class A { protected: //改成private会报错: "A::numX" (已声明 所在行数 : 10) 不可访问 int numX = 100; }; class B: public A { public: void assign(void) { numY = numX; } int getY(void) { return numY; } private: int numY = 0; }; int main(int argc, char *argv[]) { B b; printf("numY = %d\n", b.getY()); b.assign(); printf("numY = %d\n", b.getY()); system("pause"); return 0; }
运行结果: