可见性

比较简单，很好理解，长话短说

#include<iostream>

using namespace std;

class A {
private:
	int x;
protected:
	int y;
public:
	int z;
	A(int x = 0, int y = 0, int z = 0) {
		A::x = x;
		A::y = y;
		A::z = z;
	}
	void print() {
		cout << A::x << endl;
		cout << A::y << endl;
		cout << A::z << endl;
	}
};

class B :public A{
public:
	B(int y, int z) {
		B::y = y;
		B::z = z;
	}
	void print() {
		//cout << B::x << endl; 错误，x是protected，派生类无法访问
		cout << A::y << endl;
		cout << A::z << endl;
	}
};	

int main(void) {
	A test(1, 2, 3);
	test.print();
	B test2(1, 2);
	test2.print();
	//x与y分别是private和protected，不能在类外访问
	//cout << test.x << endl;
	//cout << test.y << endl;
	cout << test.z << endl;
	return 0;
}