模板类的友元重载

模板类的友元重载，注意

#include <iostream>

using namespace std;

template <class T>
class Test;                        // 模板类前置声明

template<class T>

ostream& operator << (ostream& out, const Test<T>& obj);      // 模板类友元前置声明

template<class T>

class Test
{

public:

	friend ostream& operator << <> (ostream& out, const Test<T>& obj);       // 模板类友元定义，注意格式"<>"

	Test(T n=0):num(n){}

	Test(const Test<T>& copy)
	{

		num = copy.num;

	}

private:

	T num;

};

template<class T>

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

	out<<obj.num<<endl;

	return out;
}

int main()
{

	Test<int> t(2);

	cout<<t;

	return 0;
}

// 第二种格式
/*

#include <iostream>

using namespace std;

template<class T>

class Test

{

public:

    template<class S>                   // 注意<class S>S
    friend ostream& operator << (ostream& out, const Test<S>& obj);


    Test(T n=0):num(n) {}



    Test(const Test<T>& copy)

    {

        num = copy.num;

    }



private:

    T num;

};
// 注意<class T>和<class S>都行

template<class T>


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


        out<<obj.num<<endl;


        return out;
}


int main()


{


    Test<int> t(2);


    cout<<t;


    return 0;


}