I have a class A, which have a field val declared as private. I want to declare a class B, that inherit from A and have an access to val. Is there a way to do it on C++?
I want to do it because I need to overload some functions of A, without changing A code at all.
Thanks.
Quick answer: You don't. Thats what the protected key-word is for, which you want to use if you want to grant access to subclasses but no-one else.
private means that no-one has access to those variables, not even subclasses.
If you cannot change code in A at all, maybe there is a public/protected access method for that variable. Otherwise these variables are not meant to be accessed from subclasses and only hacks can help (which I don't encourage!).
Private members of a base class can only be accessed by base member functions (not derived classes). So you have no rights not even a chance to do so :)
class Base
- public: can be accessed by anybody
- private: can only be accessed by only base member functions (not derived classes)
- protected: can be accessed by both base member functions and derived classes
Well, if you have access to base class, you can declare class B as friend class. But as others explained it: because you can, it does not mean it's good idea. Use protected members, if you want derived classes to be able to access them.
It is doable as describe in this Guru of the Week - GotW #76 - Uses and Abuses of Access Rights. But it's should be considered a last resort.
You need to define it as protected. Protected members are inherited to child classes but are not accessible from the outside world.
来源：https://stackoverflow.com/questions/8241462/access-private-members-in-inheritance