derived_base.cpp

#include <iostream>

using namespace std;

class Base1 {
    public:
        Base1():value(10) {}
        virtual ~Base1() {}
        void test1() { cout << "Base test1..." << endl; }
    protected: // 保护
        int value;
};
// 默认为私有继承
class Derived1 : Base1 {
    public:
        void test2() { cout << "value is " << value << endl; }
};

class Base {
    public:
        Base():value(20) {}
        virtual ~Base() {}
        void test1() { cout << "Base test1..." << endl; }
    private:  //私有
        int value;
};

/**
 * 子类对父类成员的访问权限跟如何继承没有任何关系，
 * “子类可以访问父类的public和protected成员，不可以访问父类的private成员”——这句话对任何一种继承都是成立的。
 *
 */
class Derived : Base {
    public:
        using Base::value;
        void test2() { cout << "value is " << value << endl; }
};


int main() 
{
    Derived1 d1;
    d1.test2();

    Derived d;
    d.test2();
    return 0;
}