c++ - 创建比较两个对象的方法

Question

编辑!!

我正在自学 C++，并且只学习类。为了练习，我创建了一个 Date类的一些方法。我目前正在尝试练习这个问题:

Use the Date class to create a method that compares two Date objects and returns the larger of the two.

所以我已经在下面制作了一些代码和方法。这是我感到困惑的地方:当你调用一个方法时，它的形式是:<object>.<method> .假设我有两个 Date 对象 date1和 date2 .我不明白如何创建一个采用两个日期对象的日期方法，因为该方法已经作用于其中一个对象。换句话说，我希望有这样的东西:date1.compareDate(date2)并且此方法会返回具有更大值的对象。有人可以解释一下我是如何解决这个问题的吗？

我试图在我的方法中这样做:compareDate()。我做了另一种方法转换，它创建了一个 YYYYMMDD 形式的整数，我可以只使用简单的 bool 逻辑来比较更大的值。

请注意我要退回较大的 Date对象而不是 bool 值。

提前谢谢你。

#include <iostream>
#include <iomanip>
using namespace std;

// Class declaration statement
class Date
{
    private:
        int month;
        int day;
        int year;
    public:

        Date(int = 7, int = 4, int = 2012); // Constructor
        void setDate(int, int, int);        // Member to copy a date
        void showDate();                    // Member method to display date
        int convert();
        bool leapYear();
        string dayOfWeek();
        void nextDay();
        void priorDay();
        Date compareDate(Date, Date);
};

// Class Implementation section
Date::Date(int mm, int dd, int yyyy)
{
    month = mm;
    day = dd;
    year = yyyy;
}

void Date::setDate(int mm, int dd, int yyyy)
{
    month = mm;
    day = dd;
    year = yyyy;
}

void Date::showDate()
{
    cout << "The date is ";
    cout << setfill('0')
         << setw(2) << month << '/'
         << setw(2) << day << '/'
         << setw(2) << year % 100;
    cout << endl;
}

int Date::convert()
{
    // Convert date to the integer format:  YYYYMMDD
    return year*10000 + month*100 + day;
}

bool Date::leapYear()
{
    if( (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0) )
        return true;
    else
        return false;
}

string Date::dayOfWeek()
{
    int dayInt;
    int mm, yyyy, dd, YYYY;
    int century, T, dayOfWeek;


    yyyy = year;
    mm = month;
    dd = day;

    if( mm < 3 )
    {
        mm = mm + 12;
        yyyy = yyyy - 1;
    }        

    century = int( yyyy/100 );
    YYYY = yyyy%100;

    T = dd + int( 26 * (mm + 1)/10) + YYYY + int(YYYY/4) + int( century/4)
        -2*century;

    dayOfWeek = T % 7;

    if( dayOfWeek < 0 )
        dayOfWeek += 7;

    if( dayOfWeek == 0 )
        return "Saturday";
    else if( dayOfWeek == 1)
        return "Sunday";
    else if( dayOfWeek == 2)
        return "Monday";
    else if( dayOfWeek == 3)
        return "Tuesday";
    else if( dayOfWeek == 4)
        return "Wednesday";
    else if( dayOfWeek == 5)
        return "Thursday";
    else if( dayOfWeek == 6)
        return "Friday";
    else
    {
        cout << "dayOfWeek = " << dayOfWeek << endl;
        return "Bad dayOfWeek Calc";
    }
}

void Date::nextDay()
{
    // Increment month and day if at 31 days in month
    // Skip December because have to increment year too
    if( (month == 1 || month == 3  || month == 5 || month == 7 || 
         month == 8 || month == 10) && day == 31 )
    {
        month++;
        day = 1;
    }
    // Increment month and day if at 30 days in month
    else if( (month == 4 || month == 6  || month == 9 || month == 11)
                && day == 30)
    {
        month++;
        day = 1;
    }
    // New year
    else if( month == 12 && day == 31 )
    {
        month = 1;
        day = 1;
        year++;
    }
    // Leap year
    else if( leapYear() && month == 2 && day == 29 )
    {
        month = 3;
        day = 1;
    }
    // Not leap year
    else if( !leapYear() && month == 2 && day == 28)
    {
        month = 3;
        day = 1;
    }
    // Regular day
    else
        day++;
}

void Date::priorDay()
{
    // Increment month and day if at 31 days in month
    // Skip December because have to increment year too
    if( (month == 5 || month == 7 || 
         month == 8 || month == 10 || month == 12) && day == 1 )
    {
        month--;
        day = 30;
    }
    // Increment month and day if at 30 days in month
    else if( (month == 2 || month == 4 || month == 6  || month == 9 || month == 11)
                && day == 1)
    {
        month--;
        day = 31;
    }
    // beginning year
    else if( month == 1 && day == 1 )
    {
        month = 12;
        day = 31;
        year--;
    }
    // Leap year
    else if( leapYear() && month == 3 && day == 1 )
    {
        month--;
        day = 29;
    }
    // Not leap year
    else if( !leapYear() && month == 3 && day == 1)
    {
        month--;
        day = 28;
    }
    // Regular day
    else
        day--;

}

Date Date::compareDate(Date date1, Date date2)
{
   // Return the greater date
    if( date1.convert() > date2.convert() )
        return date1;
    else
        return date2;
}


int main()
{
    Date c(4,1,2000);
    Date d(11, 1, 2013);
    b.setDate(12,25,2009);    

    cout << Date.compareDate(c,d) << endl;

    return 0;
}

Answer 1

您可以使用运算符(您应该自己编写)比较您的 Date 对象

friend bool operator> (const Date& D1, const Date& D2)
{
  return D1.convert() > D2.convert();
}

当且仅当 D1 > D2 时，此运算符应该返回 true。如果此运算符需要访问 Date 对象的私有(private)部分，则必须在 Date 类中将其声明为 friend。