Hi Tommaso,
Variables in a TNtuple are of type Float_t not Double_t.
You have two other problems in your script
- never use gROOT->Reset() in a named macro
- the loop index starts at 0, not 1
You have 3 ways (at least) to check the content of your ntuple.
- using teh browser, double click on your variable "p"
- use nf->Show(ki) to dump the values of entry ki
- use nf->Scan();
Rene Brun
Tommaso Chiarusi wrote:
>
> Hello rooters,
>
> According to the userguide, I wrote the following:
> Note:
> 1. "vario.root" is the root file in which I have stored my ntuple.
> 2. "front" is the name of my ntuple (in "vario.root" there are many
> other ntuples!).
> 3. "p" is the variable that I want to plot. ("p" is either the name of
> the TLeaf inside the ntuple "front" and of the variable the histogram I
> fill with)
>
> The problem I get is that I actually do NOT Get the Entry value, but
> something like 5.30784e-315!!!!!
>
> Thank you very much!
>
> void plot()
> {
> gROOT->Reset();
>
> TFile *f = new TFile("vario.root");
> TNtuple *nf = (TNtuple*)f->Get("front");
>
>
> Int_t entries = (Int_t)nf->GetEntries();
> cout<<"Number of Entries: "<<entries<< endl;
>
>
> Double_t p=0;
> nf->SetBranchAddress("p",&p);
>
> TH1F *htp = new TH1F("htp","p",100,0,10);
>
> for (Int_t ki=1;ki<entries;ki++)
> {
> nf->GetEntry(ki);
> htp->Fill(p);
> }
>
> TCanvas *c1 = new TCanvas("c1", "c1",515,210,540,376);
> c1->Draw();
> htp->Draw();
>
> //
> }
>
> Tommaso
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