Alexander Yuryevich Zvyagin writes:
> Dear ROOTers,
>
> I'd like to discuss one feature of the TH1 class: how the member function
> void TH1::Build() works. (You'll find the function body at the end of this
> E-mail.) This function is called when TH1 constructor is invoked.
>
> // Example 1.
> TH1F a("E",....), b("E",....);
>
> This is *good* C++ code and this is *bad* ROOT code.
> What will ROOT do?
> The histogram a("E",...) is created and added
> (See TObject::AppendDirectory()) to the current directory. On default it
> is gDirectory. OK, you have histogram 'a'. Then ROOT will try to create
> histogram b("E",...) with the *same* name "E" as the histogram 'a' has.
> ROOT will find that object with the same name already exists in the
> gDirectory and it'll try to *delete* it.
this is half-true: in this case ROOT will delete `a' from the list
of existing histograms but not necessarily it will e trying to delete
the object itself.
>
> So ROOT will delete pointer to
> statically allocated object. Something like this:
> {
> int a;
> int *b = &a;
> delete b;
> }
> This is bad thing. Your *good* C++ code will crash. I think this is
> ROOT bug.
Yes, this is a bad thing to do so as far as I understand (please
correct me if I'm wrong here) ROOT doesn't do it:
TObjects in ROOT containers "know" if they were allocated statically
or on the heap. Any TSequence(TList, TObjArray etc)::Delete method
deletes only those allocated on the heap.
Regards, pasha.
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