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7.4

COM client gets the class object, but always fails on CoCreateInstanceEx with E_NOINTERFACE

Asked by Codewarp in DCOM, Microsoft Visual C++

Tags: C++ programming, COM client/server development, E_NOINTERFACE, CoCreateInstanceEx

I am responsible for a COM client/server application, completely written in C++ and IDL, with nothing too sacred for modification. The trouble is, when a client calls for the first interface using CoCreateInstanceEx, it always fails with E_NOINTERFACE. I have verified that the local server is indeed installed and launched, and verified a correct QueryInterface( ) call for the interface in question on the object (during the aforementioned CoCreateInstanceEx call), which goes on to successfully return the correct interface pointer, and S_OK.

But still, CoCreateInstanceEx always returns E_NOINTERFACE. We use Visual Studio 8, over Windows XP for current development. Only local servers are currently being tested, i.e. only out-of-process COM servers, no remote or in-process servers). I have built COM client/server applications in the past, but never encountered so much difficulty. What conditions could lead to this consistent failure? This is just fundamental COM, it should not be so hard, what am I missing?

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             More background, with failure exits and other details omitted for simplicity...
 
Here's the skeleton client:
 
    HRESULT hr = CoInitializeEx (0, (COINIT_APARTMENTTHREADED);
    CoInitializeSecurity (    // Initialize security
        0, -1, 0, 0, RPC_C_AUTHN_LEVEL_NONE,
        RPC_C_IMP_LEVEL_IDENTIFY, 0, EOAC_NONE, 0
    ); 
    CoCreateInstanceEx with: CLSID_MyClass, CLSCTX_LOCAL_SERVER, IID_MyInterface
    which always fails and the client exits.
    ...
 
Here's the skeleton server process:
 
    CoInitializeEx (0, (COINIT_APARTMENTTHREADED);
    CoInitializeSecurity (    // Initialize security
        0, -1, 0, 0, RPC_C_AUTHN_LEVEL_NONE,
        RPC_C_IMP_LEVEL_IDENTIFY, 0, EOAC_NONE, 0
    );
    CoRegisterClassObject( ), with CLSID_MyClass, the class instance( ), 
        REGCLS_MULTIPLEUSE, CLSCTX_LOCAL_SERVER
    while (GetMessage (&msg, 0, 0, 0)) {    // pump Windows messages for life
        DispatchMessage(&msg);  TranslateMessage (&msg);
    }
    CoRevokeClassObject releases class object(s)
    CoUninitialize ( )
    process exits
 
Some of the things tried:
 
  -  Different security settings; eliminating explicit security altogether, etc.
  -  Used the long method instead of calling CoCreateInstanceEx,
        i.e. via CoGetClassObject/IID_IClassFactory/CreateInstance, which reports
        an "Interface not registered" error (0x80040155), rather than E_NOINTERFACE  
  -  Different CLSCTX and REGCLS settings
  -  Reviewed and verified all the install parameters, using oleview.
  -  Reviewed internal operation with debugger, code traces, etc.
  -  Read Essential COM (by Don Box), all over again, and again.

           
         

20091021-EE-VQP-81 - Hierarchy / EE_QW_3_20080625

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COM client gets the class object, but always fails on CoCreateInstanceEx with E_NOINTERFACE

Asked by Codewarp in DCOM, Microsoft Visual C++

Tags: C++ programming, COM client/server development, E_NOINTERFACE, CoCreateInstanceEx

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