RE: [ROOT] Derived class in a tree

From: Philippe Canal (pcanal@fnal.gov)
Date: Thu Jul 26 2001 - 16:26:47 MEST 

Hi Mike,

Following your code I was able to reproduce the message:
   "Error in <TClass::New>: cannot create object of class EBlahType"

However in my case, the file was still properly produced.  Scan worked
nicely.  

One thing that I did differently is to have Base derived from TObject.

I would need more information in order to reproduce and understand 
the problem.

Cheers,
Philippe.


-----Original Message-----
From: owner-roottalk@pcroot.cern.ch
[mailto:owner-roottalk@pcroot.cern.ch]On Behalf Of Michael Alan Kordosky
Sent: Thursday, July 26, 2001 2:20 AM
To: ROOTtalk Mailing List
Subject: [ROOT] Derived class in a tree



Hi,

Is the following expected to work (in a tree)?

An (abstract) base class with no data members and a derived class with
basic types + an enum:

class Base{
	/* ... */
	ClassDef(Base, 0)
};

enum EBlahType {kA = 0, kB};

class Derived : public Base{
	/* ... */
	EBlahType fBlahType;
	ClassDef(Derived, 1)
};



LinkDef:

#ifdef __CINT__
/*
link offs
*/
#pragma link C++ Base+;
#pragma link C++ enum EBlahType+;
#pragma link C++ Derived+;
#endif

I am having two problems:

First:
When writing Derived to a tree (via a macro), I get an error message of
the form:

"Error in <TClass::New>: cannot create object of class EBlahType"

The interpreter tab completes EBlahType and knows the right enumeration
for its constants.

Second:
/* Get TTree* t from a file */
root [5] t->Scan();
Error in <TObjArray::At>: index -2 out of bounds (size: 16, this:
0x0866e5c0)

If I give Scan() specific arguments, it seems to work. The enum type has
the correct values.  Could the base class be causing this problem?  I
notice that it is a branch of my tree, and actually takes up a suprising
amount of space, so perhaps I am doing something wrong.

Any ideas/advice?

Mike Kordosky
-- 
Graduate Research Assistant  // High Energy Physics Lab
kordosky@hep.utexas.edu     // University of Texas at Austin
kordosky@fnal.gov	   //
ph: (512) 471-8426 (RLM Lab, Office)
    (512) 475-8673 (ENS Lab)

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