to Load

SYMPTOMS

CAUSE

RESOLUTION

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Sample Code for Windows

Sample Code for Windows NT