ROOT file. Access to histograms

[Cellamare]

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Hi guys,

I have a problem with a macro I wrote to access histograms stored in a ROOT file.
The file contains histograms named “Fiber_0”, “Fiber_1” and “Fiber_2”.

Now, with the macro I wrote (see the screenshot) I’m able to retrieve only one of them using the code lines I commented. But, when I try to loop over them I have problems. Moreover, I don’t know how to index histogram names.

Could anyone help me?

Cheers.

[Wile_E_Coyote]

TH1D *hist; file->GetObject(TString::Format("Fiber_%d", i), hist);
if (!hist) continue; // just a precaution

[Cellamare]

@Wile_E_Coyote

TH1D *hist; file->GetObject(TString::Format("Fiber_%d", i), hist);

Hi,
I wrote this
for(i=0;i<NofLayers;i++){
TH1D *hist;
file->GetObject(TString::Format(“Fiber_%d”, i), hist);
hist->Draw();
//hist->SetDirectory(gROOT);
}//for end

but I got error: cannot initialize an array element of type ‘void ’ with an rvalue of type 'TString ()(const char *, …)’

[Wile_E_Coyote]

{
  TFile *file = TFile::Open("/path/to/file.root");
  if (!file || file->IsZombie()) { delete file; file = 0; } // just a precaution
  if (file) file->ls();
  int NofLayers = 3;
  for(int i = 0; i < NofLayers; i++) {
    TH1D *hist = 0;
    if (file) file->GetObject(TString::Format("Fiber_%d", i), hist);
    if (!hist) continue; // just a precaution
    hist->SetDirectory(gROOT);
    new TCanvas(); hist->Draw(); // each histogram in its own canvas
  }
  delete file; file = 0;
}

[Cellamare]

@Wile_E_Coyote

for(int i = 0; i < NofLayers; i++) {
  TH1D *hist; file->GetObject(TString::Format("Fiber_%d", i), hist);
  if (!hist) continue; // just a precaution
  hist->SetDirectory(gROOT);
  new TCanvas(); hist->Draw(); // each histogram in its own canvas
}
delete file; // close ROOT file

I get segmentation violation

[Wile_E_Coyote]

Attach your complete macro.

[Cellamare]

{
//Open the ROOT file
TFile *file = TFile::Open(“path_to_file”);

//See what the ROOT file contains
file->ls();

//total number of fibers/histograms
int NofFibers = 3;

//Retrieve histograms from the tree

/*
TH1D* h = (TH1D*)file->Get(“Fiber_2”);
h->Draw();
h->SetDirectory(gROOT);
*/

for(int i=0; i<NofLayers ;i++){
TH1D *hist;
file->GetObject(TString::Format(“Fiber_%d”, i), hist);
//TH1D hist = (TH1D)file->GetObject(TString::Format(“Fiber_%d”,i),hist));
hist->Draw();
hist->SetDirectory(gROOT);
}//for end

for(int i = 0; i < NofLayers; i++) {
TH1D *hist;
file->GetObject(TString::Format(“Fiber_%d”, i), hist);
if (!hist) continue; // just a precaution
hist->SetDirectory(gROOT);
new TCanvas();
hist->Draw(); // each histogram in its own canvas
}
delete file; // close ROOT file

//close ROOT file
//file->Close();

} //macro end

[Wile_E_Coyote]

Try the complete macro from my previous post.

[Cellamare]

Yes!!

Now it works!

Thanks!