class Base {
public:
    int x;
protected:
    int y;
private:
    int z;
};
// 保护继承Base类
class Derived : protected Base {
public:
    void show() {
        // 派生类内部访问逻辑
    }
};
int main() {
    Derived d;
    // 类外访问逻辑
    return 0;
}