Returning a histogram pointer

[jason777777777]

Hello,
I am defining a C++ function in which I hope it will return a pointer of a 1-D histogram. I set the type of the function return as “TH1F* function_name(…){…}” and the final command is just the usual “return h” (h is a pointer). However, after running in root, it gives me an error message saying: “Return type mismatch. TH1F not a public base,” can you help to explain what this line means? and how can i correct it?
PS: i just start using root and coding in C++, so any instruction is appreciated!
Thanks a lot!
Best,
Jason

[Danilo]

Hi Jason,

what is the body of the function? Can you share it in a post?

D

[jason777777777]

Yes, Here is the basic contents:
TH1F* photon_received(char* inputfile){
TH1* h = new TH1F(“h”, “photon_received/event”, 20, 0.0, 20.0);
{a for loop filling the pointer h…}
h->Draw();
return h;
}

When I call the function, I just use commands that:
TH1* histo = photon_received(“file_name”);

And then I receive the above error message. Am I doing anything wrong?
Thanks!

[Wile_E_Coyote]

You should have TH1F *h = ... and then TH1F *histo = ...

[behrenhoff]

Just return a TH1* from the function. You should only use the concrete type TH1F or TH1D in the “new TH1F” or “new TH1D” line. Otherwise use TH1* everywhere.

TH1* photon_received(...) {
   TH1* h = new TH1F(...);

   return h;
}

Advantage: later on, you can easily change TH1F to TH1D by just changing one character in the whole program. Also your functions will work for any type of histogram just fine.

[Danilo]

Hi,

a correct version of your function:

TH1F* photon_received(char* inputfile){
auto h = new TH1F(“h”, “photon_received/event”, 20, 0.0, 20.0);
{a for loop filling the pointer h…}
h->Draw();
return h;
}

Cheers,
D

[jason777777777]

Thanks! It helps a lot!

[jason777777777]

Thanks for correcting my code! I understand it now.
Best,

[jason777777777]

Thanks, I take your method and it works!
Best,