TTree GetEntry Uninitialised

[cjt00]

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ROOT Version: 5.34/32
Platform: Not Provided
Compiler: Not Provided

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eventsout.root (353.1 KB)

I want to read a the entries from a ttree. I have a very simple macro to open the file and should print the value of one of the variabes:

#include <TROOT.h>
#include <TChain.h>
#include "TObject.h"
#include "TTree.h"
#include "TBranch.h"

void test(){


  TFile *f = TFile::Open("eventsout.root");

  Double_t x[2];
  TTree *t;
  TBranch *b;

  f->GetObject("treeout",t);

  t->SetBranchAddress("in.t",x,&b);

  Long64_t n =  t->GetEntriesFast();

  // t->Show(10);

  t->GetEntry(10);

 //Long64_t m = t->LoadTree(10);


  std::cout << x[0] << std::endl;

}

The show command displays all the data so clearly the tree is being found ok, but the print statement at the bottom just displays an uninitialised value like 1e-315.

I have tried passing a reference to x in SetBranchAddress:

 t->SetBranchAddress("in.t",&x,&b);

But this does not work either.

I have no idea why this is happening.

I have attached the file I’m reading in.

[Wile_E_Coyote]

If you don’t know how to deal with your tree, see how various flavours of automatically generated “analysis skeletons” deal with it.

[cjt00]

The code above is based on how a skeleton is already doing it which is why I don’t understand why it’s not working.

Here is the treeout class for you.treeout.C (1.4 KB)
treeout.h (45.7 KB)

I need to iterate over a lot of these files to create an array of histograms.

[Wile_E_Coyote]

Well, you did your homework so, here’s a carrot for you:

{
  TFile *f = TFile::Open("eventsout.root");
  if ((!f) || f->IsZombie()) { delete f; return; } // just a precaution
  TTree *t;
  f->GetObject("treeout", t);
  if (!t) { delete f; return; } // just a precaution
  t->SetMakeClass(1); // tree in MakeClass mode
  t->SetBranchStatus("*", 0); // disable all branches
  
  const Int_t kMaxin = 2;
  Int_t in;
  Double_t x[kMaxin]; //[in] (a variable size array)
  
  t->SetBranchStatus("in", 1); // activate branch
  t->SetBranchAddress("in", &in);
  t->SetBranchStatus("in.t", 1); // activate branch
  t->SetBranchAddress("in.t", x);
  
  Long64_t n = t->GetEntries();
  if (n > 10) n = 10; // just the first 10 events
  for (Long64_t i = 0; i < n; i++) {
    t->GetEntry(i);
    std::cout << i << " : " << in << " :";
    if (in > kMaxin)
      { std::cout << " OUCH! WE ARE DOOMED!" << std::endl; break; }
    for(Int_t j = 0; j < in; j++) {
      std::cout << " " << x[j];
    }
    std::cout << std::endl;
  }
  
  // t->ResetBranchAddresses(); // disconnect from local variables
  delete f; // automatically deletes "t", too
}

[cjt00]

That worked thanks!

Have you any idea what was wrong with my code?