dimuon/convert_root_to_txt.cxx

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#include <iostream>
 
void extract_trkindex(){
  TChain *chain = new TChain("infmom");
  chain->Add("temp/*.root");
  ofstream out;
  TString para_file_name("dimu.txt");
  out.open(para_file_name,ios::out);
  long m_run, m_event, m_trk;
  chain->SetBranchAddress("run", &m_run);
  chain->SetBranchAddress("event", &m_event);
  chain->SetBranchAddress("trkindex", &m_trk);
 
  long m_num_evt = chain->GetEntries();
  long m_scale = m_num_evt/100000;
  if(!(m_scale%2)) m_scale --;
  for(long i=0; i<m_num_evt; i++){
    if(i%10000==0)  cout << "i=" << i  << endl;
    if(i%m_scale!=0) continue; 
    chain->GetEntry(i);
    out << m_run << "   " << m_event << "   " << m_trk << endl;    
  }
  cout << "the scale is: " << m_scale << endl;
  out.close();
}