Listing 1. An Example of an Implementation of kbhit()

#include <sys/select.h>

int kbhit(void)
{
  struct timeval tv;
  fd_set read_fd;

  /* Do not wait at all, not even a microsecond */
  tv.tv_sec=0;
  tv.tv_usec=0;

  /* Must be done first to initialize read_fd */
  FD_ZERO(&read_fd);

  /* Makes select() ask if input is ready:
   * 0 is the file descriptor for stdin    */
  FD_SET(0,&read_fd);

  /* The first parameter is the number of the
   * largest file descriptor to check + 1. */
  if(select(1, &read_fd,
            NULL, /*No writes*/
            NULL, /*No exceptions*./
            &tv)
     == -1)
    return 0;  /* An error occured */

  /*  read_fd now holds a bit map of files that are
   * readable. We test the entry for the standard
   * input (file 0). */
  if(FD_ISSET(0,&read_fd))
    /* Character pending on stdin */
    return 1;

  /* no characters were pending */
  return 0;
}