The histogram cannot read rootfile to fillup. It is just empty

Newbie
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1

ROOT Version: latest
Platform: M1
Compiler: VSCode

I am having a hard time making a histogram from the root file, every time it displays an empty canvas. But using direct commands like DataTree->Draw(“SampleStream.ch0_data”) display the histogram. I want to make a histogram so that I can fit the data and can include all the necessary information in a single canvas.The root file has one tree one branch, and other leaves. I am trying to plot a histogram from a leaf. Any help and suggestions for this will be greatly appreciated. Thank you.
I have started with this coding,

#include <iostream>
#include <TH2.h>
#include "TFile.h"
#include "TTree.h"
#include "TBranch.h"
#include "TH1F.h"
#include <TStyle.h>
#include <TCanvas.h>
#include <fstream>
#include "TSystem.h"
#include "TPaveLabel.h"

void extractRoot() {
    // Read the root file
    TString fileName = "Int_Run_020-020.root";
    TFile* file = TFile::Open(fileName);

    // Check if the file is open
    if (!file) {
        std::cerr << "Error opening file: " << fileName << std::endl;
        return;
    }

    // Get the tree from the file
    TTree* tree = dynamic_cast<TTree*>(file->Get("DataTree"));
    
    TBranch* sampleStreamBranch = tree->GetBranch("SampleStream.ch0_sum");

    // Check if the branch exists
    if (!sampleStreamBranch) {
        std::cerr << "Error retrieving SampleStream.ch0_sum branch" << std::endl;
        file->Close();
        return;
    }

    // Get the first entry of the ch0_sum branch
    sampleStreamBranch->GetEntry(0);

    // Defining variables
    std::vector<double> tStmp;
    std::vector<double> ch0_data;
    std::vector<double> ch1_data;
    double ch0_sum;

    // Set branch addresses.
    tree->SetBranchAddress("tStmp", &tStmp);
    tree->SetBranchAddress("ch0_data", &ch0_data);
    tree->SetBranchAddress("ch1_data", &ch1_data);
    tree->SetBranchAddress("ch0_sum", &ch0_sum);
    gStyle->SetOptStat(1111); //sets the option for the statistics box in ROOT to display all items.


    // Create a histogram
    TH1F* histogram = new TH1F("hist", "ch0_sum Histogram", 10, 0, 2);

    // Fill the histogram
    for (Long64_t i = 0; i < tree->GetEntries(); ++i) {
        tree->GetEntry(i);
        histogram->Fill(ch0_sum);
    }

    // Plot the histogram
    TCanvas* canvas = new TCanvas("canvas", "Histogram Canvas");
    histogram->Draw();

    file->Close();
}

int main() {
    extractRoot();
    return 0;
}
2

See the “analysis skeleton” generated by:

root -b -l -q Int_Run_020-020.root -e 'DataTree->MakeClass();'

BTW.

gROOT->cd(); // newly created histograms should go here
TH1F *histogram = new TH1F(...);
3

Thank you, that makes a lot of sense.