带有访问修饰符的 C++ 继承

Question

我有这段代码

    #include <iostream>
    using namespace std;
    class Polygon
    {
        public:
            int publicmemberPolygon;
        private:
            int privatememberPolygon;
        protected:
            int protectedmemberPolygon;
   };

    class Square : public Polygon
    {
    public:
        int Getter();
     };
    int Square::Getter()
    {
    return privatememberPolygon;
    }

    int main()
    {
    }

问题是，为什么 privatememberPolygon 无法访问？是不是，当你有一个派生类时，它的所有成员/函数都被复制了？谢谢

Answer 1

不，当您从基类公开派生时，派生类只能访问其 public 和 protected 成员。您还可以阅读此 FAQ .

看这个例子:

class Base
{

public:
    void setPrivate(int p) 
    {
        m_private = p;
    }

public:
    int m_public;
protected:
    int m_protected;
private:
    int m_private;
};

class Derived : public Base
{
public:
    void f()
    {
        m_public = 0; // Can access public member of base class
        m_protected = 0; //Can access protected member of base class
        m_private = 0; //Compiler error- Can not access private member of base class
    }
};

int main() {

    Derived d;
    d.setPrivate(10); //m_private is still part of the derived class. Hence can call setPrivate
    return 0;

}