Pointer returned from macro function is losing content

TMVA
1

In ROOT 6.08/06, I am running a fairly simple macro. It takes two arguments to open a file and find a TTree in that file. Once I have the TTree*, I can pass it around to do other things (plotting, etc.).

The problem I have is that the pointer which gets returned by my function is corrupt. Here’s the function code, including debugging output:

TTree* getTree(const TString& fname, const TString& type) {
  TFile file(fname);
  if (!file.IsOpen()) {
    std::cerr << "ERROR opening " << fname << std::endl;
    return 0;
  }

  TString treestr = "G4SimDir/g4dmc"+type;
  const char* treename = treestr.Data();
  std::cout << "Looking for " << treename << " in " << file.GetName()
	    << std::endl;

  TTree* tree = 0;
  file.GetObject(treename, tree);

  std::cout << "Got object @ " << tree << " of type " << tree->ClassName()
	    << " named " << tree->GetName() << std::endl;
  
  return tree;
}

Here’s the top-level macro where it gets called, along with a debugging statement:

int G4DMCtrace(const TString& fname, const TString& type,
	       Long64_t evt, Int_t chan) {
  TTree* tree = getTree(fname, type);
  if (!tree) return 2;

  std::cout << "In main, tree @ " << tree << " of type " << tree->ClassName()
	    << " named " << tree->GetName() << std::endl;

And finally, here’s what gets printed out when I run it. The file itself is valid (I can open it in TBrowser and the content I expect is all there):

{michaels-mbp:260} root -l -q -b G4DMCtrace.C'("TES_10180328_0000.root","TES",0,0)' | & more

Processing G4DMCtrace.C("TES_10180328_0000.root","TES",0,0)...
Looking for G4SimDir/g4dmcTES in TES_10180328_0000.root
Got object @ 0x7f88cfe4ba20 of type TTree named g4dmcTES
In main, tree @ 0x7f88cfe4ba20 of type TObject named TObject

 *** Break *** segmentation violation
[<unknown binary>]
[<unknown binary>]

Notice that the pointer address returned is the same as it was inside the getTree() function, but the information content (ClassName, tree name, etc.) are hosed.

2

Never mind. The performance is as expected, because I wrote my function with a TFile file declaration, instead of TFile *file = new TFile. When file goes out of scope, the extracted pointers are no longer guaranteed to be valid.