Question concerning ownership + garbagecollection

ROOT
1

Dear Rooters,

I observed something that i do not understand:
When I have executed the following lines in cint and
want to exit it gives me a segmentation fault

TH1D h;
TFile f(“test.root”, “recreate” );
h.SetName(“test”);
h.SetDirectory( &f );
f.Write();
f.ls();
f.Close();

Am I not supposed to be able to change the directory
of a Histogram after creating it ?

The histogram gets delete at the f.Close(), as it should be,
but after that it seems that some garbagecollection wants
to delete it again.

thanks for any replies
Michael

2

Just move the statement “TH!f h” after the craetion of TFile.
Histograms are created in teh current directory.

Rene

3

[quote=“brun”]Just move the statement “TH!f h” after the craetion of TFile.
Histograms are created in teh current directory.

Rene[/quote]

Hi Rene,
thank you for the fast answer.
I used to do it as you said, the code I sent
was only meant as an example.
Nevertheless: am I right that it should work
in principle ?

What I really would like to do is the following

// does not crash, but histograms do not
// get written to the file
// or with the SetDirectory statements
// crashes at exit

TFile *f = new TFile(“test.root”, “recreate” );
f->cd();
TH1D *h;

// with or without the constructor parameters
// seems anyway that cint ignores them
// but i tried also with a compiler
h = new TH1D[2](“t”, “t”, 1, 0, 1 );
h[0]->SetName(“t1”);
h[1]->SetName(“t2”);

f->ls();
// they were not created in the
// current directory, although I
// expected it

h[0]->SetDirectory( &f );
h[1]->SetDirectory( &f );
f->ls();
//now they are in the current directory

f->Write();
f->Close();

sorry for using your time
Michael

4

What you do is illegal C++. Do something like:

TFile *f = new TFile(“test.root”, “recreate” );
TH1D *h[2];
h[0] = new TH1D(“t1”,“t1”,1,0,1)
h[1] = new TH1D(“t2”,“t2”,1,0,1)
f->Write()

Rene

5

Hi Rene,
thanks for your really fast help.
It works fine as you said.
I still did not quite understand why
the other thing was wrong :unamused:
but since it works …

thanks again + best wishes
Michael

6

Michael,

In your code, you had several invalid statements;

====
TH1D *h;
h = new TH1D[2](“t”, “t”, 1, 0, 1 );

and
h[0]->SetDirectory( &f );
must be:
h[0]->SetDirectory(f);

Rene