#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <utmp.h>
#include <string.h>
#include <pwd.h>
#include <unistd.h>
#include <errno.h>

#ifdef LINUX
#include <sys/stat.h>
#endif

#include <fcntl.h>

#define MAX_TTY 20

struct utmp    uinfo[MAX_TTY];

int who_am_i(void);

int who_am_i(void)
{
  int fd, in = 0;
  struct passwd *pwd;
  struct utmp user;

  char login[UT_NAMESIZE+1];

  if ((pwd = getpwuid(geteuid())) == NULL)
    (void)strcpy(login, "unknown");
  else
    (void)strcpy(login, pwd->pw_name);

  if ((fd = open(_PATH_UTMP, O_RDONLY)) < 0) {
    perror(_PATH_UTMP);
    return -1;
  }

  (void)memset(&uinfo, 0, sizeof (uinfo));

  while(read(fd, &user, sizeof(user)) == sizeof(user)) 
    if (strncmp(user.ut_name, login, UT_NAMESIZE) == 0) {
      if (in == MAX_TTY) {
        return in;
      } else { 
        uinfo[in++] = user;
      }
    }

  close(fd);

  return 0;
} 

int main(void)
{
  if (who_am_i() == -1) {
    exit(EXIT_FAILURE);
  }

  exit(EXIT_SUCCESS);
}