VC ATL, Passing COM objects as parameters to other COM objects

Passing COM objects as parameters to other COM objects

Author	Message
Paul Fle #1 / 8	Passing COM objects as parameters to other COM objects Hi I need to transfer a reference to a COM object as a parameter to another COM object in C++. What do I need to implement on both sides? On the 'sender side' to allow the object to be passed by reference, and on the 'receiver side' what is actually received? I can't find any reference on MSDN or on previous newsgroup posts... Cheers, Paul.
Sun, 23 Nov 2003 18:31:00 GMT

#2 / 8	Passing COM objects as parameters to other COM objects
Fri, 19 Jun 1992 00:00:00 GMT

Thomas Hanse #3 / 8	Passing COM objects as parameters to other COM objects Pass them as IUnknown and dynamically_cast them back to what they were... Quote: > Hi > I need to transfer a reference to a COM object as a parameter to another COM > object in C++. What do I need to implement on both sides? On the 'sender > side' to allow the object to be passed by reference, and on the 'receiver > side' what is actually received? > I can't find any reference on MSDN or on previous newsgroup posts... > Cheers, > Paul.
Sun, 23 Nov 2003 19:07:40 GMT

Paul Fle #4 / 8	Passing COM objects as parameters to other COM objects OK, so is there any sample code around at all? What I actually need to do is send from Visual Basic Scripting. i.e. Result = MyObject2.MyMethod(MyObject1) On the C++ receiver side would this actually receive a pointer to IUnknown? If so, how do I then get access to the other interfaces. Paul. Quote: > Pass them as IUnknown and dynamically_cast them back to what they were... > > Hi > > I need to transfer a reference to a COM object as a parameter to another > COM > > object in C++. What do I need to implement on both sides? On the 'sender > > side' to allow the object to be passed by reference, and on the 'receiver > > side' what is actually received? > > I can't find any reference on MSDN or on previous newsgroup posts... > > Cheers, > > Paul.
Sun, 23 Nov 2003 19:09:45 GMT

Thomas Hanse #5 / 8	Passing COM objects as parameters to other COM objects Quote: > OK, so is there any sample code around at all? > What I actually need to do is send from Visual Basic Scripting. i.e. I know NOTHING of VB Quote: > Result = MyObject2.MyMethod(MyObject1) > On the C++ receiver side would this actually receive a pointer to IUnknown? Don't know Quote: > If so, how do I then get access to the other interfaces. If it does, you can cast it to the apropriate interface by doing : IMyInterface myInt = dynamic_cast<IUnknown*>(myIncomingPointer); But this is WAY OFF TOPIC at this groupt, consider sending posts about ATL, ActiveX, COM etc... to Quote: > Paul. [snip]
Sun, 23 Nov 2003 19:30:50 GMT

Christian McArdl #6 / 8	Passing COM objects as parameters to other COM objects Quote: > Pass them as IUnknown and dynamically_cast them back to what they were... Um. Don't dynamic cast. Use QueryInterface. You can pass any interface pointer directly. You don't need to send IUnknown only for C++. However, if you are using scripting, then IUnknown it is. In C++, to pass an object into a function, use in idl [in] IUnknown *p as a function parameter. Do not call AddRef or Release on the pointer, either in the calling function or the called, unless the parameter is being saved for future reference. Then it is best to use a smart pointer class, such as CComPtr<> to do it for you. If you are not using scripting, you can replace IUnknown with the interface of your choice so you don't have to bother QueryInterfacing into what you really want. Christian.
Sun, 23 Nov 2003 19:54:42 GMT

S Chapma #7 / 8	Passing COM objects as parameters to other COM objects Paul, I have a similar situation and what i do is as Thomas said on the C++ side receive the object as IUknown* but I then use QueryInterface to get the required interface pointer rather than using dynamic_cast as the former is safer. Quote: > > OK, so is there any sample code around at all? > > What I actually need to do is send from Visual Basic Scripting. i.e. > I know NOTHING of VB > > Result = MyObject2.MyMethod(MyObject1) > > On the C++ receiver side would this actually receive a pointer to > IUnknown? > Don't know > > If so, how do I then get access to the other interfaces. > If it does, you can cast it to the apropriate interface by doing : > IMyInterface myInt = dynamic_cast<IUnknown*>(myIncomingPointer); > But this is WAY OFF TOPIC at this groupt, consider sending posts about ATL, > ActiveX, COM etc... to > > Paul. > [snip]
Mon, 24 Nov 2003 03:13:48 GMT

Peter Partc #8 / 8	Passing COM objects as parameters to other COM objects No I don't think so, script will not like IUnknown. You best pass IDispatch for script (in VB it will be of type Object or variant, in VBScript it would be a variant). ...and I agree with your comment about not using casts....casting an interface pointer parameter (that was not conditioned with iid_is in the IDL prototype) that is a good way to cause an access violation if the pointer is to a proxy. Peter Partch Quote: > > Pass them as IUnknown and dynamically_cast them back to what they were... > Um. Don't dynamic cast. Use QueryInterface. > You can pass any interface pointer directly. You don't need to send IUnknown > only for C++. However, if you are using scripting, then IUnknown it is. > In C++, to pass an object into a function, use in idl > [in] IUnknown *p > as a function parameter. Do not call AddRef or Release on the pointer, > either in the calling function or the called, unless the parameter is being > saved for future reference. Then it is best to use a smart pointer class, > such as CComPtr<> to do it for you. > If you are not using scripting, you can replace IUnknown with the interface > of your choice so you don't have to bother QueryInterfacing into what you > really want. > Christian.
Mon, 24 Nov 2003 21:10:34 GMT

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