Reading of HepMC file and Plotting of x y z distribution

ROOT
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Dear Experts

I need some help to plot x y z distributions using the hepmc file on this link:

I have the following code which is suppose to plot x y z distributions but my output histograms are empty. Please help to make these distributions form this file.

#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>
#include <TCanvas.h>
#include <TH1F.h>

int main() {
  // Open the input file
  std::ifstream inputFile("bremge_1keV_eic.hepmc");

  // Create histograms to store the positions
  TH1F* hX = new TH1F("hX", "Position X Distribution", 100, -10.0, 10.0);
  TH1F* hY = new TH1F("hY", "Position Y Distribution", 100, -10.0, 10.0);
  TH1F* hZ = new TH1F("hZ", "Position Z Distribution", 100, -10.0, 10.0);

  std::string line;
  while (std::getline(inputFile, line)) {
    // Skip the header lines starting with "H"
    if (line[0] == 'H')
      continue;

    std::istringstream iss(line);
    int id;
    double px, py, pz, energy, x, y, z;

    // Read the particle ID, 4-vector components, and position
    if (iss >> id >> px >> py >> pz >> energy >> x >> y >> z) {
      // Fill the histograms with the positions
      hX->Fill(x);
      hY->Fill(y);
      hZ->Fill(z);
    } else {
      std::cerr << "Error reading line: " << line << std::endl;
    }
  }

  // Close the input file
  inputFile.close();

  // Create a canvas and draw the histograms
  TCanvas* canvas = new TCanvas("canvas", "Position Distributions", 1200, 600);
  canvas->Divide(3, 2);
  canvas->cd(1);
  hX->Draw();
  canvas->cd(2);
  hY->Draw();
  canvas->cd(3);
  hZ->Draw();

  // Save the histograms as images
  canvas->SaveAs("p1.png");

  // Clean up
  delete hX;
  delete hY;
  delete hZ;
  delete canvas;

  return 0;
}

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2

That doesn’t match the content of the file. if you want to read the lines like:

P 1 0 -11 0.0000000000000000e+00 0.0000000000000000e+00 -9.9999999869440011e+00 1.0000000000000000e+01 5.1099900095068825e-04 4

You can first change this:

   if (line[0] == 'H')
      continue;

by this:

    if (line[0] != 'P')
      continue;

And then you have to also read the first character and the last value, something like:

    char P;
    double px, py, pz, energy, x, y, z, w;

    // Read the particle ID, 4-vector components, and position
    if (iss >> P >> id >> px >> py >> pz >> energy >> x >> y >> z >> w) {

But you have to make sure the values you read are the correct ones (I don’t know what the values in that file are)