Adding a Pre-existing TBranch to TTree

[NSos]

---

ROOT Version: 5
Platform: Scientific Linux 6.10
Compiler: g++ 4.4.7

---

Hi everyone, I am struggling with writing TBranch objects out of a vector into a new tree. More specifically, I am unsure about how one initializes the address of a new TBranch so that when I fill the TTree, a copy of a pre-existing TBranch is written to it. Here is a minimal code to show the problem:

#include <iostream>
#include <TFile.h>
#include <TTree.h>
#include <TBranch.h>
#include <TKey.h>

using namespace std;

int main(){

  int i = 0;
  vector<TBranch*> Detectors;
  
  TFile* data = TFile::Open("Data.root");
  TKey *key = 0;
  TTree* event = 0;
  TBranch* detector = 0;
  TObjArray* branch_list = 0; 
  
  if(data->IsOpen()){
  	
  	TIter next_event(data->GetListOfKeys()); 
    
		while((key = (TKey*)next_event())){
		
		  if(strcmp(key->GetClassName(), "TTree")){
		  
		    continue;
		  }
		  
		  event = (TTree*)data->Get(key->GetName()); 
		  branch_list = event->GetListOfBranches();
		  
		  for(i = 0; i < branch_list->GetEntries(); i++){
		  
		    detector = (TBranch*)branch_list->At(i); 
		    Detectors.push_back(detector);
		  }
		}
  }
  
  else{cout << "ERROR: File failed to open." << endl;}
  
  TFile* rootout = TFile::Open("Test.root", "recreate");
  
  for(i = 0; i < Detectors.size(); i++){
  
    TTree* out_tree;

    //Don't know how to initialize the branch to copy the Detectors[i] branch and associate it with the TTree
    TBranch* out_branch = out_tree->Branch(Detectors[i]->GetName(), &Detectors[i], "data/I"); 
    out_branch = Detectors[i];
    
    out_tree->Fill();
    out_tree->Write();
  }
  
  Detectors.clear();
  
  data->Close();
  rootout->Close();

  return 0;
}

[Wile_E_Coyote]

Try with the TTree::CloneTree method:

grep -r CloneTree ${ROOTSYS}/t[eu]*

[NSos]

I was hoping to add a branch from the vector rather than from the original tree. If I understand correctly, CloneTree method will copy from the original TTree instead.

[pcanal]

Can you clarify your goal? (i.e. where is the data for the ‘vector’ coming from compared to CloneTree)?

[NSos]

Thanks for further interest in the topic. I re-wrote my code and used CloneTree() method and forgot to mark the thread solved. I shall do that now.