Writing text file

[nice]

I have the root file,now i need to generate the text file from it i.e. the graph contents which is the x and the y values
which would be seen as two columns in that text file like saying getting back the ASCII values of the data in the .txt format from the .root file.
I am doing the following :-

void use()
{
TFile *f=new TFile("10th nov 04.root"); // opens the root file
TH1F * tr=(TH1F *)f->Get("htemp");

float a,b;

ofstream myfile;
myfile.open ("new example.txt");
myfile << "a  b\n";

for (int idx=0; idx <tr->GetNbinsX();idx++) {
   a = tr->GetBinCenter(idx);
   b = tr->GetBinContent(idx);
   cout << a << "  " << b << endl; //print to the screen
   myfile << a << "  " << b << "\n"; //write to file
}

myfile.close();

}

the .txt file is getting generated but its blank,it doesn’t have any data in it from the graph.
Now what’s the error in this ? yours help is welcome !
I am attaching the .root fie which you can see. 10th nov 04 N.root (19.9 KB)

[nice]

sorry for the misprint there,its actually 10th nov 04 N.root in the above program,so make the changes accordingly
although i did it right while performing the above.

[nice]

now i am running it again,i am getting the following the error :-

Error: illegal pointer to class object tr 0x0 1436 F:\root\2017project\use.c(31)
Error: Binary operator oprand missing F:\root\2017project\use.c(31)

[sbinet]

hi,

I only see a TCanvas in that file:

$> root-ls -t ./nice-26068.root 
=== [./nice-26068.root] ===
version: 53436
2017/08/31 08:53:51 rootio: adding dummy factory for "TCanvas"
TCanvas c1      canvas  (cycle=1)

[Wile_E_Coyote]

{
  TFile *f = TFile::Open("10th nov 04 N.root");
  f->ls();
  TCanvas *c; f->GetObject("c1", c);
  c->ls();
  TGraph *g = ((TGraph *)(c->FindObject("Graph")));
  // g->Print();
  for (int i = 0; i < g->GetN(); i++)
    std::cout << i << " " << g->GetX()[i] << " " << g->GetY()[i] << std::endl;
}

[nice]

Thanks dear,now its working.