Cannot open file: TGraphErrors is Zombie

I’m completely new to Root and also to C++ coding. I’m going through the Root Primer and am trying to do the example in 2.5 for plotting measurements, which uses a file called “ExampleData.txt”, however I am getting an error when I try to execute the code. I have the file in the same folder as Root (as instructed).

Here is the code:
TGraphErrors gr(“ExampleData.txt”);

Here is the error:
Error in TGraphErrors::TGraphErrors: Cannot open file: ExampleData.txt, TGraphErrors is Zombie

As I said I am completely new to this, so thank you in advance for the help and patience.

Hi @mike.z,
That is probably because you don’t have ExampleData.txt file in the same directory where you are running ROOT prompt. You can download the data at, then try to replicate the example. Let me know should you have any more questions.

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Thank you for the response @vpadulan

I have the file in my root/bin directory. I think that is where root is running from. I source from that directory. Maybe it is not the right one?

Hi @mike.z,
So I tried to reproduce your example from top to bottom.

I will then assume that you have a folder structure similar to the following


Since this would be the common/suggested way of having a local ROOT build on your machine (see here for reference).
Then, typying source myfolder/build/bin/ will setup your current environment with ROOT.
Now, while being inside myfolder, I type root to open the ROOT prompt. At the prompt, I type the following lines:

root [0] TGraphErrors gr("ExampleData.txt");
root [1] gr.Draw();
Info in <TCanvas::MakeDefCanvas>:  created default TCanvas with name c1

And I correctly see the graph displayed. Tell me if you see anything wrong .

ROOT Version: 6.16
Platform: CentOS

Please note that the “ExampleData.txt” file must be in your “current working directory”, NOT in the “${ROOTSYS}/bin” directory.

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Thank you @Wile_E_Coyote and @vpadulan

I got it to work by following your instructions. My folder structure like this: Home/ROOT/root/bin/

I didn’t understand what “working folder” meant, and thought it referred to the /bin folder with When I put the file in my Home folder then the graph loaded properly.

Thank you again for the help and patience.

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