Hi Stefan, You must write back the modified and new objects to the file. The file mmust be opened in update mode. To write back the modified/new objects, two possibilities 1- write each of them individually to the file, eg pt_sig_teamlt18.Write(); 2 -write all objects to the file with file->Write(); In your case, option 2 is probably the best. Rene Brun Stefan Stonjek wrote: > > Hello Root Users, > > I have a problem with writing a histogram to a specific file. > > It is no problem to read the allready existig histos in this program. They > are already filled in the same program and the "print" command clearly > indicated that the new histogram contains usefull date. But these data > does not end up in the file. > > Here is the code in question. It is just an excerpt from a much longer > program with many subroutines. > > TH1F *pt_gcc_sig_etamlt18 = (TH1F*)hfile->Get("pt_gcc_sig_etamlt18"); > TH1F *pt_wcc_sig_etamlt18 = (TH1F*)hfile->Get("pt_wcc_sig_etamlt18"); > hfile->cd(); > TH1F pt_sig_etamlt18 = ( *pt_gcc_sig_etamlt18 - *pt_wcc_sig_etamlt18); > pt_sig_etamlt18.SetName("pt_sig_etamlt18"); > pt_sig_etamlt18.SetDirectory(hfile); > pt_sig_etamlt18.Print("all"); > > Mayby it is just a stupid mistake but I hope someone is able to help me. > > Tschuess > Stefan > > ********* Stefan Stonjek ********* > ***** DESY / ZEUS ***** > ***** Stefan.Stonjek@desy.de ***** > ********* Tel.: +49-40-8998-3159 *********
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