Reading data from custom classes written in TTree

[rhaake]

Dear experts,

I would like to read data from a TTree that contains objects of a custom class (inherited from TObject) without knowing the exact definition of that class. If possible, I would like to avoid reimplementing the class that was used for the tree creation since I do not have this part of the code under control.

Also without knowing the class, ROOT can obviously access the data – using a TBrowser, i see all the members I am interested in as branches.

However, the following example code does not work:

  TFile* inFile = new TFile("./myTree.root", "READ");
  TTree* inTree = inFile->Get("tree");

  Float_t vertexZ = 0;
  inTree->SetBranchAddress("VertexZ", &vertexZ);
  inTree->GetEntry(0);
  std::cout << vertexZ << std::endl;

VertexZ is the correct branch name, and there is no error message. But the value of vertexZ is just not reset when using GetEntry(0) (or other tree indices).

Am I missing something? Is “custom-class-agnostic” reading of trees possible at all?
NB: I am using ROOT5.

Thanks & best,
Rudiger

[Wile_E_Coyote]

Header files for Trees

“Most recent” documentation about how to generate and use an “analysis skeleton”: TTree::MakeClass (see also “ROOT User’s Guide” → “Trees” → “Using TTree::MakeClass”) TTree::MakeSelector (see also “ROOT Primer” → “File I/O and Parallel Analysis” → “N-tuples in ROOT” → “For the advanced user: Processing trees with a selector script” and “ROOT User’s Guide” → “Trees” → “Using TTree::MakeSelector” and “ROOT User’s Guide” → “Example Analysis”) TTree::MakeProxy ROOT::RDataFrame (uses the T…

[rhaake]

Thanks for the answer!

So from the linked topic I understand that I really need the class definition (extracted via MakeClass or directly). I cannot just access the branches, right?

So probably I cannot circumvent to implement a local copy/class skeleton in my code.

Best,
Rudiger

[Wile_E_Coyote]

If you don’t know how to deal with your tree, see how various flavours of automatically generated “analysis skeletons” deal with it.

Moreover, you may be interested in: TFile::MakeProject