[ROOT] problem with reading and filling ntuples

From: Meulenhoff, P.J. (P.J.Meulenhoff@kpn.com)
Date: Tue Oct 17 2000 - 12:53:25 MEST 

Hi Rooters,

Running the following macro (plot.C) gives some unexpected results. The
macro has two functions: fill() and analysis(). The fill routine fills the
ntuple: ntuple with the variable x,y and z. x,y, and z are always equal to
5. The analysis routine reads all entries in the ntuple created in the fill
routine. A new ntuple: analysis is created.  The main routine (plot()) calls
fill() and analysis() several times.

When the root is started from the command line (of a linux redhat 6.2 box):

root -l -q plot.C

the following output is produced


-- start output
  *******************************************
  *                                         *
  *        W E L C O M E  to  R O O T       *
  *                                         *
  *   Version   2.25/03   11 October 2000   *
  *                                         *
  *  You are welcome to visit our Web site  *
  *          http://root.cern.ch            *
  *                                         *
  *******************************************

Compiled with thread support.

CINT/ROOT C/C++ Interpreter version 5.14.50, Sep 2 2000
Type ? for help. Commands must be C++ statements.
Enclose multiple statements between { }.

Processing plot.C...
this is fill
this is analysis
i = 0 x =    5.000 y =    5.000 z =    5.000
this is fill
this is analysis
i = 0 x =    5.000 y =    5.000 z =    5.000
i = 1 x =    5.240 y =    5.240 z =    0.000
-- end of output

The last line is VERY strange. This values of x,y and z should all be equal
to 5.

This is the source code of the macro:

//-----start of plot.C
void fill() {
  printf("this is fill\n");

  TNtuple *ntuple = (TNtuple *)gDirectory->Get("ntuple");
  if ( ntuple == NULL ) {
    ntuple = new TNtuple("ntuple","ntuple","x:y:z");
  }

  Float_t x = 5.0;
  Float_t y = 5.0;
  Float_t z = 5.0;
  
  ntuple->Fill(x,y,z); 
}

void analysis() {
  printf("this is analysis\n");
  
  TNtuple *analysis = (TNtuple *)gDirectory->Get("analysis");
  if ( analysis == NULL ) {
    analysis = new TNtuple("analysis","analysis","x:y:z");
  }

  TNtuple *ntuple = (TNtuple *)gDirectory->Get("ntuple");
  
  Float_t x,x1;
  Float_t y,y1;
  Float_t z,z1;
    
  if ( ntuple != NULL ) {

    ntuple->SetBranchAddress("x",&x);
    ntuple->SetBranchAddress("y",&y);
    ntuple->SetBranchAddress("z",&z);
       
    int nentries = ntuple->GetEntries();
    
    for(int i=0;(i<nentries);i++) {
      ntuple->GetEntry(i);
      x1 = x + 1.0;
      y1 = y + 1.0;
      z1 = z + 1.0;
      analysis->Fill(x1,y1,z1);

      printf("i = %d x = %8.3f y = %8.3f z = %8.3f\n",i,x,y,z);
    }
  }
}

void plot() {
  fill();
  analysis();
  fill();
  analysis();
}
// end of plot.C


Pieter Meulenhoff
p.j.meulenhoff@kpn.com
KPN Research
Groningen, The Netherlands

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