eof()は使うのに注意が必要

もしも、あなたがAWKの１行プログラムを使わずに、ROOTのマクロで同じことをしようと思えば、コードは以下のようになります。

% cat owondata.txt | awk 'NR>8 {print $1, $3}' >owondata_ch1.txt
% cat owondata.txt | awk 'NR>8 {print $1, $4}' >owondata_ch2.txt

{
  ifstream finput("owondata.txt"); // read the original file without using AWK one-liners
  Int_t nskip=8;
  std::string s;

  for(int i=0;i<nskip;i++) { // skip the first eight lines
    getline(finput, s);
  }

  const Int_t icount_max=8192;
  Int_t icount=0;
  Double_t dummy, data1[icount_max], data2[icount_max], data3[icount_max]; // save $1, $3, and $4
  while(icount < icount_max) {
    finput >> data1[icount] >> dummy >> data2[icount] >> data3[icount];
    if(finput.eof()) break;
    icount++;
  }

  TCanvas *c1 = new TCanvas("c1","Test",200,100,800,600);
  TGraph *g = new TGraph(icount, data1, data2); // ch1 data
  g->SetMarkerStyle( 20 ); 
  g->SetMarkerSize( 0.5 );
  g->Draw("AP");
  TF1 *f1 = new TF1("f1", "[0]*sin([1]*x+[2])-[3]");
  f1->SetParameter(0, 2000.0);
  f1->SetParameter(1, 0.022);
  f1->SetParameter(2, 0.0);
  f1->SetParameter(3, 0.0);
  f1->SetLineColor(kRed);
  g->Fit(f1);

  TGraph *h = new TGraph(icount, data1, data3); // ch2 data
  h->SetMarkerStyle( 24 ); 
  h->SetMarkerSize( 0.5 );
  h->Draw("P");
  TF1 *f2 = new TF1("f2", "[0]*sin([1]*x+[2])-[3]");
  f2->SetParameter(0, 2000.0);
  f2->SetParameter(1, 0.022);
  f2->SetParameter(2, 0.0);
  f2->SetParameter(3, 0.0);
  f2->SetLineColor(kYellow);
  h->Fit(f2);

  double amp, phase;
  amp   = f2->GetParameter(0) / f1->GetParameter(0);
  phase = f2->GetParameter(2) - f1->GetParameter(2);
  std::cout << amp << ", " << phase << std::endl;

  TComplex v1, v2, v3, Z, z50;
  v1  = TComplex(1.0, 0.0);
  v2  = TComplex( amp*TMath::Cos(phase), amp*TMath::Sin(phase) );
  v3  = 2.0*v1 - v2;
  z   = v2/v3;
  z50 = 50.0*z;
  std::cout << v1 << ", " << v2 << ", " << v3 << ", " << z << ", " << z50 << std::endl;

  TComplex rho;
  double vswr;
  rho  = (z-1.0)/(z+1.0);
  vswr = (1.0+TComplex::Abs(rho)) / (1.0-TComplex::Abs(rho));
  std::cout << rho << ", " << vswr << std::endl;
}

以下のようなコードは、icountをwhile loopの外で１だけ減らさない限り、うまく動作しないことに留意して下さい。

while(! finput.eof() ) }
  finput >> ...
  icount++;
}