C++ Can friends classes access all of the members of its base class?

Question

My understanding was that a friend class can access all of the members (including data members) of the base. However, with this code:

class Animal {                                                                                                                                                                                            
  string _name;                                                                                                                                                                                           
  Animal(){};                                                                                                                                                                                             
  Animal(const string & n, const string & t, const string & w); 
  friend class Duck;                                                                                                                                                                                      
};                                                                                                                                                                                                        

Animal::Animal(const string & n) : _name(n) {                                                                                                     
}                                                                                                                                                                                                         


class Duck: public Animal {                                                                                                                                                                               
public:                                                                                                                                                                                                   
  Duck(const string n) : Animal(n){};                                                                                                                                                    
};                                                                                                                                                                                                        


int main(int argc, char *argv[])                                                                                                                                                                          
{                                                                                                                                                                                                         
  Duck donald("Donny");                                                                                                                                                                                   
  printf("The donlad ran %s\n", donald._name.c_str());                                                                                                                                                 
  return 0;                                                                                                                                                                                               
}

I get error: '_name' is a private member of 'Animal'

Why can't the friend class Duck access all the members of the base class Animal?

Answer 1

The error is where you call printf("The donlad ran %s\n", donald._name.c_str()); in main

You can't access _name via a class instance (donald in this case) because _name is private. _name is accessible from within the Duck class because of the friend designation, but is not accessible in main

Answer 2

1. friend has nothing to do with inheritance.

2. You get the error because main(), not Duck, is the one trying to access the private _name member of Animal. Making Duck a friend of Animal grants access to Duck's own methods, not to main().