目前我正在编写一个程序，该程序有一个部分来确定两个日期之间的天数差异，但通过重载减号运算符。

我目前正在盯着我的屏幕绘制一个完全空白。我脑子里有一些转瞬即逝的想法，但它们确实是转瞬即逝的。

总的来说.cpp将有两个变量，例如beethovenDeathDate和beethovenBirthDate，将被减去以确定他活了多长时间。如果我没记错的话，大约是 22000 天。

所以事不宜迟，这是我的代码：

日期.cpp

const std::string Date::MONTH_STRINGS[] = 
{
    "", //one based indexing
    "January",
    "February",
    "March",
    "April",
    "May", 
    "June",
    "July",
    "August",
    "September",
    "October",
    "November",
    "December"
};
const int Date::DAYS_PER_MONTH[] =
{
    0, //one based indexing
    31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};      
Date::Date(int day, int month, int year) : _year(year), _month(month), _day(day)
{
    isValid();
}
Date::Date()
{
    time_t t = time(0);   // get time now
    struct tm * now = localtime( & t );
    _year = now -> tm_year + 1900;
    _month = now -> tm_mon + 1;
    _day = now -> tm_mday;
}
int Date::maxDay(int month, int year)
{
    int ret = DAYS_PER_MONTH[month];
    if(isLeapYear(year) == true && month == 2)
    {
        ++ret;
    }
    return ret;
}
void Date::addDay(bool forward)
{
    if(forward)
    {
        if(_day < maxDay(_month, _year))
        {
            ++_day;
        }
        else
        {
            _day = MIN_DAY;
            ++_month;
            if(_month > MAX_MONTH)
            {
                _month = MIN_MONTH;
                ++_year;
            }    
        }
    }
    else
    {
        if(_day <= MIN_DAY)
        {
            --_month;
            if(_month < MIN_MONTH)
            {
                _month = MAX_MONTH;
                --_year;
            } 
            _day = maxDay(_month, _year);
        }
        else
        {
            --_day;
        }
    }    
}

std::string Date::toString() const
{
    if(isValid() == false)
    {
        return std::string();
    }
    std::stringstream ss;
    ss  << MONTH_STRINGS[_month] << " " << _day << ", " <<  _year;
    return ss.str();            
}    

bool Date::isValid() const
{
    if(_month < MIN_MONTH || _month > MAX_MONTH)
    {
        std::cerr << "Invalid date " << std::endl;
        return false;
    }
    int daysThisMonth = maxDay(_month, _year);
    if(_day < MIN_DAY || _day > daysThisMonth)
    {
        std::cerr << "Invalid date " << std::endl;            
        return false;   
    }
    return true;
}
bool Date::isLeapYear(int year)
{
    if(!(year % 4))
    {
        if(!(year % 100))
        {
            if(!(year % 400))
            {
                return true;
            }
            else
            {
                return false;
            }
        }
        else
        {
            return true;
        }
    }
    else
    {
        return false;
    }
}
bool Date::isLeapYear() const
{
    return isLeapYear(_year);
}
bool Date::isLeapDay() const
{
    return isLeapDay(_day, _month, _year);
}
bool Date::isLeapDay(int day, int month, int year) 
{
    if(day == 29 &&  month == 2 && isLeapYear(year) == true)
    {
        return true;
    }
    else
    {
        return false;
    }
}

void Date::addYears(int years)
{
    if(years == 0)
    {
        return;
    }
    if(isLeapDay() && !isLeapDay(_day, _month, _year + years))
    {
        _day = Date::DAYS_PER_MONTH[_month];
    }
    _year += years;
}
void Date::addMonths(int months)    
{
    if(months == 0)
    {
        return;
    }
    int deltayears = months / MAX_MONTH;
    int deltamonths = months % MAX_MONTH;
    int newMonth = 0;
    if(months > 0)
    {
        newMonth = (_month + deltamonths) % MAX_MONTH;
        if((_month + deltamonths) > MAX_MONTH)
        {
            ++deltayears;
        }
    }
    else
    {
        if((_month + deltamonths) < MIN_MONTH)
        {
            --deltayears;
            newMonth = _month + deltamonths + MAX_MONTH;
        }
        else
        {
            newMonth = _month + deltamonths;
        }       
    }
    if(_day > maxDay(newMonth, _year + deltayears))
    {
        _day = maxDay(newMonth, _year + deltayears);
    }
    _year += deltayears;
    _month = newMonth;
}
void Date::addDays(int days)
{
    if(days == 0)
    {
        return;
    }
    if(days < 0)
    {
        for(int i = 0; i > days; --i)
        {
            addDay(false);
        }
        return;
    }
    for(int i = 0; i < days; ++i)
    {
        addDay(true);
    }
}
std::ostream& operator<<(std::ostream& os, const Date& date)
{
    os << date.toString();
    return os;
}
Date Date::operator+(int days) const
{
    Date ret = *this;
    ret.addDays(days);
    return ret;
}
Date& Date::operator+=(int days)
{
    addDays(days);
    return *this;
}
//This is where I get stumped (the parameters was just one of my failed experiments
Date& Date::operator-(int day, int month, int year)
{
}