TChain Merge Output Has Too Few Events

I am currently running a fairly simple C++ program to merge various Root files using TChain. I am merging around 1,000 files at a time, but each has only 2 or 3 events. The only error I get is

“Error in <TBranch::In the branch %s, no basket contains the entry %d >: CC05E391ModuleModID”

but I do get an output file with events in it. However, I am expecting the file to have 1,000-2,000 events but the file has only around 100 events. This is the code I am using:

#include <iostream>
#include <sstream>

#include "TChain.h"

using namespace std;

int main(int argc, char** argv)
        TChain join(argv[3]);
        int i;

        for(i = 9000; i < 11000; i++)

                stringstream FileName;
                FileName << argv[1]  << i << ".root";

                string FileNameS = FileName.str();


                cout << FileNameS << "\n";



        cout << "\n\n Join Done\n";

        return 0;

These files contain events generated through a Monte Carlo simulation. I doubt that there are any “repeat events” with the exact same values in all branches, but I am wondering if the merging discards repeat events so then the problem I am seeing is due to my Monte Carlo rather than with Root itself. Thank you in advance for your suggestions.

ROOT Version: 5.34/38
Platform: Not Provided
Compiler: Not Provided

v5.34 is quite ancient. Can you try with v6.22?

I can ask about upgrading the version, but I am working through the KEK computing cluster so I don’t know how feasible it will be to work with a newer version of Root. If you believe this issue is highly dependant on what version of Root I am using I can ask about upgrading my version of Root and get back to you once I know if that will be possible.

You can install ROOT in your own user area and easily use it. See for example

We would then be able to tell if the problem is with the files or with the code in ROOT.

Alternatively you can provide us with a set of failing files and we can try it out.

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