Re: Problem with TObjArray

Rene Brun (Rene.Brun@cern.ch)
Sun, 01 Nov 1998 09:38:22 +0100

Hi Alexander,
This is not a bug.
TObjArray is a TCollection. See documentation of TObject::Write
and TCollection::Write.
By default, all objects in the collection are written individually
(each object generates its own key). To write all objects using one key
specify a name and set option to kSingleKey (i.e 1).

Rene Brun

Alexander Zvyagin wrote:
>
> IHEP, Protvino, Russia, 1-NOV-1998
>
> Dear ROOTers and ROOT developers,
>
> I have problem in storing TObjArray into ROOT file under ROOT 2.00/12. The
> macro is very simple, I try to save TObjArray in ROOT file, then read it back,
> and test what have I read. Macro and it output is attached below.
>
> Thanks in advance,
> Alexander.
>
> void bug(void)
> {
> printf("Example 1: Storing TObjArray with 0 entries.\n");
>
> f1 = new TFile("f.root","RECREATE");
> o1 = new TObjArray;
> f1 -> ls();
> o1 -> Write("o1");
> f1 -> ls();
> f1 -> Close();
>
> printf("---------\n");
>
> // Reding back.
>
> f1 = new TFile("f.root");
> f1 ->ls();
> o1 = (TObjArray*)f1->Get("o1");
> if( NULL==o1 )
> printf("Can not find object\n");
> else
> printf("Entries = %d\n",o1 -> GetEntries());
>
> printf("===================================\n");
>
> printf("Example 2: Storing TObjArray with four entries.\n");
>
> f1 = new TFile("f.root","RECREATE");
> o1 = new TObjArray;
> o1 -> Add(new TObject);
> o1 -> Add(new TObject);
> o1 -> Add(new TObject);
> o1 -> Add(new TObject);
> printf("Entries = %d\n",o1 -> GetEntries());
> f1 -> ls();
> o1 -> Write("o1");
> f1 -> ls();
> f1 -> Close();
>
> printf("---------\n");
>
> // Reading back.
>
> f1 = new TFile("f.root");
> f1 ->ls();
> o1 = (TObjArray*)f1->Get("o1");
> if( NULL==o1 )
> printf("Can not find object\n");
> else
> printf("Entries = %d\n",o1 -> GetEntries());
>
> printf("===================================\n");
> }
>
> Output:
> root [0] .x bug.C
> TFile** f.root
> TFile* f.root
> TFile** f.root
> TFile* f.root
> ---------
> TFile** f.root
> TFile* f.root
> Can not find object
> ===================================
> Entries = 4
> TFile** f.root
> TFile* f.root
> TFile** f.root
> TFile* f.root
> KEY: TObject o1;2 Basic ROOT object
> KEY: TObject o1;2 Basic ROOT object
> KEY: TObject o1;2 Basic ROOT object
> KEY: TObject o1;1 Basic ROOT object
> ---------
> TFile** f.root
> TFile* f.root
> KEY: TObject o1;2 Basic ROOT object
> KEY: TObject o1;2 Basic ROOT object
> KEY: TObject o1;2 Basic ROOT object
> KEY: TObject o1;1 Basic ROOT object
> Entries = 0
> ===================================
> NULL
> root [1] .q