Hi Rene,
I don't want to look bothering and annoying, but it seems I have to.
As usual, I got no answer to my question, and I gonna repeat it
literally:
I can't really understand why is this difference in approaches, does
it really must be like that? Can't we make the behavior more uniform
across split and non-split branches?
I mean that I really really would like to have GetEntry() to set the
pointer which was passed to the branch with SetAddress(), no matter it
is split or non-split branch.
As for your receipt below - we really do not know the true type of the
object when we are reading it. ROOT does know, because all the
information is in the trees/branches. I understand that knowing the name
of the class I can create the instance, now how can I get the name of
the class which is in the branch? Do you have some mechanism in ROOT to
accomplish something like this : "knowing TTree and branch name I want
to obtain the class of the object in this branch"? Looking at the
documentation and the code I can't seem to find the relatively easy way
to do it, which will not depend on the details of implementation of your
stuff, or can I?
Cheers,
Andy.
----- Original Message -----
From: Rene Brun <Rene.Brun@cern.ch>
To: Andrei Salnikov <salnikov@SLAC.Stanford.EDU>
Cc: ROOTTALK <roottalk@hpsalo.cern.ch>
Sent: Wednesday, September 15, 1999 8:36 AM
Subject: Re: split/non-split difference in SetAddress()
> Hi Andy,
> I appreciate the fact that you have been able to understand very
deeply
> the way the Tree/Branch mechanism works. Your analysis is perfectly
> correct.
> Now back to your question.
> You can have a perfectly symmetric mechanism between split and
non-plit
> mode
> if instead of:
> ClassBaseA* theObjectPointer_ = 0;
> (ie letting Root instantiate the object itself)
> you make yourself an instance of the object.
> I understand your argument about schema evolution and that you do not
> know
> a priori (I assume at compilation time) what your current class
derived
> from ClassBaseA will be. However, I assume that you must have a
> mechanism
> at run time to find out if you have a ClassA_001 or a ClassA_00N .
> With Root you can create an instance of an object by knowing only
> its class name, say "ClassA__003". Proceed as follows:
> - Get a pointer to the Root TClass object (RTTI) for this class
> TClass *cl = gROOT->GetClass("ClassA_003");
> - Create an instance of the object with:
> ClassBaseA* theObjectPointer_ = (ClassBaseA*)cl->New();
> - Now you can set the branch address
> theBranch_ -> SetAddress ( (void*)(&theObjectPointer_) ) ;
>
> When the object already exists, Root input in split mode will not
> destroy
> the already existing object, theObjectPointer will always have the
same
> value.
> In non-split mode, we have no choice but to delete the previous object
> at the branch address because the new object has not the same size
than
> the previous object in general.
>
>
> Rene Brun
>
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