Listing 1  Date类的成员定义
// date.h: A simple date class

struct Date
{
   int month;
   int day;
   int year;
   
   Date * interval(const Date&);
};

/* End of File */

Listing 2   Date::interval()的实现
//date.cpp: Implement the Date class

#include "date.h"

inline int isleap(int y)
  {return y%4 == 0 && y%100 != 0 || y%400 == 0;}

static int Dtab[2][13] =
{
  {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
  {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
};

Date * Date::interval(const Date& d2)
{
   static Date result;
   int months, days, years, prev_month;
   
   // Compute the interval - assume d1 precedes d2
   years = d2.year - year;
   months = d2.month - month;
   days = d2.day - day;
   
   // Do obvious corrections (days before months!)
   //
   // This is a loop in case the previous month is
   // February, and days < -28.
   prev_month = d2.month - 1;
   while (days < 0)
   {
      // Borrow from the previous month
      if (prev_month == 0)
         prev_month = 12;
      --months;
      days += Dtab[isleap(d2.year)][prev_month--];
   }
   
   if {months < 0)
   {
      // Borrow from the previous year
      --years;
      months += 12;
   }
   
   /* Prepare output */
   result.month = months;
   result.day = days;
   result.year = years;
   return &result;
}

/* End of File */

Listing 3   使用Date类的示例
// tdate.cpp: Test the Date class

#include <stdio.h>
#include <stdlib.h>
#include "date.h"

main()
{
   Date d1, d2, *result;
   int nargs;
   
   // Read in two dates - assume 1st precedes 2nd
   fputs("Enter a date, MM/DD/YY> ",stderr);
   nargs = scanf("%d/%d/%d%*c", &d1.month,
     &d1.day, &d1.year);
   if (nargs != 3)
      return EXIT_FAILURE;
      
   fputs("Enter a later date, MM/DD/YY> ",stderr);
   nargs = scanf("%d/%d/%d%*c", &d2.month,
     &d2.day, &d2.year);
   if (nargs != 3)
      return EXIT_FAILURE;
   
   // Compute interval in years, months, and days
   result = d1.interval(d2);
   printf("years: %d, months: %d, days: %d\n",
      result->year, result->month, result->day);
   return EXIT_SUCCESS;
}

/* Sample Execution:
Enter a date, MM/DD/YY> 10/1/51
Enter a later date, MM/DD/YY> 11/14/92
years: 41, months: 1, days: 13
*/

/* End of File */

Listing 4  Listing 5所示的变化后的Date类的定义
// date2.h

struct Date
{
   int month;
   int day;
   int year;
   
   // Constructors
   Date();
   Date(int, int, int);
   
   Date * interval (const Date&);
};

/* End of File */

Listing 5   变化后的Date类

// date2.cpp

#include "date2.h"

inline int isleap(int y)
  {return y%4 == O && y%100 != 0 || y%400 == 0;}

static int Dtab [2][13] =
{
  {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
  {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
};

Date * Date::interval (const Date& d2)
{
   (same as in Listing 2)
}

Date::Date()
{
   month = day = year = 0;
}

Date::Date(int m, int d, int y)
{
   month = m;
   day = d;
   year = y;
}

/* End of File */

Listing 6 ： Date类的测试程序
// tdate2.cpp

#include <stdio.h>
#include <stdlib.h>
#include "date2.h"

main()
{
   int m, d, y, nargs;
   
   // Read in two dates - assume 1st precedes 2nd
   fputs("Enter a date, MM/DD/YY> ",stderr);
   nargs = scanf("%d/%d/%d%*c", &m,&d,&y);
   if (nargs != 3)
      return EXIT_FAILURE;
   Date d1(m,d,y);
   
   fputs("Enter a later date, MM/DD/YY> ",stderr);
   nargs = scanf("%d/%d/%d%*c", &m,&d,&y);
   if (nargs != 3)
      return EXIT_FAILURE;
   Date d2(m,d,y);
   
   // Compute interval in years, months, and days
   Date *result = d1.interval(d2);
   printf("years: %d, months: %d, days: %d\n",
      result->year, result->month, result->day);
   return EXIT_SUCCESS;
}
/* End of File */

Listing 7   将成员函数的实现放到类定义中去
// date2.h

struct Date
{
   int month;
   int day;
   int year;
   
   // Constructors
   Date()
     {month = day = year = 0;}
   Date(int m, int d, int y)
     {month = m; day = d; year = y;}
   
   Date * interval(const Date&);
};

/* End of File */

Listing 8   使用存取函数获取变量值的类定义
// date3.h

struct Date
{
private:
   int month;
   int day;
   int year;

public:
   // Constructors
   Date()
     {month = day = year = 0;}
   Date(int m, int d, int y)
     {month = m; day = d; year = y;}
   
   // Accessor Functions
   int get_month() const
     {return month;}
   int get_day() const
     {return day;}
   int get_year() const
     {return year;}
   
   Date * interval(const Date&) const;
};

/* End of File */

Listing 9   用 class 代替 struct 的类定义
// date3.h

class Date
{
   int month;
   int day;
   int year;

public:
   // Constructors
   Date()
     {month = day = year = 0;}
   Date(int m, int d, int y)
     {month = m; day = d; year = y;}
   
   // Accessor Functions
   int get_month() const
     {return month;}
   int get_day() const
     {return day;}
   int get_year() const
     {return year;}
   
   Date * interval(const Date&) const;
};

/* End of File */

Listing 10   对第三种版本日期类的测试

// tdate3. cpp
#include <stdio.h>
#include <stdlib.h>
#include "date3.h"
main()
{
   int m, d, y, nargs;
   
   // Read in two dates - assume 1st precedes 2nd
   fputs("Enter a date, MM/DD/YY> ",stderr);
   nargs = scanf("%d/%d/%d%*c", &m,&d,&y);
   if (nargs != 3)
      return EXIT_FAILURE;
   Date d1(m,d,y);
   
   fputs("Enter a later date, MM/DD/YY> ",stderr);
   nargs = scanf("%d/%d/%d%*c", &m,&d,&y);
   if (nargs != 3)
      return EXIT_FAILURE;
   Date d2(m,d,y);
   
   // Compute interval in years, months, and days
   Date *result = d1.interval(d2);
   printf("years: %d, months: %d, days: %d\n",
      result->get_year (),
      result->get_month (),
      result->get_day ());
   return EXIT_SUCCESS;
}
/* End of File */