函数对象plus的问题

[ws_yqr]

class Two_num
{
friend istream&
operator>>(istream& in, Two_num& loc);
friend ostream&
operator<<(ostream& out, const Two_num&loc);
public:
Two_num():first(0), second(0){}
private:
int first;
int second;
};

int main()
{
plus<Two_num> Add;
Two_num i1, i2;
cin >> i1 >> i2;
// Two_num i3 = Add(i1, i2);
cout << i3 << endl;
}
//处为什么有错误

[pengzhixi]

这个函数对象的定义是怎么样的呢?

[hz_yck]

估计要自己重载+吧

[zgjxwl]

operator +或者Add函数是怎么实现的。。