Add functionality to a pure virtual function in C++?

October 20, 2022

I wish to have a pure virtual function, but I need to guarantee that all implementations of it include some bookkeeping.

Here is a workaround that achieves what I want, but it is clunky.

Is there a better approach? If not, is there a naming convention for a function like actually_do_it()?

class A
{
public:
  virtual void do_it() final
  {
    bookkeeping();
    actually_do_it();
  }

protected:
  virtual void actually_do_it() = 0;

private:
  void bookkeeping() {}
};

class B : public A
{
  void actually_do_it() {}
};

...

B b;
b.do_it();

>Solution :

Is there a better approach? If not, is there a naming convention for a function like actually_do_it()?

"better" is purely subjective unless you define what "better" means. You approach is widely accepted and known as the Template Method Pattern (see eg https://en.wikipedia.org/wiki/Template_method_pattern).

I have seen it more commonly used when a method consists of several steps and the derived classes can customize the individual steps, but your use case is just as valid.