C++ 友元运算符重载 cin>>

Question

我正在用友元运算符替换读入函数。我在 void 函数中引用友元运算符时遇到问题。我在 void GetDates 函数中收到错误 "No member named 'Read' in Date"。有谁知道如何解决这一问题？谢谢！

问题二：我现在正在使用 cout<< 运算符，但我的变量收到错误消息：“'mn' 是 'Date' 的私有成员”

class Date {
private:
    int mn;        //month component of a date
    int dy;        //day component of a date
    int yr;        //year comonent of a date

public:
    //constructors
    Date() : mn(0), dy(0), yr(0)
    {}
    Date(int m, int d, int y) : mn(m), dy(d), yr(y)
    {}

    //input/output functions
    friend istream& operator>>(istream& Read, Date& d);   //overload friend Read
    friend ostream& operator<<(istream& write, Date& d);   //overload friend write                                  
    void GetDates();
    void Sort();
};

//Date class member functions

istream& operator >>(istream& Read, Date& d) //**NEED TO REPLACE with overload vs as friends to Date function**
{
    char skip_char;

    Read >> d.mn >> skip_char >> d.dy >> skip_char >> d.yr;
    return Read;
}


void GetDates(Date l[], int &n)      //reads list l, and returns count in n
   {

       cout << "How many date values are to be processed (1 - 100)? ";
       cin >> n;

       while ((n < 0) || (n > 100)) {
           cout << "Invalid value; enter number between 0 and 100: ";
           cin >> n;
       }

       for (int i = 0; i < n; i++) {
           cout << "Enter a date (mm/dd/yyyy): ";
           l[i].Read(); //ERROR HERE
       }
   }



ostream& operator <<(ostream& write, Date& d) //friend write
{
    if (d.mn < 10)
        cout << '0';
    cout << d.mn << '/';
    if (d.dy < 10)
        cout << '0';
    cout << d.dy << '/';
    if (d.yr < 1000)
        cout << '0';
    if (d.yr < 100)
        cout << '0';
    if (d.yr < 10)
        cout << '0';
    cout << d.yr;
    return write;
}

Answer 1

Read 是您要从中提取的 stream 的名称。您可以读取的流示例是 cin。您需要替换此行：

l[i].Read(); //ERROR HERE

和

cin >> l[i];

在 operator>> 中，cin 对象现在称为 Read。

您的 operator<< 的问题是它需要声明为 friend，就像您对 operator>> 所做的那样。

此外，您正在写入 cout 而不是写入 write。一旦您尝试写入任何其他流，这将不起作用。

C++ 友元运算符重载 cin>>

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