[tmva] Properly manage TFile objects in tutorial

tutorials/tmva/TMVAClassification.C

@@ -172,18 +172,13 @@ int TMVAClassification( TString myMethodList = "" )
 
    // Read training and test data
    // (it is also possible to use ASCII format as input -> see TMVA Users Guide)
-   TFile *input(0);
-   TString fname = "./tmva_class_example.root";
-   if (!gSystem->AccessPathName( fname )) {
-      input = TFile::Open( fname ); // check if file in local directory exists
-   }
-   else {
-      TFile::SetCacheFileDir(".");
-      input = TFile::Open("http://root.cern/files/tmva_class_example.root", "CACHEREAD");
-   }
-   if (!input) {
-      std::cout << "ERROR: could not open data file" << std::endl;
-      exit(1);
+   // Set the cache directory for the TFile to the current directory. The input
+   // data file will be downloaded here if not present yet, then it will be read
+   // from the cache path directly.
+   TFile::SetCacheFileDir(".");
+   std::unique_ptr<TFile> input{TFile::Open("http://root.cern/files/tmva_class_example.root", "CACHEREAD")};
+   if (!input || input->IsZombie()) {
+      throw std::runtime_error("ERROR: could not open data file");
    }
    std::cout << "--- TMVAClassification       : Using input file: " << input->GetName() << std::endl;
 
@@ -193,8 +188,11 @@ int TMVAClassification( TString myMethodList = "" )
    TTree *background     = (TTree*)input->Get("TreeB");
 
    // Create a ROOT output file where TMVA will store ntuples, histograms, etc.
-   TString outfileName( "TMVAC.root" );
-   TFile* outputFile = TFile::Open( outfileName, "RECREATE" );
+   TString outfileName("TMVAC.root");
+   std::unique_ptr<TFile> outputFile{TFile::Open(outfileName, "RECREATE")};
+   if (!outputFile || outputFile->IsZombie()) {
+      throw std::runtime_error("ERROR: could not open output file");
+   }
 
    // Create the factory object. Later you can choose the methods
    // whose performance you'd like to investigate. The factory is
@@ -207,7 +205,7 @@ int TMVAClassification( TString myMethodList = "" )
    // All TMVA output can be suppressed by removing the "!" (not) in
    // front of the "Silent" argument in the option string
    auto factory = std::make_unique<TMVA::Factory>(
-      "TMVAClassification", outputFile,
+      "TMVAClassification", outputFile.get(),
       "!V:!Silent:Color:DrawProgressBar:Transformations=I;D;P;G,D:AnalysisType=Classification");
    auto dataloader_raii = std::make_unique<TMVA::DataLoader>("dataset");
    auto *dataloader = dataloader_raii.get();
@@ -538,7 +536,7 @@ int TMVAClassification( TString myMethodList = "" )
    // --------------------------------------------------------------
 
    // Save the output
-   outputFile->Close();
+   outputFile->Write();
 
    std::cout << "==> Wrote root file: " << outputFile->GetName() << std::endl;
    std::cout << "==> TMVAClassification is done!" << std::endl;