copytree.C

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/// \file
/// \ingroup tutorial_tree
/// \notebook -nodraw
/// Copy a subset of a Tree to a new Tree
///
/// The input file has been generated by the program in `$ROOTSYS/test/Event`
/// with `Event 1000 1 1 1`.
///
/// \macro_code
///
/// \author Rene Brun

R__LOAD_LIBRARY($ROOTSYS/test/libEvent.so)

void copytree() {
   //Get old file, old tree and set top branch address
   TFile *oldfile;
   TString dir = "$ROOTSYS/test/Event.root";
   gSystem->ExpandPathName(dir);
   if (!gSystem->AccessPathName(dir))
       {oldfile = new TFile("$ROOTSYS/test/Event.root");}
   else {oldfile = new TFile("./Event.root");}
   TTree *oldtree = (TTree*)oldfile->Get("T");
   Event *event   = new Event();
   oldtree->SetBranchAddress("event",&event);
   oldtree->SetBranchStatus("*",0);
   oldtree->SetBranchStatus("event",1);
   oldtree->SetBranchStatus("fNtrack",1);
   oldtree->SetBranchStatus("fNseg",1);
   oldtree->SetBranchStatus("fH",1);

   //Create a new file + a clone of old tree in new file
   TFile *newfile = new TFile("small.root","recreate");
   TTree *newtree = oldtree->CloneTree();

   newtree->Print();
   newfile->Write();
   delete oldfile;
   delete newfile;
}