12.3 Access Control

访问控制

• Public members
  • Accessible anywhere
• Private members
  • Only accessible to the members and friends of that class ```cpp class Person { private: int n; // private member public: // this->n is accessible Person() : n(10) {} // other.n is accessible Person(const Person& other) : n(other.n) {} // this->n is accessible void set(int n) {this->n = n;} // this->n and other.n are accessible void set(const Person& other) {this->n = other.n;} };

- Protected members
   - Accessible to the members and friends of that class
   - Accessible to the members and friends of the **derived **class 
```cpp
class Base 
{
  protected:
    int n;
  private:
    void foo1(Base& b)
    {
        n++; // Okay
        b.n++; // Okay
    }
};
class Derived : public Base 
{
    void foo2(Base& b, Derived& d) 
    {
        n++; //Okay
        this->n++; //Okay
        //b.n++; //Error. 
        d.n++; //Okay
    }
};

// a non-member non-friend function 
void compare(Base& b, Derived& d)
{
    // b.n++; // Error
    // d.n++; // Error
}

Public Inheritance

• Public members of the base class
  • Still be public in the derived class
  • Accessible anywhere
• Protected members of the base class
  • Still be protected in the derived class
  • Accessible in the derived class only

• Private members of the base class

  • Not accessible in the derived class

    Protected Inheritance

• Public members and protected members of the base class

  • Be protected in the derived class
  • Accessible in the derived class only

• Private members of the base class

  • Not accessible in the derived class

    Private Inheritance

• Public members and protected members of the base class

  • Be private in the derived class
  • Accessible in the derived class only
• Private members of the base class
  • Not accessible in the derived class