read_ntuple_with_chain.C

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// Read several previously produced N-Tuples and print on screen its
// content.
//
// you can easily create some files with the following statement:
//
// for i in 0 1 2 3 4 5; \\
// do root -x -b -q \\
// "write_ntuple_to_file.cxx \\
// (\"conductivity_experiment_${i}.root\", 100)"; \\
//  done
 
void read_ntuple_with_chain(){
   // initiate a TChain with the name of the TTree to be processed
   TChain in_chain("cond_data");
   in_chain.Add("conductivity_experiment*.root"); // add files,
                                                  // wildcards work
 
   // define variables and assign them to the corresponding branches
   float pot, cur, temp, pres;
   in_chain.SetBranchAddress("Potential", &pot);
   in_chain.SetBranchAddress("Current", &cur);
   in_chain.SetBranchAddress("Temperature", &temp);
   in_chain.SetBranchAddress("Pressure", &pres);
 
   cout << "Potential\tCurrent\tTemperature\tPressure\n";
   for (size_t irow=0; irow<in_chain.GetEntries(); ++irow){
      in_chain.GetEntry(irow); // loads all variables that have
                                    // been connected to branches
      cout << pot << "\t" << cur << "\t" << temp <<
                          "\t" << pres << endl;
   }
}