TChain and TEntryList

From: Andrea Massironi <andrea.massironi_at_cern.ch>
Date: Mon, 25 Oct 2010 23:40:11 +0200

Dear Rooters,

    I found a strange behaviour about TChain and TEntryList.

I first create a simple TTree

    TFile file("out.root","RECREATE");
    TTree myTree("myTree","myTree");
    int a;
    myTree.Branch("a",&a,"a/I");
    a = 10;
    for (int i=0; i<100; i++) { a = i; myTree.Fill();}     myTree.Write();

In two different files (that is simply changing out.root -> out2.root). Then if I read one tree using a TChain

    TChain chain("myTree");
    chain.Add("out.root");
    chain.Draw(">>myList","a<10","entrylist");     TEntryList *myList = (TEntryList*)gDirectory->Get("myList");     myList->GetLists()

The "GetLists()" returns 0x0.
While if I simply do

    TChain chain("myTree");

    chain.Add("out.root");
    chain.Add("out2.root");
    chain.Draw(">>myList","a<10","entrylist");

    TEntryList *myList = (TEntryList*)gDirectory->Get("myList");     myList->GetLists()

It works well, and I can do, for example

    myList->GetLists()->GetEntries()

and I get "2" as expected.
If this behaviour expected? I would have expected to get one single list in case of adding one file, and 2 lists in case of 2.

I'm working with 5.27/07 trunk_at_35856; but I found the very same problem with 5.22/00d.
The problem was triggered by https://savannah.cern.ch/bugs/?60569 and the work-around.

Thanks,

     Andrea Received on Mon Oct 25 2010 - 23:40:25 CEST