为什么无法从派生类的实例访问受保护的成员？ [英] Why can't I access a protected member from an instance of a derived class?

问题描述

我有一段时间没有做过C ++，无法弄清楚为什么后续工作不起作用：

I haven't done C++ in a while and can't figure out why following doesn't work:

class A {
protected:
  int num;
};

class B : public A {
};

main () {
  B * bclass = new B ();
  bclass->num = 1;
}

编译这会产生：

错误C2248：'A :: num'：无法访问在'A'类中声明的受保护成员

error C2248: 'A::num' : cannot access protected member declared in class 'A'

应该不能通过派生类来访问受保护的成员？

Shouldn't protected members be accessible by derived classes?

我缺少什么？

推荐答案

是受保护的成员可以通过派生类访问，但是您正在main（）函数中访问它，这是在层次结构之外。如果你在类B中声明一个方法并访问num，它会很好。

yes protected members are accessible by derived classes but you are accessing it in the main() function, which is outside the hierarchy. If you declare a method in the class B and access num it will be fine.

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