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Do i must an AddRef() ?

Posted on 2002-07-30
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Hello

I would like to know if i must do an implicit AddRef() when ADO returns me a Fields collection ....

For instance:

      if( oRS->Open( Source, Conn, adOpenStatic,  adLockPessimistic, adCmdTable ) == 0 )
      {

         // DO I CONSIDER THAT THE AddRef() HAS
         // BEEN MADE BY ADO ? So the only thing i
         // must do is to impliclty call the Release()
         // function.


         CComPtr<Fields15> allfield;
         allfield.Attach( oRS->get_Fields() );


         // OR I DO IT BY ATL CLASS, and the Release()
         // function will be called too.


         CComPtr<Fields15> allfield;
         allfield = oRS->get_Fields();


Is it the same thing for all ADO objects, ie. retrieving an unique field "Field15" ??

Thank you to answer me
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Question by:mars
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peterchen092700 earned 400 total points
ID: 7221171
no, you need not.

Let's first discuss the AddRef/Release rules without  smart pointers (like CComPtr)

* if a function returns an itf ptr, the function addref's before returning, and the caller releases when he is done using it.

* if an itf ptr is passed to a function as parameter, neither the caller nor the function need to addref or release.

* If a function receives a itf ptr as parameter, *and* stores this pointer to use it after the function has returned, it must AddRef the itf ponter, and it must be released when it is no longer used.

------

Smart pointers will do all this handling for you (although they end up with a few more AddRef's and Releases than technically necessary). There are only a few places where you have to be careful:

a) raw interface pointer returned from function
you should use Attach instead of assignment or the Constructor:

IMyInterface * MyFace();
...
CComPtr<IMyInterface> cp;
cp.Attach(MyFace());
// MyFace has called AddRef,
// the ComPtr DTor will call Release,

If you would have used

CComPtr<IMyInterface> cp = MyFace();

there would be "one AddRef to much"

b) passing the address of an itf ptr to a function:
if it's declared
HRESULT Foo(/* [out]*/ IMyInterface ** p)
you can use:

CComPtr<IMyInterface> cp;
hr = Foo(&cp);

However, if it's declared
HRESULT Bar(/* [in,out]*/ IMyInterface ** p)

you need to:

CComPtr<IMyInterface> cp;
IMyInterface * piraw = cp.Detach();
hr = Foo(&cp);
cp.Attach(piraw);

Helped?
Peter
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