Problem reading TGraphErrors from TFile

ROOT
1

Hi all,

I’ve a problem I can’t figure out. I’m am getting several TGraphErrors from different TFiles.

When I use:

 TFile *f1 = TFile::Open("Plots/MyRootFile1.root", "READ");
f1->ls();  cout << endl;

 TGraphErrors * gAND1 = (TGraphErrors*)f1->Get("Ar:CO_{2} 70:30 - Thr12-Lat14");

It works. I read three different rootfiles and get three different TGraphErrros in the same way, and I get no problem.

Later in the code I do exactly the same with another rootfile and another Graph:

 TFile *f4 = TFile::Open("Plots/MyRootFile2.root", "READ"); 
f4->ls();  cout << endl;
 TGraphErrors * gX = (TGraphErrors*)f4->Get("Ar:CO_{2}:CF_{4} 45:15:40 - Thr20-Lat14"); 
 gX->SetMarkerColor(kBlue);

The TFile is read because command “f4->ls()” correctly lists the content of the file.
But I get the error:

   Error: illegal pointer to class object gX 0x0 1675  print.C:224:
   *** Interpreter error recovered ***

I really don’t understand what’s the reason, I don’t see any difference from the working code and the not workin one. Maybe it’s stupid, but could it be the length of the key?

Thanks for any hellp,
Best

2

The TGraphErrors name looks a bit complex:

“Ar:CO_{2}:CF_{4} 45:15:40 - Thr20-Lat14”

Are you sure you have not made any mistake typing it ?

3

Hi,

this was also my first guess.

So I copied and pasted the name of the TGraphErrors many times copying it from the output of f4->ls() command.

Precisely, it shows:
[b] KEY: TGraphErrors Ar:CO_{2}:CF_{4} 45:15:40

  • Thr20-Lat15;1 Ar:CO_{2}:CF_{4} 45:15:40
  • Thr20-Lat15[/b]

I noticed that the key is printed on two lines, separated in between “45:15:40” and " - Thr".
I checked the TString that gives such name: there’s no newline there.

I have tried:

TGraphErrors * gX = (TGraphErrors*)f4->Get("Ar:CO_{2}:CF_{4} 45:15:40\n - Thr20-Lat14");
TGraphErrors * gX = (TGraphErrors*)f4->Get("Ar:CO_{2}:CF_{4} 45:15:40
 - Thr20-Lat14");
TGraphErrors * gX = (TGraphErrors*)f4->Get("Ar:CO_{2}:CF_{4} 45:15:40 - Thr20-Lat14;1");

But no way…

4

May be this can help:

root.cern.ch/how/how-draw-objec … s-its-name

5

If I correctly understood this code, I have to set
obj_name = “ThisIsMyGraphsName” ;
In this way I get the same error, because I have to write manually the name of the TGraphErrors.

Anyway I have mixed it with another idea.
This is a bit tricky, but I used the following code:

// get the list of keys
   TList *list = (TList *)f4->GetListOfKeys();
   if (!list) {
      std::cout << "Cannot get the list of TKeys! Aborting..." << std::endl;
      return;
   }
   
   TObject *obj;
   TListIter *it = new TListIter(list,kIterForward);
   TString GrName;
   while ((obj = it->Next()))
     {
     TString title = obj->GetTitle();
     if (  title.BeginsWith("Ar:CO_{2}:CF_{4}") && title.EndsWith("Thr20-Lat14"))
     GrName = obj->GetTitle();
     }
     
  cout << GrName << endl;

The Title printed on screen is:
Ar:CO_{2}:CF_{4} 45:15:40

  • Thr20-Lat14

If now I get tha TGraphErrors like this:

TGraphErrors * gX = (TGraphErrors*)f4->Get(GrName);

it works. A bit tricky but… at least it works.

Thanks!

6

yes your graph names are more like graph titles … you should make a difference … the name is the handle you use to access them so, if there is some control characters in it (I suspect “:” might be one) then you cannot access it by name.