Re: can I override private functions?

From:

Rolf Magnus <ramagnus@t-online.de>

Newsgroups:

comp.lang.c++

Date:

Tue, 13 Mar 2007 16:53:09 +0100

Message-ID:

<et6hd5$77j$02$1@news.t-online.com>

mlimber wrote:

On Mar 13, 11:04 am, "Nick Keighley"
<nick_keighley_nos...@hotmail.com> wrote:

I take it this is wrong:-

class Direct_draw
{
public:
    Direct_draw ();

    virtual ~Direct_draw ()
    {}

private:
    virtual void draw_primary () = 0;

};

class Dd_animation: public Direct_draw
{
public:
    Dd_animation()
    {}

    ~Dd_animation()
    {}

private:
    virtual void draw_primary ()
    {}

};

Direct_draw::Direct_draw ()
{
    draw_primary();

}

int main (void)
{
     Direct_draw* animation = new Dd_animation();
         return 0;

}

it gives a linker error for draw_primary()

You can certainly override private virtual functions; you just can't
call virtuals from the ctor:

http://www.parashift.com/c++-faq-lite/strange-inheritance.html#faq-23.5

The FAQ claims that dynamic binding isn't happening in constructors and
destructors, but that's actually not true. Dynamic binding does happen, but
only up to the class the constructor/destructor belongs to. Consider the
following example:

#include <iostream>

class Base
{
public:
    void test() { virtual_function(); }
    virtual void virtual_function() { std::cout << "Base\n"; }
};

class Derived : public Base
{
public:
    Derived() { test(); }
    virtual void virtual_function() { std::cout << "Derived\n"; }
};

int main()
{
    Derived d;
}

Without dynamic binding, this would print "Base", but it does
print "Derived".