#include <TROOT.h>
#include <TH1.h>
#include <TCanvas.h>

#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
#include <cstdio>

#define NOFCHANNELS 5

int glow(const char *fname = "trial_3.txt")
{
  int npoints = 0;
  // http://www.cplusplus.com/reference/string/
  std::string line;
  
  // http://www.cplusplus.com/reference/iostream/ifstream/
  std::ifstream ifs(fname);
  
  while(1) {
    // http://www.cplusplus.com/reference/string/getline/
    getline(ifs, line);
    if ( ! ifs.good() ) break;
    npoints++;
  } // while(1)
  
#if 0 /* 0 or 1 */
  std::cout << "npoints = " << npoints << std::endl;
#endif /* 0 or 1 */
  
  if (npoints < 1) return npoints;
  
  ifs.clear();
  ifs.seekg(0);
  
  TH1F *histo[(NOFCHANNELS)];	
  char name[50];
  
  for(int i = 0; i < (NOFCHANNELS); i++) {
    snprintf(name, sizeof(name), "channel_%d", i + 1);
    
    gROOT->GetObject(name, histo[i]);
    if (histo[i]) delete histo[i];
    
    histo[i] = new TH1F(name, name, npoints, 0, npoints);
  } // for(int i = 0; i < (NOFCHANNELS); i++)
  
  for(int i = 0; i < npoints; i++) {
    // http://www.cplusplus.com/reference/string/getline/
    getline(ifs, line);
    if ( ! ifs.good() ) {
      std::cout << "ERROR reading line : " << (i + 1) << std::endl;
      break;
    } // if ( ! ifs.good() )
    
    // http://www.cplusplus.com/reference/iostream/istringstream/
    istringstream s(line);
    
    for(int j = 0; j < (NOFCHANNELS); j++) {
#if 1 /* 0 or 1 */
      s >> (histo[j]->GetArray())[(i + 1)]; // "number of entries" not changed
      if ( ! s.good() ) {
	std::cout << "ERROR in line : " << (i + 1)
		  << " : in column : " << j << " or " << (j + 1)
		  << std::endl;
	break;
      } // if ( ! s.good() )
      histo[j]->SetEntries(histo[j]->GetEntries() + 1.0);
#else /* 0 or 1 */
      double tmp = 0.0;
      s >> tmp;
      if ( ! s.good() ) {
	std::cout << "ERROR in line : " << (i + 1)
		  << " : in column : " << j << " or " << (j + 1)
		  << std::endl;
	break;
      } // if ( ! s.good() )
      histo[j]->SetBinContent(i + 1, tmp); // "number of entries" incremented
#endif /* 0 or 1 */
    } // for(int j = 0; j < (NOFCHANNELS); j++)
  } // for(int i = 0; i < npoints; i++)
  
  TCanvas *c = (TCanvas *)gROOT->GetListOfCanvases()->FindObject("c");
  if (c) delete c;
  c = new TCanvas("c", "c", 500, ((NOFCHANNELS) * 190));
  
  c->Divide(1, (NOFCHANNELS));
  // c->Modified();
  // c->Update();
  
  for(int i = 0; i < (NOFCHANNELS); i++) {
    c->cd(i + 1);
    histo[i]->Draw("C");
  } // for(int i = 0; i < (NOFCHANNELS); i++)
  
  c->cd(0);
  // c->Modified();
  c->Update();
  
  return npoints;
} // int glow(const char *fname = "trial_3.txt")