Error adding branch

ROOT
1

If I want to store an array (c array) in a TTree, I need to store the dimension in an other branch. This is ok, and I can use variable length array, the problem is when the array length is stored in a friend TTree. For example:

#include "TROOT.h"
#include "TTree.h"
#include "TFile.h"

int main(int argc,char **argv)
{

    // Fill a branch of a tree with "random" integers

    TFile tree_file("tree_file.root","recreate");
    TTree *tree = new TTree("tree","main tree");
    int n = 10;
    const Int_t n_entries = 100;
    tree->Branch("n",&n,"n/I");

    for (int i=0;i<n_entries;++i) {
	n = ( 7 * n + 6 ) % 101;
	tree->Fill();
    }
    
    // and write on a file

    tree_file.cd();
    tree_file.Write();

    // Create a second tree
    
    TFile second_file("friend_file.root","recreate");
    TTree *second_tree = new TTree("second_tree","second tree");
    
    // the fist is now a friend of the second
    second_tree->AddFriend(tree);

    Float_t array[100];
    Float_t array2[100];

    Int_t j;    

    second_tree->Branch("j",&j,"j/I");    
    // this is ok:
    second_tree->Branch("Ns",array,"Ns[j]/F");
    //this is not ok. Why? n is a branch of a friend!
    second_tree->Branch("N2s",array2,"N2s[n]/F");   
    // output: Error in <TBranch::TBranch>: Illegal leaf: N2s/N2s[n]/F

    return 0;
}

I don’t know if is it a bug, or maybe I’m asking to much from ROOT.

2

Hi,

You must have the ‘size’ of an array stored in the same TTree (otherwise the TTree without the ‘size’ branch will not be readable without the ‘main’ tree).
I recommend you simply duplicate the information in both the main and friend tree.

Cheers,
Philippe