#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <ctype.h>

#define DAY(n)	(n == 0) ? "Sun" :\
		(n == 1) ? "Mon" :\
		(n == 2) ? "Tue" :\
		(n == 3) ? "Wed" :\
		(n == 4) ? "Thu" :\
		(n == 5) ? "Fri" :\
		(n == 6) ? "Sat" : "None"
#define MON(n)	(n == 0) ? "Jan" :\
		(n == 1) ? "Feb" :\
		(n == 2) ? "Mar" :\
		(n == 3) ? "Apr" :\
		(n == 4) ? "May" :\
		(n == 5) ? "Jun" :\
		(n == 6) ? "Jul" :\
		(n == 7) ? "Aug" :\
		(n == 8) ? "Sep" :\
		(n == 9) ? "Oct" :\
		(n ==10) ? "Nov" :\
		(n ==11) ? "Dec" : "None"

char *timef(char *, time_t);

int main(int argc, char *argv[]) {
  printf("%s\n", timef("%w %m %d %H:%M:%S %y", time(0)));
  printf("%s\n", timef("%T (%t %p (%P)), %D", time(0)));
  printf("%s\n", timef("%t (use arg)", (argc < 2) ? time(0) : atoi(argv[1])));
  printf("%s\n", timef("day: %d\nmon: %m\nweek: %w\nyear: %y", time(0)));
  return 0;
}

char *timef(char *format, time_t sse) {
  int i, t;
  char *buffer = malloc(strlen(format)+100);
  struct tm *time_s;

  memset(buffer, 0, strlen(buffer));
  time_s = localtime(&sse);

  for (i=0; i<strlen(format); i++) {
    if (format[i] == '%') {
      switch(format[++i]) {
	case 'H': sprintf(buffer, "%s%2.2d", buffer, time_s->tm_hour);
		break;
	case 'M': sprintf(buffer, "%s%2.2d", buffer, time_s->tm_min);
		break;
	case 'S': sprintf(buffer, "%s%2.2d", buffer, time_s->tm_sec);
		break;
	case 'y': sprintf(buffer, "%s%d", buffer, time_s->tm_year+1900);
		break;
	case 'w': sprintf(buffer, "%s%s", buffer, DAY(time_s->tm_wday));
		break;
	case 'm': sprintf(buffer, "%s%s", buffer, MON(time_s->tm_mon));
		break;
	case 'd': sprintf(buffer, "%s%d", buffer, time_s->tm_mday);
		break;
	case 'D': sprintf(buffer, "%s%d/%d/%d", buffer, time_s->tm_mday,
							time_s->tm_mon+1,
							time_s->tm_year+1900);
		break;
	case 'T': sprintf(buffer, "%s%2.2d:%2.2d:%2.2d", buffer,
							time_s->tm_hour,
							time_s->tm_min,
							time_s->tm_sec);
		break;
	case 't': sprintf(buffer, "%s%d:%2.2d", buffer, (time_s->tm_hour <= 12)
							? time_s->tm_hour
							: time_s->tm_hour-12,
							time_s->tm_min);
		break;
	case 'p': sprintf(buffer, "%s%s", buffer, (time_s->tm_hour <= 12)
							? "am"
							: "pm");
		break;
	case 'P': sprintf(buffer, "%s%s", buffer, (time_s->tm_hour <= 12)
							? "AM"
							: "PM");
		break;
	case '%': sprintf(buffer, "%s%%", buffer);
		break;
      }
      i++;
    }

    sprintf(buffer, "%s%c", buffer, format[i]);
  }

  return buffer;
}