TTree and GetV1, limit in number of entries

From: Andrea Massironi <Andrea.Massironi_at_cern.ch>
Date: Fri, 2 Dec 2011 19:01:25 +0100

Dear ROOTers,

     I have a problem with the use of the method "GetV1()" of the class TTree.
It seems that it returns at most 1M entries.

Example code:

    TTree tree("tree","tree");
    double var1;
    tree.Branch("var1",&var1,"var1/D");

    for (int i=0; i<3000000; i++){ var1 = 1.; tree.Fill();}

    tree.Draw("var1","","goff");
    Double_t *vect1 = tree.GetV1();

    int nEntries = tree.GetEntries();
    for (int iEntry = 0; iEntry<nEntries; iEntry++){

      if (!(iEntry%100000)) {
       std::cout << "v1[" << iEntry << "] = " << vect1[iEntry] << " 
    ---  " << std::endl ;
      }

    }

Output:

    v1[0] = 1 ---
    v1[100000] = 1 ---
    ...

    v1[900000] = 1  ---
    v1[1000000] = 0  ---
    v1[1100000] = 5.94459e-312  ---
    v1[1200000] = 3.63742e+233  ---
      *** Break *** segmentation violation

Is there a workaround to deal with this apparent limitation?

Thanks,

     Andrea Received on Fri Dec 02 2011 - 19:00:57 CET