AfxDaoTerm, and stuff

Ted -- tward@geographix.com
Tuesday, April 09, 1996


Sorry if this has been discussed already, but I haven't received the list   
in awhile.

I am using NT 3.51, VC 4.1.

I am trying to open a DAO database in an OCX.  My code does nothing but   
open, and close the database.  When the app that calls the OCX tries to   
exit, the following happens:

Appcore.cpp

int CWinApp::ExitInstance()
{
 if (!afxContextIsDLL)
  SaveStdProfileSettings();

 // Cleanup DAO if necessary
 if (m_lpfnDaoTerm != NULL)
 {
  // If a DLL, YOU must call AfxDaoTerm prior to ExitInstance
  ASSERT(!afxContextIsDLL);

  (*m_lpfnDaoTerm)();  <- *******IMPORTANT PART*******
 }

 return m_msgCur.wParam; // returns the value from PostQuitMessage
}

The function pointer calls into the following code:

Daocore.cpp

void AFXAPI AfxDaoTerm()
{
 _AFX_DAO_STATE* pDaoState = AfxGetDaoState();

 // Close any CDaoWorkspaces left around
 void* pvKey;
 void* pvObject;
 POSITION pos = pDaoState->m_mapWorkspaces.GetStartPosition();
 while (pos != NULL)
 {
  pDaoState->m_mapWorkspaces.GetNextAssoc(pos, pvKey, pvObject);
  ((CDaoWorkspace*)pvObject)->Close();
 }
 pDaoState->m_mapWorkspaces.RemoveAll();

 // Clean up engine object if necessary
 if (pDaoState->m_pDAODBEngine != NULL)
 {
  pDaoState->m_pDAODBEngine->Release();  <- *******CRASHES HERE******
  pDaoState->m_pDAODBEngine = NULL;
 }

 // Shutdown OLE component objects if necessary
 if (pDaoState->m_bOleInitialized)
 {
  ::CoUninitialize();
  pDaoState->m_bOleInitialized = FALSE;
 }

 // If hooked up to CWinApp, make sure to unhook
 CWinApp* pApp = AfxGetApp();
 if (pApp != NULL)
  pApp->m_lpfnDaoTerm = NULL;
}

And the code crashes (access error 00005), I can't even trace into the   
Release() code, the crash happens immediately, but pointer is (obviously)   
not NULL.

The comment in AppCore says that you must call AfxDaoTerm() before   
ExitInstance.  I have tried calling AfxDaoTerm() from different places in   
my code (such as the ExitInstance routine, before calling the default   
handler), and sometimes it has no effect at all, and sometimes I get an   
assertion failure.  But no matter what, it gets called again when the   
application exits.

What is going on???  Anybody??? Thanks for any help.

Please CC any replies to me.


Ted Ward

tward@geographix.com
Denver, Colorado  

---

MikeMike -- MikeMike@athens.emi.net
Friday, April 12, 1996

[Mini-digest: 3 responses]

Ted

Check out Q143084
"Fix:Problems with Using the MFC DAO Classes in a .DLL or .OCX"

You can find it at www.microsoft.com/kb under VC or in MSDN

Mike Massa
MIKEMIKE@MSN.COM
MIKEMIKE@EMI.NET
407-626-2330

-----From: Ola Gunnars 

Im using the Dao in an MFC app (EXE) and there is something wrong in =
this functionality. When runing 3.51 Im calling AfxDaoTerm() and =
everything works fine but whenb runing under NT 4.0 the program crashes =
so I needed to check version before calling this object . My code calls =
ODBC and DAO and I have an query in DAO that calls an ODBC stored proc . =
When I close all databases one ODBC database (CDatabase)  object is =
impossible to close something hangs in SQLDisconnect .
/Ola

-----From: Dan Kirby 

Hi, you must call AfxDaoTerm() after all of your DAO objects are destroyed 
but before ExitInstance(). In other words you can't wait until the 
 DLL_PROCCESS_DETACH case to terminate DAO.

This means that you cannot have Global DAO objects and you can't do 
something like:

void  SomeMethod()
{
	CDaoDatabase db;
	db.Open();
     .
     .
     .
            db.Close();
	AfxDaoTerm();
}
 because AfxDaoTerm is called before the destruction of the DAO object.

If you have:

void  SomeMethod()
{
	CDaoDatabase * pDb= new DaoDatabase;
	db.Open();
     .
     .
     .
            db.Close();
	delete pDb;
	AfxDaoTerm();
}

This is fine.

--dan

---

| Вернуться в корень Архива |