Re: Implementation of abstract classes

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Sat, 20 Sep 2008 17:12:03 GMT
On 2008-09-20 18:52, Rune Allnor wrote:

On 20 Sep, 18:40, Christian Hackl <> wrote:

Rune Allnor wrote:

1) I would like to prevent users from making instances of
   class base
2) There are no overloaded functions beween the base class
   and the derived classes, so I can not use the usual

   virtual void overloaded_function() = 0;

   in the base class.

As far as I can see, there are two ways to proceed:

1) make some virtual dummy function that the
   derived classes need to implement
2) Hide the constructor of base as protected.

If your base class is going to be used polymorphically, you must declare
its destructor virtual anyway, so you don't need a "dummy" pure virtual
function. Just declare the destructor itself pure virtual:

virtual ~base() = 0

Of course!

This solution takes care of the case I'm working on
right now, but how would one do this if there were
some cleaning up to do on the base class level?

With the above solution one would have to call some
base::cleanup() function in each of the derived
destructors, right?

Just because a function is pure virtual does not mean it cannot be

#include <iostream>

struct Base
  virtual ~Base() = 0
    std::cout << "~Base\n";

struct Derived : public Base
    std::cout << "~D\n";

int main() {
  Derived d;
  return 0;

Erik Wikstr??m

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