Date类(C++ Programming Language第10章课后题10.6.2的一部分)

//Data.h

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

class Date
{
public:
 enum Month { jan = 1, feb, mar, apr, may, jun,
  jul, aug, sep, oct, nov, dec };
 class BadDate{ };
 Date(int dd = 0, Month mm = Month(0), int yy = 0);
 int day( ) const;
 Month month( ) const;
 int year( ) const;
 //string string_rep( ) const;
 //void char_rep(char s[]) const;
 void print_date( );
 //使用Date之前应调用set_default函数设置缺省日期
 static void set_default(int, Month, int);

 Date& add_year(int n);
 Date& add_month(int n);
 Date& add_day(int n);
private:
 int d;
 Month m;
 int y;
 static Date default_date;
 int get_days(Month mm);
};

int leapyear(int yy); 

//Date.cpp

#include "Date.h"

Date::Date(int dd, Month mm, int yy)
{
    if(yy == 0)
  y = default_date.year( );
 if(mm == Month(0))
  m = default_date.month( );
 if(dd == 0)
  d = default_date.day( );
 int max;
 switch(mm)
 {
 case feb:
  max = 28 + leapyear(yy);
  break;
 case apr:
 case jun:
 case sep:
 case nov:
  max = 30;
  break;
 case jan:
 case mar:
 case may:
 case jul:
 case aug:
 case oct:
 case dec:
  max = 31;
  break;
 default:
  throw BadDate( );
 }

 if(dd < 1 || dd > max)
  throw BadDate( );
 y = yy;
 m = mm;
 d = dd;
}

int Date::day( ) const
{
 return d;
}

enum Date::Month Date::month( ) const
{
 return m;
}

int Date::year( ) const
{
 return y;
}

void Date::set_default(int d, Month m, int y)
{ 
 default_date = Date(d, m, y);
}

Date& Date::add_year(int n)
{
 if(n != 0)
 {
  if( d == 29 && m == feb && !leapyear(y + n) )
  {
   d = 28;
  }
  y = y + n;
 }
 return *this;
}
Date& Date::add_month(int n)
{
 if(n == 0)
  return *this;
 if(n > 0)
 {
  int delta_y = n/12;
  int mm = m + n%12;
  if(mm > 12)
  {
   delta_y++;
   mm -= 12;
  }
  y += delta_y;
  if(mm == 2 && d >28)
  {
   if( leapyear(y) )
    d = 29;
   else
    d = 28;
  }
  if(d == 31)
  {
   if( (mm == apr) || (mm == jun) ||
    (mm == sep) || (mm == nov) )
   {
    d = 30;
   }
  }
  m = Month(mm);
  return *this;
 }
 if(n < 0)
 {
  n = -n;
  int delta_y = n/12;
  int mm = m - n%12;
  if(mm <= 0)
  {
   delta_y++;
   mm += 12;
  }
  y -= delta_y;
  if(mm == 2 && d >28)
  {
   if( leapyear(y) )
    d = 29;
   else
    d = 28;
  }
  if(d == 31)
  {
   if( (mm == apr) || (mm == jun) ||
    (mm == sep) || (mm == nov) )
   {
    d = 30;
   }
  }
  m = Month(mm);
  return *this;
 }
 return *this;
}
Date& Date::add_day(int n)
{
 if( n == 0 )
  return *this;
 if( n > 0 )
 {
  //计算本月剩余天数
  int totalDays = get_days(m);
  int daysLeft = totalDays - d;
  if(n <= daysLeft)
  {
   d = d + n;
  }
  else if(n > daysLeft)
  {
   //把日期调整到下个月1号
   n = n - (daysLeft + 1);
   add_month(1);
   d = 1;
   //模拟时间按月的流逝，最后得到正确的日期
   int daysInMonth = get_days(m);
   while( n >= daysInMonth )
   {
    add_month(1);
    n = n - daysInMonth;
    daysInMonth = get_days(m);
   }
   d = d + n;
  }
 }
 else if( n < 0 )
 {
  //把n变为正值
  n = -n;
  //计算本月剩余天数
  int totalDays = get_days(m);
  int daysLeft = totalDays - d;
  //把时间调整到本月的最后一天
  n = n + daysLeft;
  d = d + daysLeft;
  //模拟时间按月的倒流，最后得到正确的日期
  int daysInMonth = get_days(m);
  while( n >= daysInMonth )
  {
   add_month(-1);
   n = n - daysInMonth;
   daysInMonth = get_days(m);
  }
  d = d - n;
 }
 return *this;
}

int Date::get_days(Month mm)
{
 int days;
 if(mm == 0)
  return 0;
 switch(mm)
 {
 case jan:
 case mar:
 case may:
 case jul:
 case aug:
 case oct:
 case dec:
  days = 31;
  break;
 case apr:
 case jun:
 case sep:
 case nov:
  days = 30;
  break;
 case feb:
  days = 28 + leapyear(y);
 }
 return days;
}

void Date::print_date( )
{
 cout<<y<<'-'<<m<<'-'<<d<<endl;
}

int leapyear(int yy)
{
 int iRet = 0;
 if( (yy % 4 == 0) && (yy % 100 != 0) )
  iRet = 1;
 if( yy % 400 == 0 )
  iRet = 1;
 return iRet;
}
Date Date::default_date(3, feb, 1981);

int main( )
{
 //Date::set_default();
 Date testDate(29, Date::Month::feb, 2000);
 testDate.print_date( );
 cout<<"after add -1 years:";
 testDate.add_year(-1);
 testDate.print_date( );
 system("pause");
 return 0;
}