tree108_tree.C

Go to the documentation of this file.

/// \file
/// \ingroup tutorial_tree
/// \notebook -nodraw
/// This example writes a tree with objects of the class Event.
/// It is a simplified version of $ROOTSYS/test/MainEvent.cxx to
/// write the tree, and $ROOTSYS/test/eventb.C
/// It shows:
///   - how to fill a Tree with an event class containing these data members:
/// ~~~
///     char           fType[20];
///     Int_t          fNtrack;
///     Int_t          fNseg;
///     Int_t          fNvertex;
///     UInt_t         fFlag;
///     Float_t        fTemperature;
///     EventHeader    fEvtHdr;
///     TClonesArray  *fTracks;            //->
///     TH1F          *fH;                 //->
///     Int_t          fMeasures[10];
///     Float_t        fMatrix[4][4];
///     Float_t       *fClosestDistance;   //[fNvertex]
/// ~~~
///   - the difference in splitting or not splitting a branch
///   - how to read selected branches of the tree, and print the first entry with less than 587 tracks.
///   - how to browse and analyze the Tree via the TBrowser and TTreeViewer
///
/// This example can be run in many different ways:
///  - way1 using the Cling interpreter:
/// ~~~
/// .x tree108_tree.C
/// ~~~
///  - way2 using the Cling interpreter:
/// ~~~
/// .L tree108_tree.C
/// tree108_tree()
/// ~~~
///  - way3 using ACLIC:
/// ~~~
/// .L ../test/libEvent.so
/// .x tree108_tree.C++
/// ~~~
/// One can also run the write and read parts in two separate sessions.
/// For example following one of the sessions above, one can start the session:
/// ~~~
///   .L tree108_tree.C
///   tree108_read();
/// ~~~
/// \macro_code
///
/// \author Rene Brun
 
#ifdef R__WIN32
R__LOAD_LIBRARY($ROOTSYS/test/libEvent.dll)
#else
R__LOAD_LIBRARY($ROOTSYS/test/libEvent.so)
#endif
 
#include "TFile.h"
#include "TTree.h"
#include "TBrowser.h"
#include "TH2.h"
#include "TRandom.h"
#include "TClassTable.h"
#include "TSystem.h"
#include "TROOT.h"
#include "../test/Event.h"
 
void tree108_write()
{
   // create a Tree file tree108.root
   TFile f("tree108.root","RECREATE");
 
   // create a ROOT Tree
   TTree t4("t4","A Tree with Events");
 
   // create a pointer to an Event object
   Event *event = new Event();
 
   // create two branches, split one.
   t4.Branch("event_split", &event,16000,99);
   t4.Branch("event_not_split", &event,16000,0);
 
   // a local variable for the event type
   char etype[20];
 
   // fill the tree
   for (Int_t ev = 0; ev < 100; ev++) {
      Float_t sigmat, sigmas;
      gRandom->Rannor(sigmat, sigmas);
      Int_t ntrack = Int_t(600 + 600 * sigmat / 120.);
      Float_t random = gRandom->Rndm(1);
      sprintf(etype, "type%d", ev%5);
      event->SetType(etype);
      event->SetHeader(ev, 200, 960312, random);
      event->SetNseg(Int_t(10 * ntrack + 20 * sigmas));
      event->SetNvertex(Int_t(1 + 20 * gRandom->Rndm()));
      event->SetFlag(UInt_t(random + 0.5));
      event->SetTemperature(random + 20.);
 
      for (UChar_t m = 0; m < 10; m++) {
         event->SetMeasure(m, Int_t(gRandom->Gaus(m, m + 1)));
      }
 
      // fill the matrix
      for (UChar_t i0 = 0; i0 < 4; i0++) {
         for(UChar_t i1 = 0; i1 < 4; i1++) {
            event->SetMatrix(i0, i1, gRandom->Gaus(i0 * i1, 1));
         }
      }
 
      // Create and fill the Track objects
      for (Int_t t = 0; t < ntrack; t++) event->AddTrack(random);
 
      // Fill the tree
      t4.Fill();
 
      // Clear the event before reloading it
      event->Clear();
   }
   // Write the file header
   f.Write();
 
   // Print the tree contents
   t4.Print();
}
 
 
void tree108_read()
{
   // read the tree generated with tree108_write
 
   // note that we create the TFile and TTree objects on the heap !
   // because we want to keep these objects alive when we leave this function.
   auto f = TFile::Open("tree108.root");
   auto t4 = f->Get<TTree>("t4");
 
   // create a pointer to an event object. This will be used
   // to read the branch values.
   auto event = new Event();
 
   // get two branches and set the branch address
   auto bntrack = t4->GetBranch("fNtrack");
   auto branch  = t4->GetBranch("event_split");
   branch->SetAddress(&event);
 
   Long64_t nevent = t4->GetEntries();
   Int_t nselected = 0;
   Int_t nb = 0;
   for (Long64_t i=0; i<nevent; i++) {
      // read branch "fNtrack"only
      bntrack->GetEntry(i);
 
      // reject events with more than 587 tracks
      if (event->GetNtrack() > 587)
         continue;
 
      // read complete accepted event in memory
      nb += t4->GetEntry(i);
      nselected++;
 
      // print the first accepted event
      if (nselected == 1)
         t4->Show();
 
      // clear tracks array
      event->Clear();
   }
 
   if (gROOT->IsBatch())
      return;
   new TBrowser();
   t4->StartViewer();
}
 
void tree108_tree()
{
   Event::Reset(); // Allow for re-run this script by cleaning static variables.
   tree108_write();
   Event::Reset(); // Allow for re-run this script by cleaning static variables.
   tree108_read();
}