Question on saving histograms to TFile

ROOT
1

If I have to create histograms first before I create TFile, how can I save the histograms to the TFile created later?
Thank you very much!

2

You can write the list of histograms from any existing directory in memory
to the new file, via
mydir->GetList()->Write();
If mydir is the default directory in memory (gROOT), do
gROOT->GetList()->Write();

You can list what you have in mydir (gROOT) with
mydir->GetList()->ls();

Rene

3

Thank you very much! Now I am ablle to save histograms to the new file.
But I have one more question: I think GetList() will get all objects in the memory. I also have some TCutG objects and normal C++ objects in memory. Is it possible to specify the class type so that I can only get histograms? But I don’t want to get histograms one by one because I have too many histograms to get.

4

If you want to write a subset of the objects in the mydir->GetList(), you can do something like:

TIter next(mydir->GetList()); TObject *obj; while ((obj=next())) { if (obj->InheritsFrom("TGraph")) continue; //skip all TGraph/TCutg obj->Write(); }
Rene