GetValue for TLeafF and TLeafI with variable-sized arrays

From: Philip Rodrigues <p.rodrigues1_at_physics.ox.ac.uk>
Date: Wed, 26 Aug 2009 13:51:30 +0100

Hi roottalk,
I'm trying to access the values of variable-sized arrays using TLeaf::GetValue, with code like the following:

  TTree* t = [[ some tree ]];
// branch "dir" has title "dir[nring][3]/F"
// where "nring" has type "nring/I"

  TBranch* b_dir=t->FindBranch("dir");
  TLeaf* l_dir=t->FindLeaf("dir");

  dir->GetEntry(0);
// Should get dir[0][1] in the 0th entry
  l_dir->GetValue(1);

I noticed that this fails for "dir", which is a float variable, but succeeds for integer variables. I found the necessary workaround, which is to do:

l_dir->GetLeafCount()->GetBranch()->GetEntry(0);

before dir->GetEntry(0), but I'm wondering if I'm misunderstanding how this is supposed to work. Should it be necessary to put this extra line in?

Thanks,
Philip

PS The reason it *does* work for integer variables is because TLeafI::ReadBasket looks like:

   if (!fLeafCount && fNdata == 1) {

       b >> fValue[0];
    } else {

       if (fLeafCount) {
/**/     Long64_t entry = fBranch->GetReadEntry();
/**/     if (fLeafCount->GetBranch()->GetReadEntry() != entry) {
/**/        fLeafCount->GetBranch()->GetEntry(entry);
/**/     }
          Int_t len = Int_t(fLeafCount->GetValue());
          if (len > fLeafCount->GetMaximum()) {
             printf("ERROR leaf:%s, len=%d and 
max=%d\n",GetName(),len,fLeafCount->GetMaximum());
             len = fLeafCount->GetMaximum();
          }

    [ ... ]

so it does the GetEntry on the necessary branch. The corresponding function in TLeafF lacks the lines I've marked with a /**/ Received on Wed Aug 26 2009 - 14:51:34 CEST