Hi Davide,
When a branch contains a TRef, the branch referenced by the TRef
is not read automatically (that is the main idea behind TRef).
It is up to you to test if the referenced object is there (GetObject
non null) and if it is null, you must call GetEntry for
the corresponding branch (as you show in your example).
We will add in a future version, the possibility to load
automatically the referenced branch when the TRef object
is dereferenced. This feature is for example necessary
in the tree viewer.
Rene Brun
On Fri, 22 Nov 2002, Davide Grandi wrote:
> Hi rooters,
> I have a problem with TRef and TRefArrays.
> I'm using root version 3.03.09
> on a Linux machine, Intel 2.0 Ghz double processor
>
> I'm reading events written with in a tree with branches that
> are TClonesArray and include TRef, TRefArrays, with
> TRef pointing from one branch as for example fParticle
>
> TClonesArray* fParticle offset= 0 type=64
>
> to another as for example fTrack
>
> TClonesArray* fTrack offset= 0 type=64
>
> so that in class Paricle there is
>
> StreamerInfo for class: Particle, version=1
> BASE TObject offset= 0 type=66 Basic ROOT object
> int Particle offset= 0 type= 3
> TRef fTrack offset= 0 type=61 pointer to track;
> ....
> ..
> .
> ..
> .
>
> StreamerInfo for class: Track, version=1
> BASE TObject offset= 0 type=66 Basic ROOT object
> int Status offset= 0 type= 3
> int Pattern offset= 0 type= 3
> int Address offset= 0 type= 3
> ...
> ..
> ..
>
> suppose that in my selection code I want to use the reference TRef fTrack
> to the object (class) Track, can I get it without loading the respective
> branch b_Track? I mean in this example(1) of the code
>
>
>
> example(1):
> -----------------------------------------------------------------------
>
> b_Particle->GetEntry(entry);
>
> if(Particle->GetSize()>0){
> pobj=Particle->At(0);
> Particle* p_ok=dynamic_cast<Particle*>(pobj);
>
> if(p_ok){
> cout << p_ok->fTrack.GetObject() << endl;
> }
> }
>
> ----------------------------------------------------------------------
> I got (nil) pointers while in this example(2) of code
>
> example(2)
>
> ---------------------------------------------------------------------
> b_Particle->GetEntry(entry);
>
> if(Particle->GetSize()>0){
> pobj=Particle->At(0);
> Particle* p_ok=dynamic_cast<Particle*>(pobj);
>
> if(p_ok){
> b_Track->GetEntry(entry);
> cout << p_ok->fTrack.GetObject() << endl;
> }
> }
> ---------------------------------------------------------------------
> I got the pointers..
>
> is it possible to do it (get the pointers) without loading the branch
> b_Track (or better loading the branch only when is needed to access the
> data, in the relative if cycle)?
> I hope this is not a stupid question....
>
> Thanks
>
> Davide
>
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