testWriteTree.cpp

// void WriteTree()
// {
//     Event *myEvent = new Event();
//     TRandom3 *r3=new TRandom3();
//     TFile* f=TFile::Open("AFile.root", "RECREATE");
//     TTree *t = new TTree("myTree","A Tree");
//     t->Branch("EventBranch", &myEvent);
//     for (int e=0;e<100000;++e) {
//         myEvent->Generate(); // hypothetical
//         // r3->Uniform(-5,5);
//         t->Fill();
//     }
//     t->Write();
// }
void testWriteTree(){
   // create a tree file tree1.root - create the file, the Tree and
   // a few branches
   TFile f("tree1.root","recreate");
   TTree t1("t1","a simple Tree with simple variables");
   Float_t px, py, pz;
   Double_t random;
   Int_t ev;
   t1.Branch("px",&px,"px/F");
   t1.Branch("py",&py,"py/F");
   t1.Branch("pz",&pz,"pz/F");
   t1.Branch("ev",&ev,"ev/I");

   // fill the tree
   for (Int_t i=0; i<10000000; i++) {
      gRandom->Rannor(px,py);
      pz = px*px + py*py;
      random = gRandom->Rndm();
      ev = i;
      t1.Fill();
   }
   // save the Tree heade; the file will be automatically closed
   // when going out of the function scope
   t1.Write();

}