Hi Thomas,
Since the introduction of the new branch style (TBranchElement), the default
in versions 3.01 and 3.02, SetAutoDelete is not required anymore and it
is ignored. This process is now automatic.
Suppose you have a branch with
MyClass *MyObject = 0;
tree.SetBranchAddress("bname",&MyObject);
When calling tree.GetEntry(), if MyObject is null, a new instance of MyClass
is created, otherwise the previous object is replaced by the new data.
If MyObject has pointers to other objects (may be collections),
these objects are automatically deleted recreated and filled with the new data.
If MyClass contains only basic types or objects that in turn contain only basic
types, no constructors need to be called-> an appreciable gain in time.
In your loop calling GetEntry, you can add a statement
delete MyObject; MyObject = 0;
to force a call to your destructor. If GetEntry finds a null pointer, it will
automatically call the default MyClass constructor.
In case of TChains, SetAutoDelete was never taken into account.
I did not implement it for the new branch styles since it is redundant.
Rene Brun
Thomas Bretz wrote:
>
> Hi Rene,
>
> if I understood you correctly code like :
> ----------
> TFile file(...);
> MyObj *myobjptr = new MyObj;
> file->Get("Tree")->GetBranch("branch")->SetAutoDelete();
> file->Get("Tree")->GetBranch("branch")->SetAdress(&myobjectptr);
> for (int i=0; i<100; i++) file->Get("Tree")->GetEntry(i);
> ----------
> should result in a call to ~MyObj every time a new event is read. But in
> my case SetAutoDelete is completely ignored:
> ----------
> TChain chain("Tree");
> chain.Add("file.root");
> MyObj *myobjptr = new MyObj;
> chain.GetBranch("branch")->SetAutoDelete();
> chain.SetBranchAddress("branch", &myobjectptr);
> for (int i=0; i<100; i++) chain.GetEntry(i);
> ----------
> does only result in _one_ call to the destructor of MyObj. That's the
> problem.
>
> In my opinion the problem is due to the fact that when LoadTree switches
> files (also from no file to the first file) the information stored in
> TBranch (set via TBranch::SetAutoDelete()) is lost. Maybe I'm wrong.
>
> Thomas.
>
> > > I'm using a TChain to access my tree and its branches. I was wondering,
> > > why the destructors of my functions are not called independant of the
> > > Setting of TChain::GetBranch->SetAutoDelete. From a look at the code of
> > > TChain::GetEntry/LoadTree it seems to me, that the setting of the
> > > autodelete flag is skipped at least when a new File is opened and the
> > > TChainElement settings are copied to the TBranch of the new file. Am I
> > > right, or was the way of setting these flag incorrect?
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