C++: inheritance or class member for C struct?

Question

I have a plain old C struct:

struct eggplant {
    double *ptr1;
    double *ptr2;
    ... // many more
}

and a function that manages the allocation the memory pointed to by the pointers, and returns a new eggplant instance:

struct eggplant *create_eggplant(int n);

The above function allocates a chunk of memory (including space for the newly created struct) and distributes it to the pointers.

---

I want to extend struct eggplant in C++11. I could do that by keeping a pointer to the struct as a

member:

class EggPlant {
    ...
    private :
        struct eggplant *plant;
}

or I could try via

inheritance:

class EggPlant : private struct eggplant {
    ...    
}

The first option allows me to use the create_eggplant function. However, the second option looks more straightforward from a conceptual point of view (the class EggPlant is an eggplant, it doesn't have one).

I tried

this = create_eggplant(...);

in the constructor but that does not work for the obvious reason that you cannot overwrite a pointer to a class that you are constructing (lvalue required).

Can I inherit the struct but still use my create_eggplant function in some useful way? Or, is it anyway better to keep a pointer to the struct?

Answer 1

Your choice to have struct eggplant *create_eggplant(int n); manage its own memory is in conflict with C++ inheritance. Inheritance also implies management of the location of the base object.

If you changed your C function to return a copy:

struct eggplant create_eggplant(int n);

You could also inherit from that class:

class EggPlant : private eggplant {
    EggPlant(int n) : eggplant{ create_eggplant(n) }
    {
    }
    ...    
};

Answer 2

No, you would need a new function if you wish to inherit. If you must use the existing function a member is the best you will be able to manage.