Brtdku

This is probably a silly question and I hesitated to post, but I'm a newbie at ATL.

I need to implement an interface in my code. I do not have a TLB or IDL for tha t interface, I just have a header file.

The header file defines the interface as follows:

EXTERN_C const IID IID_IExternalCon;

 ...    



     MIDL_INTERFACE("BCAC73A8-0226-4250-9D66-9656AA9BB86C")

        IExternalCon: public IUnknown

        {

        public:

            virtual HRESULT STDMETHODCALLTYPE GetName( 

                /* [in] */ __RPC__in ULONG *interface);

           //  ...



        }

And I need to implement multiple instances of it. Unfortunately the loader that is looking for my interface is not finding my implementation of this interface.

I have done something like this:

// is this a proper forward reference?

[

    object,

    uuid(BCAC73A8-0226-4250-9D66-9656AA9BB86C), // is this uuid supposed to match the one in the header?

    dual,

    nonextensible,

    pointer_default(unique)

]

interface IExternalCon: IUnknown

{

};





library ... {

    [

        uuid(d543911a-81b0-4de1-9511-d1f14caceed)

    ]



    // the class implementing my interface

    coclass ExternalConTest

    {

        [default] interface IExternalCon;

    };

}

Any help, hints, or guidance on dealing with implementing interfaces just based on a header file would be appreciated.

Incidentally, my class is defined as follows:

class ATL_NO_VTABLE CExternalConTest :

    public CComObjectRootEx<CComSingleThreadModel>,

    public CComCoClass<CExternalConTest, &CLSID_ExternalConTest>,

    public IExternalCon

{

public:

...



BEGIN_COM_MAP(CExternalConTest)

    COM_INTERFACE_ENTRY(IExternalCon)

    COM_INTERFACE_ENTRY(IUnknown)

END_COM_MAP()

..

}

What you have to do to implement an external interface in an ATL object is

• add the interface to the list of implemented interface (you did that). This will modify the class binary layout (vtable, etc.)


• add the interface to BEGIN_COM_MAP list. This will instruct the ATL underlying QueryInterface implementation to answer positively for queries for that interface id (you did that). IUnknown is no necessary here.


• add the interface declaration to the .h file. Linkage and annotation are optional there, I personally remove them. I also always add a remark with the interface name so we know what method is used by what interface. When you have a lot it's useful...


• add the interface implementation to the .cpp file.

So in your case it would be this for the .h file:

class ATL_NO_VTABLE CExternalConTest :

    public CComObjectRootEx<CComSingleThreadModel>,

    public CComCoClass<CExternalConTest, &CLSID_ExternalConTest>,

    public IExternalCon // change the class layout

{

public:

...



BEGIN_COM_MAP(CExternalConTest)

    COM_INTERFACE_ENTRY(IExternalCon) // answer to QueryInterface calls

END_COM_MAP()

...



public:

    // IExternalCon

    HRESULT GetName(ULONG *interface);

...

    // IWhatever

    HRESULT Blabla( ... );

    HRESULT Blabla2( ... );



...

and this for the .cpp file:

// CExternalConTest

...

// IExternalCon

HRESULT CExternalConTest::GetName(ULONG *interface)

{

    // TODO : implement this

    return S_OK;

}

...

// IWhatever

HRESULT CExternalConTest::Blabla(...)

{

    // TODO : implement this

    return S_OK;

}



HRESULT CExternalConTest::Blabla2(...)

{

    // TODO : implement this

    return S_OK;

}

Concerning the .idl, you don't have to do anything because Visual Studio uses it as the base for code generation. Usually, when using Visual Studio, you first change the .idl (using wizards or not) and then fill the gaps.