Hi Maurik,
A TChain is a readonly collection of TFiles containing the same TTree
structure. One creates the branches in the TTree, not in TChain.
I would suggest to have a look at the classes THbookFile, THbookTree,
THbookBranch that are wrapper classes to read PAW/Hbook ntuple files
and supporting the query facilities of TTree::Draw. These classes
can give you some ideas to implement your "translation classes".
See:
http://root.cern.ch/root/htmldoc/THbookTree.html
http://root.cern.ch/root/htmldoc/THbookBranch.html
http://root.cern.ch/root/htmldoc/THbookFile.html
http://root.cern.ch/root/htmldoc/THbookKey.html
Note that THbookChain does not exist in the current implementation.
Rene Brun
On 30 Apr 2002, Maurik Holtrop wrote:
> Hello Root,
>
> I am writing a "translation class" that I would like to have mimic the
> behavior of a TChain, so that programs that currently use TChain can use
> my new class to read non-root data directly.
>
> My first try, I made a new class derived from TTree, gave this class
> some branches, and then fill the branches in an over-written GetEntry().
> This mostly seemed to work, however, to get a program to accept this
> "TTree like" object, I need to cast it to a (TChain *). This gives
> problems when the programs calls a method that does not exist in TTree
> (segfault).
>
> Second try I figured I just derive from TChain instead of TTree, and
> since TChain derives itself from TTree, everything should still work.
> Not so.
>
> The following does not work on a TChain:
>
> Int_t *myint = new Int_t();
> TChain *ch = new TChain("CLASEVENT","Test me");
> TBranch *chb = ch->Bronch("HEADER","THEADERClass",&myint);
>
> *** Break *** segmentation violation
>
> BUT:
> TTree *te = new TTree("CLASEVENT","Test me");
> TBranch *chb = te->Bronch("HEADER","THEADERClass",&myint);
>
> No problem.
>
> This puzzles me, since the "Bronch" (or "Branch" for that matter)
> methods are defined only in TTree, and not overwritten in TChain.
>
> Could someone explain how I can initialize branches on a TChain, when
> they are NOT read from a file, and not even connected to a file?
>
> Thank you much,
>
> Maurik Holtrop
>
>
>
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