I think it is not very complicate for each separate case:
- Write your C++ class to create (or read from ROOT file)
ROOT TH... objects (anyway one has to right this piece of
code hasn't he?)
- Insert a few extra lines to call from that code HBOOK<n>,
HFILL(...) etc. and get your HBOOK histograms. You may
regard using CFortran package from DESY for example.
Note: It is assumed one has the CERNLIB libraries around
----
- Compile everything to make a ROOT custom share library.
- share result with ROOT-users community via roottalk list.
I wonder someone from our list did this already and may report
his/her result as well.
Hope this helps,
Valery