class Complex
{
public:
    friend ostream& operator<<(ostream& out,Complex& c);
}

//类外
ostream& operator<<(ostream& out,Complex<T>& c)
{
    out<<c.a<<" "<<c.b<<endl;
    return out;
}
这样写报错 模板类中友元函数重载<<运算符 应该怎么写？