Reading vectors from a tree

General Chat
1

Hi! I am a begginer using trees, I have .root file with a lot of variables, I have just declared all of them in my .C document, I declared them like:

vector<double> *Station=0;

after that I do:

t->SetBranchAddress(“Station”,&Station);

I want to work with this variable as a vector, so I do:
Double_t *sig = new Double_t [n]; //n is the number of entries in the tree
sig =Station->data();

After that I do a cout to check that everything is correct but it isn’t because it doesn’t show me nothing.

Could you tell me where is the problem?
Thank you very much.

2

Do you mean you want to retrieve a tree variable in a C++ vector ?
If that’s the case the following tutorial may help you:
https://root.cern/doc/master/treegetval_8C.html

3

Thank you very much!!
Variables 0, 5 and 6 are x, y and z? Why they are that name??

4

GetVal works with Variables Number.

5

Please note that TTree::GetVal retrieves the results of the most recent TTree::Draw and nothing else.

Something like this should work:

vector<double> *Station = 0;
t->SetBranchAddress("Station", &Station);
Long64_t n = t->GetEntries();
for (Long64_t i = 0; i < n; i++) {
  t->GetEntry(i);
  ULong_t nsig = Station->size(); // MUST be done for every tree entry
  double *sig = Station->data(); // MUST be done for every tree entry
  for (ULong_t j = 0; j < nsig; j++) {
    std::cout << i << " : " << j << " : " << sig[j] << std::endl;
  }
}
t->ResetBranchAddresses(); // disconnect from local variables
delete Station; // cleanup
6

Yes, it is interesting if you want to get the values corresponding to combination of variables.