🚀 go-pugleaf

olczyk@interaccess.com (Thaddeus L. Olczyk) wrote:

>Hi. In BCB I am instantiating a class via CComObject eq
>
>CComObject<AImpl> *a =new  CComObject<AImpl>;

That works, but it would be safer to use
CComObject<AImpl> *a;
HRESULT hr=CComObject<AImpl>::CreateInstance(&a);
//test hr as you wish

However, this code will also left a->refcount to zero. Frankly, there
is no much a difference between your and my code, but
CComObjectBase<T>::CreateInstance calls FinalConstruct() that can have
an essential portion of ATL class initialisation.

>
>followed  by returning an interface pointer to a.
>This created a lot of difficulties for me which I discovered from:
>
>CComObject<AImpl> *a =new  CComObject<AImpl>;
>a->AddRef();
>a->Release();
>
>which causes a to be deleted.
>What's going on, it looks like a is created with refcount 0. Shouldn't
>it be 1?

It shouldn't.  You don't get any _interface_ pointer. What you've done
is just a C++ class instantiation. Now you should obtain an interface
pointer using QueryInterface like CoCreateInstance does internally:
IAImpl *pAImpl=NULL;
hr=a->QueryInterface(IID_IAImpl,&pAImpl);
not refcount is 1 and your pointer pAImpl is a valid COM Interface
pointer, not a C++ pointer to class.