RE: Question on derived class?

RE: Question on derived class?

[Pradip Singh]

Hi All,

   It is possible to access a->reset() by runtime polymorphism concept in c++. But in ur code the assignment A *a = b is wrong. It should be A *a = &b; But I donot know what u mean by pure virtual class. If it is a class contianing some pure virtual methods then it is called abstract class. And remember to define the pure virtual functions in A in b. Otherwise B will also become abstract class and u cannot create its object. So the very statement static B b; will start throwing compilation error.

But this is not the right forum to ask such question. Find some other C++ forum.

thanks and regards,
Pradip

-----Original Message-----
From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org]On
Behalf Of Ishwar Rattan
Sent: Friday, November 19, 2004 5:40 AM
To: gcc-help@gcc.gnu.org
Subject: Question on derived class?



Assume that A is pure virtual class with some public
methods.

B is derived from A

Class B : virtual A {
public:
     // all methods of A are defined here +
     A new method is also defined (here only)
     -- call it reset()
protected:
     // ...
};

Now B is initiated as

static B b;
A *a = b;

Is it possible to access b.reset() using a->reset()?

-ishwar

RE: Question on derived class?

[Eljay Love-Jensen]

Hi Lyle,

 >How is that possible, since 'A' does not have a reset method in it?

It is possible.  By putting the virtual reset() method in the A interface 
class.

(Obviously, I didn't go into details as to the implementation.  Ishwar's 
question only asked if it was possible or not.)

 >Shouldn't only methods defined in 'A' be able to be called on 'a'?

Correct.  :-)

Sincerely,
--Eljay

RE: Question on derived class?

[lrtaylor]

How is that possible, since 'A' does not have a reset method in it?  At
the time he tries to call a->reset(), the compiler won't know the method
can be called.  Shouldn't only methods defined in 'A' be able to be
called on 'a'?

Thanks,
Lyle


-----Original Message-----
From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org] On
Behalf Of Eljay Love-Jensen
Sent: Thursday, November 18, 2004 5:20 PM
To: Ishwar Rattan; gcc-help@gcc.gnu.org
Subject: Re: Question on derived class?

Hi Ishwar,

Your question is a general C++ question, and off-topic for this forum.

 >Is it possible to access b.reset() using a->reset()?

Yes.

HTH,
--Eljay

Re: Question on derived class?

[Eljay Love-Jensen]

Hi Ishwar,

Your question is a general C++ question, and off-topic for this forum.

 >Is it possible to access b.reset() using a->reset()?

Yes.

HTH,
--Eljay

Question on derived class?

[Ishwar Rattan]

Assume that A is pure virtual class with some public
methods.

B is derived from A

Class B : virtual A {
public:
     // all methods of A are defined here +
     A new method is also defined (here only)
     -- call it reset()
protected:
     // ...
};

Now B is initiated as

static B b;
A *a = b;

Is it possible to access b.reset() using a->reset()?

-ishwar