Re: [ROOT] Constructing an object with TClass() information MORE INFO

From: Fons Rademakers (Fons.Rademakers@cern.ch)
Date: Sat Nov 24 2001 - 04:54:33 MET


Hi Volker,

  better than using directly gInterpreter use gROOT methods:
   gROOT->ProcessLineFast()
is the equivalent of the Calc() method with in addition some
protections to make sure the environment is correctly setup.
Idem for gROOT->ProcessLine().

Cheers, Fons.


On Fri, Nov 23, 2001 at 10:43:34AM +0000, Rene Brun wrote:
> Hi Volker,
> 
> Thinking a bit more to your problem, there is a good solution to it
> in ROOT 3.02/04 (thanks to Philippe).
> Instead of using the function ProcessLine, use Calc.
> Example
> 
> TObject *obj=(TObject*)gInterpreter.Calc("new TH1F(\"h\",\"h\",100,-3,3)")      
> obj->Draw();
> 
> Calc returns the result of the query as a Long_t. You just have to cast it
> to the correct type, or simply a TObject* if you like.
> 
> Rene Brun
> 
> Rene Brun wrote:
> > 
> > Hi Volker,
> > 
> > Following a mail from Axel, I just realize that I misunderstood your question.
> > 
> > Why do you want to call TClass::New to create a new object ?
> > Why don't you call directly the class constructor?
> > 
> > In case, you want to create an object when you know only the name ot its class
> > (could be what you try to do?), you can use the interpreter ProcessLine,
> > Example:
> >    gInterpreter.ProcessLine("new TH1F(\"h\",\"h\",100,-3,3)")
> > will create a new TH1F object. In this particular case, you can retrieve
> > a pointer to the created object via gDirectory->Get("h"): the TH1F constructor
> > adding automatically a reference to the object in the list of objects
> > of the current directory.
> > You can modify your constructor to automatically register itself to some
> > collection.
> > 
> > Rene Brun
> > 
> > Volker Hejny wrote:
> > >
> > > Hallo,
> > >
> > > if I have a class name as a string value at run time, it is possible
> > > to construct a new object of this class using TClass::New(). That
> > > way the standard constructor is called. Is there any way to call
> > > a different constructor with a given argument?
> > >
> > > Best regards,
> > > Volker
> > >
> > > --
> > > Dr. Volker Hejny                Tel: 02461/616853                      **
> > > Institut f. Kernphysik          Fax: 02461/613930                     **
> > > ---------------------------------------------------------------- **  ** ---
> > > Forschungszentrum Juelich GmbH, D-52425 Juelich                    **

-- 
Org:    CERN, European Laboratory for Particle Physics.
Mail:   1211 Geneve 23, Switzerland
E-Mail: Fons.Rademakers@cern.ch              Phone: +41 22 7679248
WWW:    http://root.cern.ch/~rdm/            Fax:   +41 22 7679480



This archive was generated by hypermail 2b29 : Tue Jan 01 2002 - 17:51:09 MET