C++。用类模板实现2个数相加。error C2679: binary '<<' : no opera~~~

Question

error C2679: binary '<<' : no operator defined which takes a right-hand operand of type 'class jf<int>' (or there is no acceptable conversion)
执行 cl.exe 时出错.

#include<iostream>
using namespace std;
template <class numtype>
class jf
{private:
numtype x,y;
public:
jf(numtype a,numtype b):x(a),y(b){}
jf<numtype> plus();
};
template <class numtype>
jf<numtype> jf<numtype>::plus()
{return(x+y);}
int main()
{jf<int> j1(3,4);
cout<<"x+y="<<j1.plus();
return 0;
}

Answer 1

改成numtype plus();

追问

为什么要这样改呢？不太懂。

追答

jf类的plus方法不是要返回x+y吗，类型是numtype