CComObject and reference counting

Thread View: comp.os.ms-windows.programmer.ole

2 messages

[T] Back to Threads [V] Tree View [G] Group Articles

2 total messages Started by Thaddeus L. Olczyk Thu, 30 Jul 1998 00:00

#21

Author: Thaddeus L. Olczyk
Date: Thu, 30 Jul 1998 00:00

14 lines
1091 bytes

Hi. In BCB I am instantiating a class via CComObject eq

CComObject<AImpl> *a =new  CComObject<AImpl>;

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?

Re: CComObject and reference counting

#22

Author: Mike Tyukanov
Date: Thu, 30 Jul 1998 00:00

35 lines
1816 bytes

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.

Thread Navigation

This is a paginated view of messages in the thread with full content displayed inline.

Messages are displayed in chronological order, with the original post highlighted in green.

Use pagination controls to navigate through all messages in large threads.

Back to All Threads