[ROOT] TTree::MakeClass with added iterators.

From: Clark McGrew (clark.mcgrew@sunysb.edu)
Date: Sat Jul 12 2003 - 04:44:57 MEST 

Hello,

(I've sent this message a couple times now, and so far it hasn't shown
up in the roottalk archives.  I assume it's getting cut by some spam
filter, so I've removed the attached code. I apologize if it you are
getting several copies) 

I often find myself with a TTree that I would like to use MakeClass (or
similar) to start an analysis, but there is a problem when the TTree
definition changes and I need to regenerate the "loop" file.  Any new
MakeClass will stomp on my Loop code, unless I've been careful and
copied/renamed my file.  However, it occurs to me that the
problem can be solved very simply with an iterator.

root [0] TTree *t = GetATree();
root [1] t->MakeClass("TTreeClass");
root [2] .L TTreeClass.C
root [3] TTreeClass dst;
root [4] TTreeClass::iterator it;
root [5] for(it=dst.Begin();it!=dst.End();++it) cout << it->nev << endl;

which is rather simpler and more intuitive (to me) than the only other
solution I've run across (compare lines [4] and [5] below). 

root [0] TTree *t = GetATree();
root [1] t->MakeClass("TTreeClass");
root [2] .L TTreeClass.C
root [3] TTreeClass dst;
root [4] int i;
root [5] for(i=0;;++i) {
   if (dst.LoadTree(i)<0) break;
   dst.GetEntry(i);
   cout << dst.nev << endl;
}

I've put modified code at:

<http:://ale.physics.sunysb.edu/~mcgrew/TTreePlayer.cxx.gz>

I made the patch against Version 1.126 from CVS.  I've been using the
code generated by this patch for a while, and it seems to be working
pretty well.  

Sincerely,
Clark
-- 
Clark McGrew	                Univ. at Stony Brook, Physics and Astronomy
<clark.mcgrew@sunysb.edu>	631-632-8299

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