Reading hist from a TTree

Newbie
1

I have a root file named “filename.root” with the tree named “treename”. There is a histogram named “histname” in this tree. I am trying to read this histogram but nothing is showing up. Please let me know my error. Here’s my code.

void TFileRead()
{
        TFile *filename = new TFile("filename.root", "READ"); //READ
        TTree *treename = (TTree*)filename->Get("treename");

//      TH1F* histname = (TH1F*)treename->GetHistogram("histname");

        treename->Draw("histname");
        treename->GetHistogram();
}
2

Can you give more details ? Which error message do you get ? May be post the file filename.root here ?

3

Hi Couet, here are the all the files. Thank you.

filename.root (6.7 KB)
TFileCreate.C (469 Bytes)
TFileRead.C (306 Bytes)

4

histname is not in the tree. It seats in the root file. Simply do:

% root filename.root 
   ------------------------------------------------------------------
  | Welcome to ROOT 6.25/01                        https://root.cern |
  | (c) 1995-2021, The ROOT Team; conception: R. Brun, F. Rademakers |
  | Built for macosx64 on Jul 05 2021, 04:58:33                      |
  | From heads/master@v6-25-01-1526-g96258cd49b                      |
  | With Apple clang version 12.0.5 (clang-1205.0.22.11)             |
  | Try '.help', '.demo', '.license', '.credits', '.quit'/'.q'       |
   ------------------------------------------------------------------

root [0] 
Attaching file filename.root as _file0...
(TFile *) 0x7fb08e33a170
root [1] _file0->ls()
TFile**		filename.root	
 TFile*		filename.root	
  KEY: TTree	treename;1	treetitle
  KEY: TH1F	histname;1	histtitle
root [2] histname->Draw()
1 Like