clock/clock.c

/* clock.c - Public Domain - It's a digital clock
EXEC:
  cc -O1 -s -pipe -Wall -Wextra -Wpedantic $CPPFLAGS -o clock clock.c && gzexe clock
:STOP */
#include <time.h>
#include <stdio.h>
#include <unistd.h>

#ifndef CLEAR
# define CLEAR "\033[2J"
#endif

#ifndef CLEAR_DUMB
# define CLEAR_DUMB "\n"
#endif

#ifndef PERIOD
# define PERIOD 5
#endif

char * hmstime(struct tm * tm)
{
  static char time[9];
  sprintf(time, "%.2d:%.2d:%.2d",
          tm->tm_hour, tm->tm_min, tm->tm_sec);
  return time;
}

int
main(void)
{
  struct tm * tm;
  time_t now;
  int sec;

  puts("Type C-c to exit.\n");

  for (;;)
  {
    time(&now);
    tm = gmtime(&now);
    /* Junk character may be printed, this is the time to get a new terminal. */
    printf(CLEAR " %s\n" CLEAR_DUMB, hmstime(tm));
    sec = tm->tm_sec % PERIOD;
    sleep(!sec ? PERIOD : PERIOD - sec);
  }

  return 0;
}