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 $ROOTSYS/test/eventb.C It shows:
char fType[20];
Int_t fNtrack;
Int_t fNseg;
Int_t fNvertex;
UInt_t fFlag;
Float_t fTemperature;
EventHeader fEvtHdr;
TClonesArray *fTracks; //->
TH1F *fH; //->
Int_t fMeasures[10];
Float_t fMatrix[4][4];
Float_t *fClosestDistance; //[fNvertex]
This example can be run in many different ways:
.x tree4.C
.L tree4.C
tree4()
.L ../test/libEvent.so
.x tree4.C++
One can also run the write and read parts in two separate sessions. For example following one of the sessions above, one can start the session:
.L tree4.C
tree4r();
Author: Rene Brun
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Wednesday, April 17, 2024 at 11:24 AM.
Definition of a helper function:
%%cpp -d
R__LOAD_LIBRARY($ROOTSYS/test/libEvent.so)
#include "TFile.h"
#include "TTree.h"
#include "TBrowser.h"
#include "TH2.h"
#include "TRandom.h"
#include "TClassTable.h"
#include "TSystem.h"
#include "TROOT.h"
TString dir = "$ROOTSYS/test/Event.h";
gSystem->ExpandPathName(dir);
TString includeCommand = TString::Format("#include \"%s\"" , dir.Data());
gROOT->ProcessLine(includeCommand);
void tree4w()
{
//create a Tree file tree4.root
TFile f("tree4.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();
}
input_line_44:8:1: error: function definition is not allowed here { ^
Definition of a helper function:
%%cpp -d
void tree4r()
{
// read the tree generated with tree4w
//note that we use "new" to create the TFile and TTree objects !
//because we want to keep these objects alive when we leave this function.
TFile *f = new TFile("tree4.root");
TTree *t4 = (TTree*)f->Get("t4");
// create a pointer to an event object. This will be used
// to read the branch values.
Event *event = new Event();
// get two branches and set the branch address
TBranch *bntrack = t4->GetBranch("fNtrack");
TBranch *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();
}
Event::Reset(); // Allow for re-run this script by cleaning static variables.
tree4w();
Event::Reset(); // Allow for re-run this script by cleaning static variables.
tree4r();
input_line_55:2:3: error: use of undeclared identifier 'tree4w' (tree4w()) ^ Error in <HandleInterpreterException>: Error evaluating expression (tree4w()) Execution of your code was aborted.