Read a TTree from a root file

[naikal_mc]

Hello ROOT experts,
I am trying to read a tree “reco” from a file.root.
I am using the script beneath:

#include "TFile.h
#include "TH1F.h
#include "TTreeReader.h
#include "TTreeReaderValue.h

{
TH1F *h1 = new TH1F(“h1”, “h1 title”, 1000, -100, 100);

TFile *myFile = TFile::Open("$ROOTSYS/macros/crazy.10.root");
TTreeReader reader(“reco”, &myfile);

TTreeReaderValue<Float_t> llratio(reader, “llratio”);
TTreeReaderValue<Float_t> llratioE(reader, “llratioE”);
TTreeReaderValue<Float_t> enew(reader, “enew”);

TH1F *hpx = new TH1F(“hpx”,“px distribution”,100,-3,3);

TH2F *hpxpy = new TH2F(“hpxpy”,“py vs px”,30,-3,3,30,-3,3);

while (reader.Next()) {
h1->Fill(*enew + *llratio);
}

h1->Draw();

}

But root isn’t drawing the histogram. What am I doing wrong? :\

[Danilo]

Hi,

I assume this is a macro and not a program you compiled.
Most likely the issue is that the histogram is being drawn but immediately deleted after leaving the scope. You can draw a clone of the histogram (DrawClone()) in order to have the painted entity survive the scope.

Cheers,
D