ATL/COM : In IDL file can we create a class which can be used as return type

Question

I was working on COM/ATL. I need to use a class object as return value so that it can be used in managed code. I am able to define structure in idl file and also able to use it as return parameter when creating methods. Below is the partial idl file implementation:

    import "oaidl.idl";
    import "ocidl.idl";

//Structure for message mapping of activation and deactivation 
//Structures are working properly
[uuid(E2240D8B-EB97-4ACD-AC96-21F2EAFFE100)]
struct tagActivationManaged
{

    WORD            wMsgId;
    WORD            wStatus;
    WORD            wClient;
    WORD            wClientId;

};


//same manner if creating class it throws error.
[uuid(2ED2E59C-9362-46b2-80D8-471AD69BA5D5)]
class AuthenticationMessage
{
    public: 
    Word message;
}

do I need to change any settings in MIDL.

NB: I am new to COM programming.

Answer 1

You just can't do that - there're no C++ flavor classes in IDL. If you want to return an object of some class from a function you have to declare an interface and possibly a coclass (the latter may not be required depending on your sitiation) and make the function return that interface.