#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
int main(int argc, char **argv) {
  setvbuf(stdout, NULL, _IONBF, 0);

  if (argc != 2) {
    fprintf(stderr, "Wrong argument count!\n");
    return 1;
  }

  int fd = open(argv[1], O_RDWR);
  if (fd == -1) {
    perror("Opening the file failed");
    return 1;
  }

  int cnt, pos;
  char buf[16];

  pos = lseek(fd, 0, SEEK_CUR);
  printf("Pos upon opening: %d\n", pos);

  cnt = read(fd, buf, 16);
  printf("First 16 bytes: ");
  write(1, buf, cnt);

  pos = lseek(fd, 0, SEEK_CUR);
  printf("\nPos before 16-byte write: %d\n",
         pos);

  cnt = write(fd, "Kilroy was here ", 16);

  pos = lseek(fd, 0, SEEK_CUR);
  printf("Pos after  16-byte write: %d\n",
         pos);

  close(fd);

  return 0;
}