Re: Virtual function behaviour

From:
"Victor Bazarov" <v.Abazarov@comAcast.net>
Newsgroups:
comp.lang.c++
Date:
Tue, 3 Apr 2007 17:55:31 -0400
Message-ID:
<euuigl$a2r$1@news.datemas.de>
dragoncoder wrote:

I was just playing around wrote this code.

sundev1:/home/ptiwary/rnd $ cat a1.cpp
#include <iostream>

using namespace std;

class Base
{
   public:
       virtual void foo() { cout << "In Base::foo()" << endl; bar();}
   private:
       void bar() { cout << "In Base::bar()" << endl; }
};

class Der1: public Base
{
   public:
       virtual void foo() { cout << "In Der1::foo()" << endl; bar();}
   private:
       void bar() { cout << "In Der1::bar()" << endl; }
};

class Der2: public Base
{
   public:
       virtual void foo() { cout << "In Der2::foo()" << endl; bar();}
   private:
       void bar() { cout << "In Der2::bar()" << endl; }
};

int main()
{
   Base* b1 = new Base();
   Base* b2 = new Der1();
   Base* b3 = new Der2();

   b1->foo();
   b2->foo();
   b3->foo();

   return 0;
}

sundev1:/home/ptiwary/rnd $ g++ a1.cpp
sundev1:/home/ptiwary/rnd $ ./a.out
In Base::foo()
In Base::bar()
In Der1::foo()
In Der1::bar()
In Der2::foo()
In Der2::bar()

I have 2 questions regarding this.

1. Is the behaviour correct? Because someone told me I need to make
bar() also virtual to get the effect.


No, the 'bar' resolved "statically" (as 'this->bar') in each of the
'foo' functions.

2. What is the deal with private virtual functions? Even if I make
bar() virtual, as its private, it won't be accessible from the derived
classes Der1 and Der2 so it does not make any sense having private
virtual functions. Am I right?


Access specifiers and virtuality are orthogonal. IOW, it does not
matter what access specifiers virtual functions have to establish
which of them overrides which.

V
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