Question

Is there any system defined function to compare two dates in C/C++?

Thanks

Answer 1

1. convert the date (you pick the format) to seconds since the start of the era. use strptime and mktime.
2. compare the two time_t (seconds) values.
   example using MON-DD-YYYY format:

CODE:

#include <time.h>
time_t to_seconds(const char *date)
{
    struct tm storage={0,0,0,0,0,0,0,0,0};
    char *p=NULL;
    time_t retval=0;

    p=(char *)strptime(date,"%d-%b-%Y",&storage);
    if(p==NULL)
    {
            retval=0;
    }
    else
    {
            retval=mktime(&storage);
    }
    return retval;
}

int main()
{
  char *date1="20-JUN-2006";
  char *date2="21-JUN-2006";
  time_t d1=to_seconds(date1);
  time_t d2=to_seconds(date2);

  printf("date comparison: %s %s ",date1,date2);
  if(d1==d2) printf("equal\n");
  if(d2>d1)  printf("second date is later\n");
  if(d2<d1)  printf("seocnd date is earlier\n");
 return 0;
}