has-a关系——多重私有继承

#ifndef _STUDENT_H_
#define _STUDENT_H_

#include <iostream>
#include <string>
#include <valarray>

class Student : private std::string, private std::valarray<double>
{
private:
    typedef std::valarray<double> ArrayDb;

    //private method for scores output
    std::ostream & arr_out(std::ostream & os) const;

public:
    Student()                                           : std::string("Null Student"),  ArrayDb()       {}
    explicit Student(const std::string & s)             : std::string(s),               ArrayDb()       {}
    explicit Student(int n)                             : std::string("Nully"),         ArrayDb(n)      {}
    Student(const std::string & s, int n)               : std::string(s),               ArrayDb(n)      {}
    Student(const std::string & s, const ArrayDb & a)   : std::string(s),               ArrayDb(a)      {}
    Student(const char * str, const double * pd, int n) : std::string(str),             ArrayDb(pd, n)  {}
    ~Student() {}

    double Average(void) const;
    const std::string & Name(void) const;
    //double & operator[](int i);
    //const double & operator[](int i) const;
    using std::valarray<double>::operator[];    //使用using重新定义基类方法在私有继承中的访问权限

    //friends
    //inout
    friend std::istream & operator>>(std::istream & is, Student & stu); //1 word
    friend std::istream & getline(std::istream & is, Student & stu);    //1 line
    //output
    friend std::ostream & operator<<(std::ostream & os, const Student & stu);
};

#endif

#include "student.h"
using std::ostream;
using std::istream;
using std::endl;
using std::string;

//public methods
double Student::Average(void) const
{
    if(ArrayDb::size() > 0)
    {
        return ArrayDb::sum() / ArrayDb::size();
    }
    else
    {
        return 0;
    }
}

const string & Student::Name(void) const
{
    return (const string &)*this;
}
/*
double & Student::operator[](int i)
{
    return ArrayDb::operator[](i);
}

const double & Student::operator[](int i) const
{
    return ArrayDb::operator[](i);
}
*/
//private method
ostream & Student::arr_out(ostream & os) const
{
    int i;
    if(ArrayDb::size() > 0)
    {
        for(i = 0; i < ArrayDb::size(); i++)
        {
            //os << ArrayDb::operator[](i) << " ";
            os << ((const ArrayDb &)*this)[i] << " ";
            if(i % 5 == 4)
            {
                os << endl;
            }
        }
        if(i % 5 != 0)
        {
            os << endl;
        }
    }
    else
    {
        os << "empty array";
    }
    return os;
}

//friend methods
istream & operator>>(istream & is, Student & stu)
{
    is >> (string &)stu;
    return is;
}

istream & getline(istream & is, Student & stu)
{
    getline(is, (string &)stu);
    return is;
}

ostream & operator<<(ostream & os, const Student & stu)
{
    os << "Scores for " << (const string &)stu << ":\n";
    stu.arr_out(os);
    return os;
}

#include <iostream>
#include "student.h"
using std::cin;
using std::cout;
using std::endl;

void set(Student & sa, int n)
{
    cout << "Please enter the student's name: ";
    getline(cin, sa);
    cout << "Please enter " << n << " quiz scores:\n";
    for(int i = 0; i < n; i++)
    {
        cin >> sa[i];
    }
    while(cin.get() != '\n')
    {
        continue;
    }
}

const int pupils = 3;
const int quizzes = 5;

int main(void)
{
    Student ada[pupils] = {Student(quizzes), Student(quizzes), Student(quizzes)};

    for(int i = 0; i < pupils; i++)
    {
        set(ada[i], quizzes);
    }
    cout << "\nStudent List:\n";
    for(int i = 0; i < pupils; i++)
    {
        cout << ada[i].Name() << endl;
    }
    cout << "\nResults:";
    for(int i = 0; i < pupils; i++)
    {
        cout << endl << ada[i];
        cout << "average: " << ada[i].Average() << endl;
    }
    cout << "Done.\n";

    return 0;
}