access_tree.C

R__LOAD_LIBRARY(libeicsmear);

void access_tree(){

  //Event Class
  erhic::EventPythia *event(NULL); //Note that I use Pointer

  //Particle Class
  erhic::ParticleMC *particle(NULL); //Also use Pointer
  
  //Load ROOT File
  TFile *f = new TFile("../pythia/outfiles/ep_10_100_norad.root");

  //Get EICTree Tree
  TTree *tree = (TTree*)f->Get("EICTree");

  Int_t nEntries = tree->GetEntries();
  cout<<"-------------------------------"<<endl;
  cout<<"Total Number of Events = "<<nEntries<<endl<<endl;

  //Access event Branch
  tree->SetBranchAddress("event",&event); //Note &event, even with event being a pointer

  //Define Some Variables
  Float_t Q2(0);
  Int_t nParticles(0);
  Float_t Eta[500];
  Float_t Px[500];
  Int_t Status[500];
  Int_t id[500];
  
  //Loop Over Events
  for(Int_t i=0;i<10;i++){
    
    tree->GetEntry(i);

    //Write Out Q2
    Q2 = (Float_t) event->GetQ2(); //Can also do event->QSquared
    printf("For Event %d, Q^2 = %.3f GeV^2!\n",i,Q2);
    
    //Get Total Number of Particles
    nParticles = event->GetNTracks();
    printf("For Event %d, we have %d particles!\n",i,nParticles);
    
    //Loop Over Each Particle
    for(Int_t j=0;j<nParticles;j++){
      
      particle = event->GetTrack(j);
      Eta[j] =  (Float_t) particle->GetEta();
      Px[j] = (Float_t) particle->GetPx();
      Status[j] = (Int_t) particle->GetStatus(); //Can also do particle->KS
      id[j] = (Int_t) particle->Id();
      
      if(Status[j]==1){
	printf("For Event %d, particle %d Eta = %.3f!\n",i,j,Eta[j]);
	printf("For Event %d, particle %d Px = %.3f GeV/c!\n",i,j,Px[j]);
	printf("For Event %d, particle %d Status = %d!\n",i,j,Status[j]);
	printf("For Event %d, particle %d Id = %d!\n",i,j,id[j]); 
      }

    }
    
  }

  cout<<"-------------------------------"<<endl;

}