Non-Trivial Class in C++

This C++ date class is intended to illustrate how to write a non- trivial class in C++.

Even though this class is non-trivial, it is still simple enough for a new C++ programmer to follow all of the details of the C++ program.  Initially the constructor sets the date to current date and format to 1. This class also makes use of #ifndef directive and DOS System calls to get the date.

#ifndef DATE_H
#define DATE_H


class date {
protected:
   int month;                  // 1 through 12
   int day;                    // 1 through max_days
   int year;                   // 1500 through 2200
   static char out_string[25]; // format output area
   static char format;         // format to use for output


         // Calculate how many days are in any given month
         // Note - This is a private method which can be called only
         //        from within the class itself
   int days_this_month(void);


public:
         // Constructor - Set the date to the current date and set
         //               the format to 1
   date(void);


         // Set the date to these input parameters
         //  if return = 0 ---> All data is valid
         //  if return = 1 ---> Something out of range
   int set_date(int in_month, int in_day, int in_year);


         // Get the month, day, or year of the stored date
   int get_month(void) { return month; };
   int get_day(void)   { return day;   };
   int get_year(void)  { return year;  };


         // Select the desired string output format for use when the
         //  get_date_string is called
   void set_date_format(int format_in) { format = format_in; };


         // return an ASCII-Z string depending on the stored format
         //   format = 1    Aug 29, 1991
         //   format = 2    8/29/91
         //   format = 3    8/29/1991
         //   format = 4    29 Aug 1991    Military time
         //   format = ?    Anything else defaults to format 1
   char *get_date_string(void);


         // return Jan Feb Mar Apr etc.
   char *get_month_string(void);
};


#endif


//end of the date.h


//date.cpp file implementation
// This file contains the implementation for the date class.


#include <sprintf.h>       // Prototype for sprintf
#include <date.h>        // Prototypes for the current date
#include "date.h"


char date::format;         // This defines the static data member
char date::out_string[25]; // This defines the static string


         // Constructor - Set date to current date, and
         //               set format to the default of 1
date::date(void)
{
time_t time_date;
struct tm *current_date;


   time_date = time(NULL);                // DOS system call
   current_date = localtime(&time_date);  // DOS system call
   month = current_date->tm_mon + 1;
   day = current_date->tm_mday;
   year = current_date->tm_year + 1900;
   format = 1;
}



         // Set the date to these input parameters
         //  if return = 0 ---> All data is valid
         //  if return = 1 ---> Something out of range
int date::set_date(int in_month, int in_day, int in_year)
{
int temp = 0;
int max_days;
                      // The limits on the year are purely arbitrary
   if (in_year < 1500) { // Check that the year is between year = 1500; // 1500 and 2200 temp = 1; } else { if (in_year > 2200) {
         year = 2200;
         temp = 1;
      } else
         year = in_year;
   }


   if(in_month < 1) { // Check that the month is between month = temp = 1; // 1 and 12 } else { if (in_month > 12) {
         month = 12;
         temp = 1;
      } else
         month = in_month;
   }


   max_days = days_this_month();
   if (in_day < 1) { // Check that the day is between day = temp = 1; // 1 and max_days } else { if (in_day > max_days) {
         day = max_days;
         temp = 1;
      } else
         day = in_day;
   }


   return temp;
}


static char *month_string[13] = {" ", "Jan", "Feb", "Mar", "Apr",
                                      "May", "Jun", "Jul", "Aug",
                                      "Sep", "Oct", "Nov", "Dec"};


         // return Jan Feb Mar Apr etc.
char *date::get_month_string(void)
{
   return month_string[month];
}

        // return an ASCII-Z string depending on the stored format
         //   format = 1    Aug 29, 1991
         //   format = 2    8/29/91
         //   format = 3    8/29/1991
         //   format = 4    29 Aug 1991    Military time
         //   format = ?    Anything else defaults to format 1
char *date::get_date_string(void)
{
   switch (format) {
                       // This printout assumes that the year will be
                       //  between 1900 and 1999
      case 2  : sprintf(out_string, "%02d/%02d/%02d",
                                            month, day, year - 1900);
                break;


      case 3  : sprintf(out_string, "%02d/%02d/%04d",
                                                   month, day, year);
                break;


      case 4  : sprintf(out_string, "%d %s %04d",
                                     day, month_string[month], year);
                break;


      case 1  : // Fall through to the default case
      default : sprintf(out_string, "%s %d, %04d",
                                     month_string[month], day, year);
                break;
   }
   return out_string;
}





int days[13] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};


         // Since this is declared in the private part of the class
         //  header is is only available for use within the class.
         //  It is hidden from use outside of the class.
int date::days_this_month(void)
{
   if (month != 2)
      return days[month];


   if (year % 4)       // Not leap year
      return 28;
   if (year % 100)     // It is leap year
      return 29;
   if (year % 400)     // Not leap year
      return 28;
   return 29;          // It is leap year
}