Hi Pierre-Luc,
Objects of class that do not inherit from TNamed are not retrievable by
name.
Technically this is because gDirectory use a hash table and that the hash
value on an object is calculated base on the name ONLY for a TNamed object.
Hence the hash value of 'TMatrixD' and of mymatrix are different and thus it
does not find the object.
Cheers,
Philippe.
-----Original Message-----
From: owner-roottalk@pcroot.cern.ch
[mailto:owner-roottalk@pcroot.cern.ch]On Behalf Of Pierre-Luc Drouin
Sent: Wednesday, August 13, 2003 9:16 AM
To: Rene Brun
Cc: roottalk@pcroot.cern.ch
Subject: Re: [ROOT] TDirectory::Get() with objects in memory
HI,
Here is an example.
root [0] TObjString *mystr=new TObjString("mystr")
root [1] gDirectory->Add(mystr)
root [2] TMatrixD *mymatrix=new TMatrixD(1,1)
root [3] gDirectory->Add(mymatrix)
root [4] gDirectory->ls()
TROOT* Rint The ROOT of EVERYTHING
OBJ: TObjString mystr Collectable string class : 0 at: 0x8e5ac60
OBJ: TMatrixD TMatrixD Matrix class (double precision) : 0 at:
0x8ba8e00
root [5] mystr->GetName()
(const char* 0x8e5ac8c)"mystr"
root [6] gDirectory->Get("mystr")
(class TObject*)0x8e5ac60
root [7] mymatrix->GetName()
(const char* 0x8e5ae4c)"TMatrixD"
root [8] gDirectory->Get("TMatrix")
(class TObject*)0x0
Thank you!
Pierre-Luc Drouin
On Wed, 13 Aug 2003, Rene Brun wrote:
> Pierre-Luc,
>
> I cannot reproduce this problem. Please send a short script.
>
> Rene Brun
>
> Pierre-Luc Drouin wrote:
> >
> > Hi,
> >
> > There is something I don't understand with TDirectory::Get(). Suppose
I've
> > a
> > TNamed object and a object from a class that I've derived from
> > TNamed. Both objects have been added in gDirectory using
> > gDirectory->Add(). The object names are respectively "tnamed" and
> > "tnamedd". Why do I get this result:
> >
> > gDirectory->Get("tnamed") returns a pointer to the TNamed object
> > gDirectory->Get("tnamedd") returns a NULL pointer (not a pointer to the
> > TNamed derived object)
> >
> > If both objects are written a TKey into gDirectory, I get valid pointers
> > with the 2 lines
> >
> > I get also this problem with ROOT classes. With a TObjString object, I
get
> > a valid pointer. With a TMatrixD object, I get a NULL
> > pointer.
> >
> > TDirectory::FindObject() behaves the same way (with objects in memory of
> > course)
> >
> > Thank you!
> >
> > Pierre-Luc Drouin
>
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