#ifndef _MYSMART_PTR_H
#define _MYSMART_PTR_H    // 1.在template class定義前先宣告
template 
class mysmart_ptr;    // 2.friend function在template class定義前也要先宣告
template 
std::ostream& operator <<(std::ostream &os, const mysmart_ptr &rhs);    template 
class mysmart_ptr
{
public:
    //same stuff here blah blah blah
    //except change operator << to this
    //note the '<>' that's important!
    // 3. 重點!!!要多加一個'<>'      friend std::ostream& operator << <>(std::ostream &os, const mysmart_ptr &rhs);        // 下面是宣告正確,但complie時過不了的code
    //friend std::ostream& operator << (std::ostream &os, const mysmart_ptr &rhs);     private:
    ...
};
#include "mysmart_ptr.cpp"
#endif