tcl.C File Reference

Detailed Description

How to write a TClonesArray to a TTree

The following tests can be run Interactive tests

Root > .x tcl.C        //no-split interpreted
Root > .x tcl.C(1)     //split    interpreted
Root > .x tcl.C++      //no-split compiled
Root > .x tcl.C++(1)   //split    compiled

Batch tests: same as above but with no graphics

root -b -q tcl.C
root -b -q tcl.C++
root -b -q "tcl.C(1)"
root -b -q "tcl.C++(1)"

#include "TFile.h"
#include "TClonesArray.h"
#include "TH2.h"
#include "TLine.h"
#include "TTree.h"
#include "TBenchmark.h"
#include "TRandom.h"

void tclwrite(Int_t split)
{
// Generate a Tree with a TClonesArray
// The array can be split or not
   TFile f("tcl.root","recreate");
   f.SetCompressionLevel(1); //try level 2 also
   TTree T("T","test tcl");
   TClonesArray *arr = new TClonesArray("TLine");
   TClonesArray &ar = *arr;
   T.Branch("tcl",&arr,256000,split);
   //By default a TClonesArray is created with its BypassStreamer bit set.
   //However, because TLine has a custom Streamer, this bit was reset
   //by TTree::Branch above. We set again this bit because the current
   //version of TLine uses the automatic Streamer.
   //BypassingStreamer saves space and time.
   arr->BypassStreamer();
   for (Int_t ev=0;ev<10000;ev++) {
      ar.Clear();
      Int_t nlines = Int_t(gRandom->Gaus(50,10));
      if(nlines < 0) nlines = 1;
      for (Int_t i=0;i<nlines;i++) {
         Float_t x1 = gRandom->Rndm();
         Float_t y1 = gRandom->Rndm();
         Float_t x2 = gRandom->Rndm();
         Float_t y2 = gRandom->Rndm();
         new(ar[i]) TLine(x1,y1,x2,y2);
      }
      T.Fill();
   }
   T.Print();
   T.Write();
}

void tclread()
{
// read file generated by tclwrite
// loop on all entries.
// histogram center of lines
   TFile *f = new TFile("tcl.root");
   TTree *T = (TTree*)f->Get("T");
   TH2F *h2 = new TH2F("h2","center of lines",40,0,1,40,0,1);

   TClonesArray *arr = new TClonesArray("TLine");
   T->GetBranch("tcl")->SetAutoDelete(kFALSE);
   T->SetBranchAddress("tcl",&arr);
   Long64_t nentries = T->GetEntries();
   for (Long64_t ev=0;ev<nentries;ev++) {
      arr->Clear();
      T->GetEntry(ev);
      Int_t nlines = arr->GetEntriesFast();
      for (Int_t i=0;i<nlines;i++) {
         TLine *line = (TLine*)arr->At(i);
         h2->Fill(0.5*(line->GetX1()+line->GetX2()), 0.5*(line->GetY1()+line->GetY2()));
      }
   }
   h2->Draw("lego");
}

void tcl(Int_t split=0)
{
   gBenchmark->Start("tcl");
   tclwrite(split);
   tclread();
   gBenchmark->Show("tcl");
}

Author

Rene Brun

Definition in file tcl.C.