具有私有访问说明符的c ++派生类

Question

I have a derived class (class B) from a base class (class A). Class A has a protected virtual function foo() which I want to override and use it as private in derived class.

Class A{
  protected:
   virtual void foo() = 0;
}

I am wondering whether the following

Class B: public Class A
  private:
    virtual void foo();

and

Class B: private Class A
  private:
    virtual void foo();

are the same.

Answer 1

They are not the same. In the first example, B is-an - A , in the second it isn't. So in the first case you can have code such as

void foo(const A& a);

which accepts A and B as arguments. With private inheritance, you could not do that. For example,

A a;
B b;
foo(a); // OK with private and public inheritance
foo(b); // OK only with public inheritance, i.e. B is an A.

Answer 2

No, your two cases are not the same.

In the second case class B can't be casted to class A , because a private base class is hidden. in this aspect would get the same behavior as if class A would be a member of class B .

Answer 3

两者都不相同在公共继承类A中，foo（）将被保护为类B中的成员。在私有继承中，类B仅可以访问类A的公共成员，因此在类B中将不会出现任何类A的foo（）。 。