C ++重载运算符 - 减去两个相同类型的对象

Question

试着按照自学的C ++学习这本书。

到目前为止，我所创建的程序是一个具有Date对象的程序，它有四个参数。用户填写的三个参数是“月”，“日”和“年”。第四个参数是“旧”，即存储它的天数。为此，我编写了一个函数来计算它的天数，并将其设置为第四个参数。

这部分有效。它计算它的天数。

这本书要我减去两个Date类型的对象，找出它们之间的差异。为此，它特别要求我创建一个（ - ）的重载运算符，并减去这两个。这是我陷入困境的地方。我相信，我遇到问题的部分是用于访问它的调用。我继续得到“ambiguous overload for”operator-'的错误（操作数类型是'Date'和'Date'）。

它将两个对象都识别为Date。现在我需要一点帮助才能完成这一步。

我尝试在标题中使用了几个不同的东西，但也许我正在错误地实现它们。

-friend Date operator - (Date &ob1, Date &ob2);
-Date &operator-();
-Date &operator-(Date);
-Date operator-(Date);

如果你可以帮忙解决这个问题，那就太棒了。我是新人，而且我已经花了12个多小时来处理这个问题。

Main.cpp的

#include <iostream>
#include <time.h>
#include <ctime>
#include "Date.cpp" // Date class definition
using namespace std;

int main() {
    unsigned int birthMonth = 0;
    unsigned int birthDay = 0;
    unsigned int birthYear = 0;

    unsigned int dateToMonth = 0;
    unsigned int dateToDay = 0;
    unsigned int dateToYear = 0;

    cout << "Enter birth month (1-12): ";
    cin >> birthMonth;
    cout << "Enter birth day (1-31): ";
    cin >> birthDay;
    cout << "Enter birth year (1900 - 2000): ";
    cin >> birthYear;

    Date birthDate (birthMonth, birthDay, birthYear);
    Date tempDate (1, 1, 1, 1);

    cout << "To which date would you like to calculate to?\nEnter Day month (1-12): ";
    cin >> dateToMonth;
    cout << "Enter Day to calculate it to (1-31): ";
    cin >> dateToDay;
    cout << "Enter Year to calculate it to: ";
    cin >> dateToYear;

    Date dateTo (dateToMonth, dateToDay, dateToYear);

    pastDays(birthDate);
    pastDays(dateTo);

    cout << "\nHow many days ago is the birth date? " << birthDate.old << endl;
    cout << "How many days ago is the secondary date? " << dateTo.old << endl;

    // Here is where I get an error "ambiguous overload for "operator-' (operand types are 'Date' and 'Date')"
    cout << tempDate = birthDate - dateTo << endl;
    cout << tempDate.old;
}

Date.h

#ifndef DATE_H
#define DATE_H
#include <array>
#include <iostream>

class Date
  {
    friend std::ostream &operator<<( std::ostream &, const Date & );
public:
    Date( int m = 1, int d = 1, int y = 1900, int o = 0 ); // default constructor
    void setDate( int, int, int, int ); // set month, day, year
//    friend Date operator - (Date &ob1, Date &ob2);
    Date &operator-(); // Modified Line for Assignment
    Date &operator-(Date); // Modified Line for Assignment
//    Date operator-(Date);
    void pastDays (Date);
    static bool leapYear( int ); // is date in a leap year?
    unsigned int month;
    unsigned int day;
    unsigned int year;
    int old;
    static const std::array< unsigned int, 13 > days; // days per month
}; // end class Date

#endif

Date.cpp

#include <iostream>
#include <string>
#include "Date.h"
#include <time.h>
#include <ctime>
#include <conio.h>
#include "Date.h" // Date class definition
using namespace std;

   // initialize static member; one classwide copy
const array< unsigned int, 13 > Date::days = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

// Date constructor
Date::Date( int month, int day, int year, int old )
  {
    setDate( month, day, year, old );
  } // end Date constructor

// set month, day and year
void Date::setDate( int mm, int dd, int yy, int old )
  {
    if ( mm >= 1 && mm <= 12 )
        month = mm;
    else
        throw invalid_argument( "Month must be 1-12" );

    if ( yy >= 1900 && yy <= 2100 )
        year = yy;

    // test for a leap year
//        if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12){
//            if (dd >= 1 || dd <= 31)
//            day == dd;
//        }
//        if (month == 4 || month == 6 || month == 9 || month == 11){
//            if (dd >= 1 || dd <= 30)
//            day == dd;
//        }
//        if (month == 2)
//            if ( year % 4 != 0 ) {
//                if (dd >= 1 || dd <= 29)
//                day == dd;
//            }
//        if (month == 2)
//            if ( year % 4 != 0 ) {
//                if (dd >= 1 || dd <= 28)
//                day == dd;
//            }
//        else {
//            throw invalid_argument(
//                "Day is out of range for current month and year" );
//        }

    if ( ( month == 2 && leapYear( year ) && dd >= 1 && dd <= 29 ) ||
        ( dd >= 1 && dd <= days[ month ] ) )
        day = dd;
    else
        throw invalid_argument(
            "Day is out of range for current month and year" );


} // end function setDate

void pastDays (Date &entryDay) {
    //Creating Today date object
    time_t t = time(0);
    struct tm * now = localtime(&t);
    int currentYear = now -> tm_year + 1900;
    int currentMonth = now -> tm_mon + 1;
    int currentDay = now -> tm_mday;

    int birthMonth = entryDay.month;
    int birthDay = entryDay.day;
    int birthYear = entryDay.year;

    //The variable that will be assigned to the old parameter, which can then be subtracted from another time.
    int daysAgo = 0;
    entryDay.old = 0;

    cout << endl;
    cout << "First" << daysAgo << endl;
    cout << "BirthMonth: " << birthMonth << endl;
    cout << "BirthDay: " << birthDay << endl;
    cout << "BirthYear: " << birthYear << endl;

    //Lowering days to 1, to make transition between years easier.
//    while (birthDay > 1){
//        birthDay--;
//        daysAgo--;
//    }

    daysAgo = daysAgo - birthDay;
    daysAgo++;
    birthDay = 1;

    cout << endl;
    cout << "Second" << daysAgo << endl;
    cout << "BirthMonth: " << birthMonth << endl;
    cout << "BirthDay: " << birthDay << endl;
    cout << "BirthYear: " << birthYear << endl;

    //Lowering months to 1, to make transition between years easier.
    while (birthMonth > 1){
        if (birthMonth == 1 || birthMonth == 3 || birthMonth == 5 || birthMonth == 7 || birthMonth == 8 || birthMonth == 10 || birthMonth == 12){
            birthMonth--;
            daysAgo -= 31;
        }
        if (birthMonth == 4 || birthMonth == 6 || birthMonth == 9 || birthMonth == 11){
            birthMonth--;
            daysAgo -= 30;
        }
        if (birthMonth == 2)
            if ( currentYear % 400 == 0 ||
            ( currentYear % 100 != 0 && currentYear % 4 == 0 ) ) {
    birthMonth--;
    daysAgo -= 29;
            }
        else {
            birthMonth--;
            daysAgo -= 28;
        }
    }

    cout << endl;
    cout << "Third" << daysAgo << endl;
    cout << "BirthMonth: " << birthMonth << endl;
    cout << "BirthDay: " << birthDay << endl;
    cout << "BirthYear: " << birthYear << endl;

    //Incrementing year to current year
    while (birthYear < currentYear){
        if ( currentYear % 400 == 0 ||
        ( currentYear % 100 != 0 && currentYear % 4 == 0 ) ) {
            daysAgo = daysAgo + 366;
            birthYear++;
        }
        else {
            daysAgo = daysAgo + 365;
            birthYear++;
        }
    }

    cout << endl;
    cout << "Fourth" << daysAgo << endl;
    cout << "BirthMonth: " << birthMonth << endl;
    cout << "BirthDay: " << birthDay << endl;
    cout << "BirthYear: " << birthYear << endl;

    // Incrementing to current month
    while (birthMonth < currentMonth) {
        if (birthMonth == 1 || birthMonth == 3 || birthMonth == 5 || birthMonth == 7 || birthMonth == 8 || birthMonth == 10 || birthMonth == 12){
            birthMonth++;
            daysAgo += 31;
        }
        if (birthMonth == 4 || birthMonth == 6 || birthMonth == 9 || birthMonth == 11){
            birthMonth++;
            daysAgo += 30;
        }
        if (birthMonth == 2)
            if ( currentYear % 400 == 0 ||
            ( currentYear % 100 != 0 && currentYear % 4 == 0 ) ) {
    birthMonth++;
    daysAgo += 29;
            }
        else {
            birthMonth++;
            daysAgo += 28;
        }
    }

    cout << endl;
    cout << "Fifth" << daysAgo << endl;
    cout << "BirthMonth: " << birthMonth << endl;
    cout << "BirthDay: " << birthDay << endl;
    cout << "BirthYear: " << birthYear << endl;

    //Incrementing to current day, and adding the days to the daysAgo
    while (birthDay < currentDay){
        birthDay++;
        daysAgo++;
    }


    cout << endl;
    cout << "Sixth" << daysAgo << endl;
    cout << "BirthMonth: " << birthMonth << endl;
    cout << "BirthDay: " << birthDay << endl;
    cout << "BirthYear: " << birthYear << endl;

    //Assigning DaysAgo to input parameter.old
    entryDay.old = daysAgo;
}


    Date operator  - (Date &date1, Date &date2)
    {

    Date temp;
    temp.old   = date1.old   - date2.old;
    if(temp.old < 0)
    {
        temp.old = temp.old * -1;
    }
    return(temp);
    }

//Date operator-(Date birthDate)
////friend Distance operator - (Date &birthDate, Date &today)
//    {
////    int birthMonth = birthDate.month;
////    int birthDay = birthDate.day;
////    int birthYear = birthDate.year;
////    int birthOld = 0;
////    Date temp (birthDate.month, birthDate.day, birthDate.year, birthDate.old);
//
////    pastDays(today);
////    pastDays(birthDate);
//
////    int currentMonth = today.month;
////    int currentDay = today.day;
////    int currentYear = today.year;
//
////    int date1 = pastDays(today);
////    int date2 = pastDays(birthDate);
//    Date temp (birthDate.month, birthDate.day, birthDate.year);
//
////    int month, int day, int year, int old
////    temp.month = this -> month;
////    temp.month = this -> day;
////    temp.month = this -> year;
////    Date temp = *this;
//    cout << temp.old;
//
//    temp.old = *this -> old - birthDate.old;
//        //Here I get "Error: Invalid use of 'this' in non-member function;
//
//    return(temp);
//}

bool Date::leapYear( int testYear )
{
    if ( testYear % 400 == 0 ||
      ( testYear % 100 != 0 && testYear % 4 == 0 ) )
        return true; // a leap year
    else
        return false; // not a leap year
} // end function leapYear

// overloaded output operator
ostream &operator<<( ostream &output, const Date &d )
{
  static string monthName[ 13 ] = { "", "January", "February",
        "March", "April", "May", "June", "July", "August",
        "September", "October", "November", "December" };
  output << monthName[ d.month ] << ' ' << d.day << ", " << d.year;
  return output; // enables cascading
} // end function operator<<

Answer 1

使用复合赋值运算符（例如-=）定义二进制算术运算符（例如 - ）。您可能需要查看此binary arithmetic operator参考：

Date& operator-=(const X& rhs) {                           
  /* subtraction of rhs to *this takes place here */
  this->year - rhs.year; // This is the easy one

  /* Here you will have to play around with this->month and this->day */

  return *this; // return the result by reference
}


friend Date operator-(Date lhs, const Date& rhs) {
  lhs -= rhs; // use compound assignment
  return lhs; // return the result by value
}

Answer 2

的main.cpp

#include <iostream>
#include <time.h>
#include <ctime>
#include "Date.cpp" // Date class definition
using namespace std;

int main() {
    unsigned int birthMonth = 0;
    unsigned int birthDay = 0;
    unsigned int birthYear = 0;

    unsigned int dateToMonth = 0;
    unsigned int dateToDay = 0;
    unsigned int dateToYear = 0;

    cout << "Enter birth month (1-12): ";
    cin >> birthMonth;
    cout << "Enter birth day (1-31): ";
    cin >> birthDay;
    cout << "Enter birth year (1900 - 2000): ";
    cin >> birthYear;

    Date birthDate (birthMonth, birthDay, birthYear);
    Date tempDate (1, 1, 1, 1);

    cout << "To which date would you like to calculate to?\nEnter Day month (1-12): ";
    cin >> dateToMonth;
    cout << "Enter Day to calculate it to (1-31): ";
    cin >> dateToDay;
    cout << "Enter Year to calculate it to: ";
    cin >> dateToYear;

    Date dateTo (dateToMonth, dateToDay, dateToYear);

    pastDays(birthDate);
    pastDays(dateTo);

    cout << "\nHow many days ago is the birth date? " << birthDate.old << endl;
    cout << "How many days ago is the secondary date? " << dateTo.old << endl;

    tempDate = birthDate - dateTo;
    cout << tempDate.old;
}

Date.h

#ifndef DATE_H
#define DATE_H
#include <array>
#include <iostream>

class Date
  {
    friend std::ostream &operator<<( std::ostream &, const Date & );
//  friend Date operator-(Date, Date);
public:
    Date( int m = 1, int d = 1, int y = 1900, int o = 0 ); // default constructor
    void setDate( int, int, int, int ); // set month, day, year
//  friend Date operator-(Date, Date);
    Date operator-(); // Modified Line for Assignment
    Date operator-(Date); // Modified Line for Assignment
//    Date operator-(Date);
    void pastDays (Date);
    static bool leapYear( int ); // is date in a leap year?
    unsigned int month;
    unsigned int day;
    unsigned int year;
    int old;
    static const std::array< unsigned int, 13 > days; // days per month
}; // end class Date

#endif

Date.cpp

#include <iostream>
#include <string>
#include "Date.h"
#include <time.h>
#include <ctime>
#include <conio.h>
#include "Date.h" // Date class definition
using namespace std;

   // initialize static member; one classwide copy
const array< unsigned int, 13 > Date::days = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

// Date constructor
Date::Date( int month, int day, int year, int old )
  {
    setDate( month, day, year, old );
  } // end Date constructor

// set month, day and year
void Date::setDate( int mm, int dd, int yy, int old )
  {
    if ( mm >= 1 && mm <= 12 )
        month = mm;
    else
        throw invalid_argument( "Month must be 1-12" );

    if ( yy >= 1900 && yy <= 2100 )
        year = yy;

    if ( ( month == 2 && leapYear( year ) && dd >= 1 && dd <= 29 ) ||
        ( dd >= 1 && dd <= days[ month ] ) )
        day = dd;
    else
        throw invalid_argument(
            "Day is out of range for current month and year" );


} // end function setDate

void pastDays (Date &entryDay) {
    //Creating Today date object
    time_t t = time(0);
    struct tm * now = localtime(&t);
    int currentYear = now -> tm_year + 1900;
    int currentMonth = now -> tm_mon + 1;
    int currentDay = now -> tm_mday;

    int birthMonth = entryDay.month;
    int birthDay = entryDay.day;
    int birthYear = entryDay.year;

    //The variable that will be assigned to the old parameter, which can then be subtracted from another time.
    int daysAgo = 0;
    entryDay.old = 0;

    cout << endl;
    cout << "First" << daysAgo << endl;
    cout << "BirthMonth: " << birthMonth << endl;
    cout << "BirthDay: " << birthDay << endl;
    cout << "BirthYear: " << birthYear << endl;

    //Lowering days to 1, to make transition between years easier.
//    while (birthDay > 1){
//        birthDay--;
//        daysAgo--;
//    }

    daysAgo = daysAgo - birthDay;
    daysAgo++;
    birthDay = 1;

    cout << endl;
    cout << "Second" << daysAgo << endl;
    cout << "BirthMonth: " << birthMonth << endl;
    cout << "BirthDay: " << birthDay << endl;
    cout << "BirthYear: " << birthYear << endl;

    //Lowering months to 1, to make transition between years easier.
    while (birthMonth > 1){
        if (birthMonth == 1 || birthMonth == 3 || birthMonth == 5 || birthMonth == 7 || birthMonth == 8 || birthMonth == 10 || birthMonth == 12){
            birthMonth--;
            daysAgo -= 31;
        }
        if (birthMonth == 4 || birthMonth == 6 || birthMonth == 9 || birthMonth == 11){
            birthMonth--;
            daysAgo -= 30;
        }
        if (birthMonth == 2)
            if ( currentYear % 400 == 0 ||
            ( currentYear % 100 != 0 && currentYear % 4 == 0 ) ) {
    birthMonth--;
    daysAgo -= 29;
            }
        else {
            birthMonth--;
            daysAgo -= 28;
        }
    }

    cout << endl;
    cout << "Third" << daysAgo << endl;
    cout << "BirthMonth: " << birthMonth << endl;
    cout << "BirthDay: " << birthDay << endl;
    cout << "BirthYear: " << birthYear << endl;

    //Incrementing year to current year
    while (birthYear < currentYear){
        if ( currentYear % 400 == 0 ||
        ( currentYear % 100 != 0 && currentYear % 4 == 0 ) ) {
            daysAgo = daysAgo + 366;
            birthYear++;
        }
        else {
            daysAgo = daysAgo + 365;
            birthYear++;
        }
    }

    cout << endl;
    cout << "Fourth" << daysAgo << endl;
    cout << "BirthMonth: " << birthMonth << endl;
    cout << "BirthDay: " << birthDay << endl;
    cout << "BirthYear: " << birthYear << endl;

    // Incrementing to current month
    while (birthMonth < currentMonth) {
        if (birthMonth == 1 || birthMonth == 3 || birthMonth == 5 || birthMonth == 7 || birthMonth == 8 || birthMonth == 10 || birthMonth == 12){
            birthMonth++;
            daysAgo += 31;
        }
        if (birthMonth == 4 || birthMonth == 6 || birthMonth == 9 || birthMonth == 11){
            birthMonth++;
            daysAgo += 30;
        }
        if (birthMonth == 2)
            if ( currentYear % 400 == 0 ||
            ( currentYear % 100 != 0 && currentYear % 4 == 0 ) ) {
    birthMonth++;
    daysAgo += 29;
            }
        else {
            birthMonth++;
            daysAgo += 28;
        }
    }

    cout << endl;
    cout << "Fifth" << daysAgo << endl;
    cout << "BirthMonth: " << birthMonth << endl;
    cout << "BirthDay: " << birthDay << endl;
    cout << "BirthYear: " << birthYear << endl;

    //Incrementing to current day, and adding the days to the daysAgo
    while (birthDay < currentDay){
        birthDay++;
        daysAgo++;
    }


    cout << endl;
    cout << "Sixth" << daysAgo << endl;
    cout << "BirthMonth: " << birthMonth << endl;
    cout << "BirthDay: " << birthDay << endl;
    cout << "BirthYear: " << birthYear << endl;

    //Assigning DaysAgo to input parameter.old
    entryDay.old = daysAgo;
}

bool Date::leapYear( int testYear )
{
    if ( testYear % 400 == 0 ||
      ( testYear % 100 != 0 && testYear % 4 == 0 ) )
        return true; // a leap year
    else
        return false; // not a leap year
} // end function leapYear

// overloaded output operator
ostream &operator<<( ostream &output, const Date &d )
{
  static string monthName[ 13 ] = { "", "January", "February",
        "March", "April", "May", "June", "July", "August",
        "September", "October", "November", "December" };
  output << monthName[ d.month ] << ' ' << d.day << ", " << d.year;
  return output; // enables cascading
} // end function operator<<

Date Date::operator-(Date rhs) {
  //lhs -= rhs; // use compound assignment
  //return lhs; // return the result by value
  Date n = *this;
  n.old -= rhs.old;
  return n;
}