[ROOT] Problem storing/reading TString in TTree

From: cstrato@EUnet.at
Date: Sun Jan 21 2001 - 18:42:05 MET 

Dear Rooters

I would like to store names as TString in a treebranch, but have
problems in reading them back.

I have a class "TestClass" which I use in TBranch. The following
code in macro1 seems to work but in macro2 I can only read back
the number vFloat but not the name vName:

---------macro1.C---------------
{
   TFile *vFile = new TFile("test.root","RECREATE");
   TTree *vTree = new TTree("vTree","data from file name.txt");
   TestClass *vTest = new TestClass();
   TBranch *vBranch =
vTree->Branch("vBranch","TestClass",&vTest,256000,1);

   ifstream vInput.open("name.txt", ios::in);

// I tested the following three definitions
// which one should I use?
   char* vName = new char[8];
   char vName[8];
   TString  vName;

   for (Int_t i=0;i<1000;i++) {
      vInput >> vFloat >> vName;
      if (!vInput.good()) break;

      vTest->FSetFloat(vFloat);
      vTest->FSetName(vName);

      vTree->Fill();
      vTest->Clear();
   }

   vInput.close();
   vTree->Write();

   delete vTest;
   delete [] vName;
}

---------macro2.C---------------
{
   TFile *vFile = new TFile("test.root","READ");
   TTree *vTree = (TTree*)vFile->Get("vTree");
   TestClass *vTest = new TestClass();
   vTree->SetBranchAddress("vBranch",&vTest);

// none of the following three definitions seems to work
   char* vName = new char[8];
   char vName[8];
   TString  vName;

   for (Int_t i=0;i<1000;i++) {
      vTree->GetEntry(i);

      vFloat = vTest->FGetFloat();
      vName = vTest->FGetName();

// this prints vFloat correctly, but random chars for vName
      printf("vFloat=%.3lf,vName=%s\n", vFloat, vName);
// this prints vFloat correctly, but nothing for vName
      cout << "vFloat= " << vFloat  << " vName= " << vName << endl;
   }

   delete vTest;
   delete [] vName;
}

---------TestClass--------------
class TestClass: public TObject {

   private:
      TString       fName;
      Float_t       fFloat;

   public :

      TestClass();
      ~TestClass();

      void FSetFloat(Float_t vFloat) {fFloat = vFloat;}
// first test to store TString
      void FSetName(const char *vName) {fName = vName;}
// second test to store TString: should I use this function?
      void FSetName(const char *vName) {fName = TString(vName,8);}

      Float_t FGetFloat() const {return fFloat;}
      const char* FGetName() const {return fName;}

      ClassDef(TestClass,1) //TestClass
};

//--------------------
#include "TestClass.h"

ClassImp(TestClass);

TestClass::TestClass(): TObject()
{
}

TestClass::~TestClass()
{
}//Destructor
//--------------------

Could you please tell me what I am doing wrong? I tested differnt
ways to read back TString, but none of them seem to work.

Thank you in advance for your help.

Best regards
Christian Stratowa
Vienna, Austria

My system: PowerBook running LinuxPPC 2000
           root 3.00/01  22 December 2000

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