[ROOT] Reading array in a Tree

From: Conrad Steenberg (conrad@hep.caltech.edu)
Date: Fri Sep 06 2002 - 23:11:19 MEST 

Hi

>From reading the user's manual I'm  unsure how to read a variable array
of doubles from a TTree. E.g.

The TTree has a branch
*............................................................................*
*Br   12 :nGenjet5  : nGenjet5/I                                             *
*Entries :      638 : Total  Size=      14992 bytes  File Size  =          0 *
*Baskets :	  0 : Basket Size=	32000 bytes  Compression=   1.00     *
*............................................................................*

and another

*............................................................................*
*Br   21 :Etgenjet5 : Etgenjet5[nGenjet5]/D                                  *
*Entries :      638 : Total  Size=      36769 bytes  File Size  =          0 *
*Baskets :	  0 : Basket Size=	32000 bytes  Compression=   1.00     *
*............................................................................*


So in my Root file I do 

Int_t i, j, nGenjet5;
TArrayD *Etgenjet5=0;

//[ Set up the TTree from a file here] then

Int_t nevent = (Int_t) T->GetEntries(); 
T->SetBranchAddress("nGenjet5",&nGenjet5);  
T->SetBranchAddress("Etgenjet5",&Etgenjet5);

for (i=0;i<nevent;i++)                       // Loop over Events
{        
    T->GetEntry(i);                         
    for (j=0;j<nGenjet5;j++)
      printf("j=%d value=%f\n",j,Etgenjet5[j]);

}

This quicjly causes a segfault...

Any ideas would be appreciated :-)

Conrad

-- 
*-----------------------------------------*
| Conrad Steenberg                        |
| Caltech, Mail Code 356-48               |
| Pasadena, CA, 91125                     |
| e-mail: conrad@hep.caltech.edu          |
| Tel: (626) 395-8758                     |
*-----------------------------------------*

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