模板类的友元重载，用C++代码实现

#include <iostream>

using namespace  std;

template<class T>

class Test;

template<class T>

ostream& operator << (ostream& out, const Test<T> &obj);

template <class T>

class Test

{
private:
int num;
public:
Test(int n=0){num=n;}

friend ostream& operator<< <> (ostream& out, const Test<T>&obj);
//注意在<<后加上<>表明这是个函数模板

};

template <class T>

ostream& operator<< (ostream& out , const Test<T>&obj)

{
cout << obj.num;
return out;

}

int main()

{
Test<int> t(2);
cout << t;
return 0;

}