Re: How to get an Histogram ?

Hi Jordi,

I am not sure about your issue as I don't know what exactly you are trying to achieve. However after simplifying your example macro I found two errors:

{
  int N = 2;
  TString parnames[N] = { "QCDnorm_corr_mu", "QCDnorm_corr_mu_btag"};

  TFile *file = TFile::Open("PSE/JO_muon_PSE_RbFree/sumRootFile.root");   TTree* HangingTree = (TTree*) file->Get("HangingTree");

  for(int i=0; i<N;i++){
    TString raw = parnames[i];
// here the histograms get overwritten by subsequent calls to Draw()
    HangingTree->Draw(raw+">>histo");
// this line does multiple declaration of h as the loop proceeds
// this is not correct C++ but might be forgivable in CINT, not sure
    TH1D *h = (TH1D*) gROOT->FindObject("histo");     std::cout << raw << " " << h->GetMean() << std::endl;   }
}

I hope this helps.

-- 
Suvayu

Open source is the future. It sets us free.