Hi Stanislas, It is likely that your branch "Ntrk" contains more variables than just an integer. In your case, you overwrite your program by reading the branch variables behind the variable "Int_t nt". If you have more variables, you should define a C struct or a class or use MakeClass such that all variables in the branch are read correctly into the struct. Rene Brun On Fri, 26 Jul 2002, Stanislav NESTEROV wrote: > > Hello Fons, > > Recently I've tried to read some N-tuples via > THbookFile+THbookTree+THbookBranch classes but it was not so easy. > > While I was using only "Draw" functionality all seem to be OK, but when > I've tried to do some readings of certain branches of N-tuple I've > got into a big trouble: I can not do this at ALL: > > So from the beginning: > > > __________________________________________________________________ > Content of my N-tuple: > > ===> Directory : //lun10 > 94 (N) Gamma Gamma Ntuple > 9001 (1) NTRK > 9002 (1) E?BGO! > 9003 (1) E?HCAL! > 9004 (1) E?BGO+HCAL! > 9011 (1) NTRK > 9012 (1) E?BGO! > 9013 (1) E?HCAL! > 9014 (1) E?BGO+HCAL! > 9015 (1) InTEC and OuterTEC TRG > 9099 (1) number of events. > > root [0] gSystem->Load("libHbook.so"); > root [1] THbookFile f("/l3/l3data/99/ggntp/cc01jurg.ntp"); > root [2] tt2=(THbookTree*)f.Get(94) > (class THbookTree*)0x86fca48 > root [3] Int_t nt > root [4] tt2->SetBranchAddress("Ntrk",&nt) > root [5] bran = (THbookBranch*)tt2->GetBranch("Ntrk") > (class THbookBranch*)0x87b4468 > root [6] bran->GetEntry(30) //!!!!!!!!!!!!!!!! > ***** ERROR in HNBUFF : Buffer structure not initialized. : ID= 94 > ***** ERROR in HGNTF : Cannot find Ntuple buffer structure : ID= 94 > (Int_t)0 > ________________________________________________________________________ > > > BUT if I Drawing exatly the same variable ( here "Ntrk") via > > tt2->Draw("Ntrk") > > before getting any entry from this branch then everything is allright. > > So I found in procedure THBookFile::InitLeaves(...) that in case > of empty `TreeFormula* ' argument this procedure just quits. Very strange > solution I think. > > In any case N-tuple initialization (for branches) is failed and one can > only obtain some result if call procedures that using > TTreePlayer::InitLoop with some related formula. > > May be the best solution is slightly change the > THbookTree::InitLeaves()? I really don't know. Or just throw out from > THbookFile::GetEntryBranch call of HGNTF subrouting (in such specific > cases)? > > Best regards > Stanislav. >
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