PRB: C2535 Error When Compiling ATL Project with Visual C++ 6.0

• The Microsoft Active Template Library (ATL) 3.0, included with:
  • Microsoft Visual C++, 32-bit Editions, version 6.0

SYMPTOMS

You may get compiler error C2535 on a class developed in Active Template Library (ATL) when compiled in ATL version 3.0. In previous versions of ATL, a compiler error was not generated for the same class. For example, if your class looks like the following, you will get the error with Visual C++ version 6.0.

//CCOMTest
class CCOMTest : public CComObjectRootEx<CComMultiThreadModel>
{
public:
    // Constructor, Destructor
    CCOMTest() {};
    ~CCOMTest() {};
    
    // Interface Map
    BEGIN_COM_MAP(CCOMTest)
    END_COM_MAP()

    DECLARE_NO_REGISTRY()
        
    // IUnknown methods
    STDMETHODIMP QueryInterface(REFIID piid, void **ppv);
    STDMETHODIMP_(ULONG) AddRef(void);
    STDMETHODIMP_(ULONG) Release(void);

 private:
    LONG   mlRef;         //Reference count
}; 

CAUSE

The implementation of END_COM_MAP between Visual C++ version 5.0 and Visual C++ version 6.0 has changed. In Visual C++ 5.0, END_COM_MAP was defined as the following:

#ifdef _ATL_DEBUG_QI
#define END_COM_MAP()   {NULL, 0, 0}};	return &_entries[1];}
#else
#define END_COM_MAP()   {NULL, 0, 0}};	return _entries;}
#endif // _ATL_DEBUG_QI 

#define END_COM_MAP() {NULL, 0, 0}}; 
return _entries;} 	
virtual ULONG STDMETHODCALLTYPE AddRef( void) = 0; 	
virtual ULONG STDMETHODCALLTYPE Release( void) = 0; 	
STDMETHOD(QueryInterface)(REFIID, void**) = 0;
#endif // _ATL_DEBUG 

RESOLUTION

In Visual C++ version 6.0, you can comment out the IUnknown methods that were implemented or add something like the following code sample:

#ifdef _ATL_DEBUG
#define END_MY_COM_MAP() {NULL, 0, 0}}; return &_entries[1];} 
#else
#define END_MY_COM_MAP() {NULL, 0, 0}}; return _entries;} 
#endif // _ATL_DEBUG

// CCOMTest
class CCOMTest: public CComObjectRootEx<CComMultiThreadModel>
{
public:

    // Constructor, Destructor
    CCOMTest() {};
    ~CCOMTest() {};

    // Interface Map
    BEGIN_COM_MAP(CCOMTest)
    END_MY_COM_MAP()

    DECLARE_NO_REGISTRY()
        
    // IUnknown methods
    STDMETHODIMP QueryInterface(REFIID piid, void **ppv);
    STDMETHODIMP_(ULONG) AddRef(void);
    STDMETHODIMP_(ULONG) Release(void);

private:
    LONG   mlRef;     //Reference count
}; 

STATUS

This behavior is by design.

Additional query words: C4661

Keywords : kbCOMt kbVC600 kbATL300 kbDSupport kbGrpMFCATL
Version : WINDOWS:3.0
Platform : WINDOWS
Issue type : kbprb