// Turn cbreak on or off.  man stty says cbreak is just -icanon and
// -cbreak is just icanon.  man termios has a section "Canonical and
// noncanonical mode" and explains that the `ICANON` flag in `c_lflag`
// (“local mode”) controls it:
/*
    In noncanonical mode input is available immediately (without the
    user having to type a line-delimiter character), no input
    processing [ISIG and ECHO*] is performed, and line editing is
    disabled.  The read buffer will only accept 4095 chars; this
    provides the necessary space for a newline char if the input mode
    is switched to canonical.  The settings of MIN (c_cc[VMIN]) and
    TIME (c_cc[VTIME]) determine the circumstances in which a read(2)
    completes; (...)
 */
// cbreak is what I want for my terminal Tetris.
#include <sys/ioctl.h>
#include <stdio.h>
#include <termios.h>
#include <stddef.h>

int main(int argc, char **argv)
{
  struct termios ios = {0};
  printf("TCGETS = 0x%x, struct termios is %zd bytes.\n", TCGETS, sizeof ios);
  if (ioctl(0, TCGETS, &ios)) {
    perror("TCGETS");
    return 1;
  }
  printf("c_lflag of size %zd is at offset %zd with value 0x%x.\n",
         sizeof ios.c_lflag,
         (size_t)offsetof(struct termios, c_lflag),
         (int)ios.c_lflag);
  ios.c_lflag ^= ICANON;
  printf("ICANON is 0x%x.  After flipping it c_lflag is 0x%x.\n",
         ICANON, ios.c_lflag);
  ios.c_lflag ^= ECHO;
  printf("ECHO is 0x%x.  After flipping it c_lflag is 0x%x.\n",
         ECHO, ios.c_lflag);
  if (ioctl(0, TCSETS, &ios)) {
    perror("TCSETS");
    return 1;
  }
  printf("TCSETS (0x%x) ran OK.\n", TCSETS);
  return 0;
}