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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