Re: Possible encapsulation issue

=?ISO-8859-1?Q?Daniel_Kr=FCgler?= <>
Tue, 14 Sep 2010 08:15:51 CST
On 14 Sep., 01:05, Amit Mishra <> wrote:

Consider this program.


Output: Derived foo()
So it is possible to access a private data member this way.

This is not an oversight, but an intended design choice.
Virtual functions are always observable and the overriding
mechanism is immune against access control. Even a
*private* virtual function in the base class will be overriden
by a corresponding function signature in the derived class
as in the following variation of your example:

#include <iostream>

class Base {
   virtual void foo() { std::cout << "Base foo()\n"; } // Private here!
   void bar() { foo(); }

class Derived : public Base {
   void foo() { std::cout << "Derived foo()\n"; } // OK: Final

int main()
   Derived d;
   Base* bp = &d;
   bp->bar(); // OK: Writes "Derived foo()\n"

Additional to that, virtual functions in templates also
have special rights: An implementation is allowed to
instantiate each virtual function implementation, even
if it is not used - in contrast to all other member
functions of a class template. This means that every
declared virtual function *must* be defined, *unless*
it is a pure virtual functions.

HTH & Greetings from Bremen,

Daniel Kr=FCgler

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