Comparing Function

#include <functional>
#include <iomanip>
#include <iostream>
#include <string>
#include <list>

struct Student
{
    friend std::istream& operator >>(std::istream& input, Student& stu)
    {
        return input >> stu.number >> stu.name >> stu.chinese_score >> stu.math_score >> stu.english_score;
    }

    friend std::ostream& operator <<(std::ostream& output, const Student& stu)
    {
        output << std::setw(15) << stu.number
               << std::setw(15) << stu.name
               << std::setw(5)  << stu.chinese_score
               << std::setw(5)  << stu.math_score
               << std::setw(5)  << stu.english_score;
        return output;
    }

    std::string number;
    std::string name;
    int chinese_score;
    int math_score;
    int english_score;
};

template <typename T, typename Fn = std::less<T> >
struct Compare: std::binary_function<Student, Student, bool>
{
    Compare(const T Student::*_p, Fn _fn=Fn()): p(_p), fn(_fn) {}
    bool operator ()(const Student& a, const Student& b) const
    {
        return fn(a.*p, b.*p);
    }

private:
    const T Student::*p;
    Fn fn;
};

int main()
{
    std::list<Student> student_list;
    student_list.sort(Compare<std::string>(&Student::number));  //std::less<std::string>
    student_list.sort(Compare<int, std::greater<int> >(&Student::chinese_score));
}