c++ - c++调用基类的ostream友元函数

Question

所以，我有两个类:

class Base {
    private:
        int number;
    public:
        friend ostream & operator<<(ostream & output, const Base &n);
}

ostream & operator<<(ostream & output, const Base &n) {
    output<<n.a<<endl;
    return output;
}

class Child : Base {
    private:
        int second;
    public:
        friend ostream & operator<<(ostream & output, const Child &n);

}

ostream & output<<(ostream & output, const Child &n) {
    output<<n.second<<Base:: ????<<endl;
    return output;
}

我的问题是，如何从子类中调用基类的友元函数输出其内容:

output<<n.second<<Base:: ????<<endl

提前致谢:)

Answer 1

output<<n.second<<static_cast<const Base&>(n)<<endl;