为什么我不能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

我有一段时间没有使用 C++，无法弄清楚为什么以下不起作用:

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;
}

编译产生:

错误 C2248:A::num":无法访问类A"中声明的受保护成员

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

派生类不应该访问受保护的成员吗?

Shouldn't protected members be accessible by derived classes?

我错过了什么?

推荐答案

是的，派生类可以访问受保护的成员，但是您正在 main() 函数中访问它，该函数在层次结构之外.如果你在 B 类中声明一个方法并访问 num 就可以了.

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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