Reading variable sized array from TTree

Newbie
1

ROOT Version: master
Platform: Linux 5.4 (Manjaro)
Compiler: GCC 9.3

I can create a ROOT file with a variable sized array of type Long64_t like this -

#include "TFile.h"
#include "TTree.h"
#include "TBranch.h"

void jagged3() {
    TFile *f = new TFile("jagged.root", "RECREATE");
    f->SetCompressionLevel(0);
    TTree *t = new TTree("t", "");
    Int_t n = 1;
    t->Branch("n", &n, "n/I");
    Long64_t branch[100];
    Long64_t count = 0;
    t->Branch("branch", branch, "branch[n]/L");
    for (int i=0; i<3; i++) {
        for (int j=0; j<n; j++) {
            branch[j] = count;
            count = count + 1;
        }
        t->Fill();
        n = n + 1;
    }
    t->Write();
    f->Close();
}

How do I read this out in ROOT?
The code to read it out would probably look something like this (I assume) -

#include "TFile.h"
#include "TTree.h"
#include "TBranch.h"
#include <stdio.h>

void readint() {
    TFile *f = new TFile("jagged.root");
    Long64_t x;
    auto tree = f->Get<TTree>("t");
    auto branch = tree->GetBranch("branch");
    branch->SetAddress(&x);
    for (int i=0; i<tree->GetEntries(); i++) {
        tree->GetEvent(i);
        for (int j=0; j<#number of entries in current event#; j++) {
            printf("%lld\n", x);
        }
    }
}

But for this how do I get the number of entries in a particular event?

My main intention is to read this out in Python(into lists or numpy arrays), so once I have a working C/C++ code where I can read it successfully, I would read it out in Python using ROOT.gInterpreter.Declare. I know this can probably be achieved in an easier way like -

    f = ROOT.TFile.Open("jagged.root")
    tree = f.Get("t")
    for _, event in enumerate(tree):
        print([x for x in event.branch])

but I am trying to avoid doing that.

2