Superimpose Historgrams

ROOT
1

I know this is a bit remedial subject but help would be greatly appreciated. So I have number of historgrams that I would like to superimpose on each other. I thought such would be sufficient:


TFile *f1 = TFile::Open("Histogram1.root");
TFile *f2 = TFile::Open("Histogram2.root");
TH1 *h1 = (TH1*)f1->Get("histo1");
TH1 *h2 = (TH1*)f2->Get("histo2");
h1->Draw();
h2.Draw("same");

In general I have 2 histograms, the 1st i want to make the base and I would like to superimpose the other on it. Is there some thing that I am doing wrong here? Any Suggestions? Thanks

Cheers,
Edwin Baldelomar

2

Hi,

How does your example ‘fail’?

Philippe.

3

Hi Philippe,

Thank you for your quick response. THe error is as follows:

root [16] h1->Draw();
Error: illegal pointer to class object h1 0x0 1211  (tmpfile):1:
*** Interpreter error recovered ***
root [17] h2.Draw("same");
Error: illegal pointer to class object h2 0x0 1211  (tmpfile):1:
*** Interpreter error recovered ***

I’m not sure what this means. Thank You for your help.

Cheers,
Edwin Baldelomar

4

Hi,

Those error indicates that you have not been successful in retrieving the histogram from the file (and/or you close the files). Try:

TFile *f1 = TFile::Open("Histogram1.root"); if (f1==0) { cout << "Humm no file named Histogram1.root in the current directory.\n"; } else { TH1 *h1; f1->GetObject("histo1",h1); if (h1==0) { cout << "humm no histo named histo1 in the file!\nlet's see what's in it:\n"; f1->ls(); } }
Cheers,
Philippe.