Error saving a tree into a root file

ROOT
1

Hello,

I am a new root user and I am trying to store in a rootfile (“doesnotwork.root”) some events selected from another rootfile (whose path is “FILENAME”).
I can create the output one and make root write the tree (t3) into it, because when I try to open the rootfile via Tbrowser I find my variables (“e” and “time”), but if I try to see an histogramme of the contents of one of these two variables I get this error so many times:
Error in TFile::ReadBuffer: error reading all requested bytes from file doesnotwork.root, got 0 of 1919

I’ve tried everything I know, someone please help me out.

Thanks
Guido

 // --------------------------------------------------------------------------
  // Open rootfile and get # of events
  // --------------------------------------------------------------------------
  TFile *f=new TFile("doesnotwork.root","RECREATE"); // there I will write the result of the selection
  TFile *rootfile=new TFile(FILENAME,"UPDATE"); // from here I load data
  if (!(rootfile->IsOpen())){ 
    printf("I had trouble opening the rootfile.\n");
    printf("I'm sorry, but I have to terminate here.\n");
    exit(EXIT_FAILURE);
  }
  // go to folder
  gDirectory->cd("PROD2NTU");
  // go to tree
  TTree *alberello;
  gDirectory->GetObject("h1;1",alberello);
  NEVENTI = alberello->GetEntries();
  cout << "In " << FILENAME << " sono registrati " << NEVENTI << "eventi." << endl;
  gDirectory->pwd();

  // some code ….

///*--------------------------------------------------------------- needs debugging
  // make a new TTree to organize data of interesting tracks
  TTree *t3=new TTree("t3","A nice TTree");
  Float_t e,time;
  TBranch *br1 = t3->Branch("e",&e,"e/F");
  TBranch *br2 = t3->Branch("time",&time,"time/F");
//*/

  for(i=0;i<NEVENTI;i++){
    alberello->GetEntry(i);
    // some other code... 
    	if(crystal[evento.cry[k]]==1){ // if track hits the crystal which gave a signal add the signal to histogramme 
	  //* ------------------------------------- needs debugging
	  e=(Float_t)evento.e[k];
	  time=(Float_t)evento.time[k];
	  t3->Fill();
	  // cout << "e vale " << e << " time vale " << time << endl; // DEBUG
	  //*/
	  if(evento.time[k]>1500 && evento.time[k]<2500){ // cut on TDC counts 
	    hADC->Fill(evento.e[k]);
	    hTDC->Fill(evento.time[k]);
	  }
  }
}

  padup->cd();
  hADC->Draw();
  hADC->Write();
  paddown->cd();
  hTDC->Draw();
  hTDC->Write();
  ///* ------------------------------------------------------- needs debugging
  f->cd();
  gDirectory->pwd();  
  t3->Write();
  f->Close();
  //*/
2

Try to add:
f->cd();
right before:
TTree *t3=new TTree(“t3”,“A nice TTree”);
Also, instead of “f->Close();” you can simply use "delete f;"
BTW. Why do you open the “rootfile” in the “UPDATE” mode if you just retrieve objects from it?

3

First of all thank you very much for your reply.

About what you suggested, I just tried with

[quote]Try to add:
f->cd();
right before:
TTree *t3=new TTree(“t3”,“A nice TTree”);[/quote]

and it works!
I had already tried “delete f;”, but it still didn’t work

Actually I open my source rootfile in UPDATE mode because I need to attach a couple of histogrammes, but that’s not essential. So, to me, the problem is solved. But if I wanted to add those histogrammes also, I wouldn’t know how to do… Anyway thank you again! =D>

Guido

4

Try: // ... TDirectory *oldDir = gDirectory; // save the current directory f->cd(); // switch to "f" for "t3" creation TTree *t3 = new TTree("t3", "A nice TTree"); gDirectory = oldDir; // restore the saved directory // ...