Dear Rene
Thank you very much for your detailed answer, it is very helpful for me.
Do you think it would make sense to put this in the User_Guide, e.g.
maybe as a table of objects that you need not create and delete yourself?
Thank you once again.
Best regards
Christian Stratowa
----------------------------------
C.h.r.i.s.t.i.a.n S.t.r.a.t.o.w.a
V.i.e.n.n.a. A.U.S.T.R.I.A
e-mail: cstrato@EUnet.at
Rene Brun wrote:
> Hi Christian,
>
> Sorry for answering only now to your mails.
>
> cstrato@EUnet.at wrote:
> >
> > Dear Rooters
> >
> > I am writing code which I compile as library "Mylib.so". I am used to
> > create
> > my objects with "new obj" and delete them after use with "delete obj".
> >
> > However, when using root, in the following cases I am not sure what to
> > do:
> >
> > 1, "obj = gDirectory->Get("name");":
> > Does this create the object or do I have first to call "obj = new
> > TObject"?
>
> The object is created by Get. You must cast to the expected class.
> MyClass *obj = (MyClass*)gDirectory->Get("name");
>
> > Do I have to call "delete obj" afterwards?
>
> Yes or No. If the object you are reading is a TH1 or TTree, these objects
> are automatically added to the list of objects in memory associated
> to the current directory. When you will close the file, these objects
> will be automatically deleted. Of course, you can delete them before
> closing the file.
> For all the other objects, it is your responsability to delete the
> objects.
>
> >
> > 2, "tree->MakeClass("MyClass");":
> > When I have "tree->Branch("br","ClassA",&classA,64000,0);" and call
> > MakeClass,
> > then the automatically generated code "MyClass.h" uses TTree, TBranch,
> > ClassA
> > without creating any of these classes first.
> > When I use this code in my library code, do I have to create these
> > classes first?
>
> No, the creation of these objects is automatic. See an example of use
> in the comments printed in MyClass.C. Simply do:
> MyClass xx;
> xx.GetEntry(i);
> See MyClass constructor and the function MyClass::Init in MyClass.h.
>
> > At the moment my code creates these classes in a constructor (new TTree,
> > new TBranch,
> > new MyClass) and calls "delete tree, delete br, delete classA" in a
> > destructor.
> >
> > This code works fine, nevertheless my question is:
> > Is this the correct way to do?
>
> I repeat, you do not have to create these objects.
>
> > Do I create a memory leak by doing this?
>
> Probably not. When you close the file containing these objects, they are
> automatically deleted from memory.
>
> > Is it not necessary to create these classes?
> >
> > At last a general question:
> > How can I test whether my code produces memory leaks?
> >
>
> Root has a facility to detect memory leaks by monitoring the number
> of classes created/deleted (see TObjectTable). To use this facility,
> edit the file .rootrc if you have this file or $ROOTSYS/system.rootrc
> and edit/add the two following lines:
> Root.MemStat: 1
> Root.ObjectStat: 1
>
> In your code, for example in your loop where you call tree.GetEntry(i),
> you can insert the line
> gObjectTable->Print();
> This line will print the list of active classes and the number of
> instances
> for each class. By comparing consecutive Prints, you can see objects
> that you forgot to delete.
> Note that this method cannot show leaks coming from the allocation
> of non objects or classes unknown to Root.
>
> Rene Brun
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