### 17.8 Noncanonical Mode Example ¶

Here is an example program that shows how you can set up a terminal device to read single characters in noncanonical input mode, without echo.

    #include <unistd.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <termios.h>

    /* Use this variable to remember original terminal attributes. */

    struct termios saved_attributes;

    void
    reset_input_mode (void)
    {
      tcsetattr (STDIN_FILENO, TCSANOW, &saved_attributes);
    }

    void
    set_input_mode (void)
    {
      struct termios tattr;

      /* Make sure stdin is a terminal. */
      if (!isatty (STDIN_FILENO))
        {
          fprintf (stderr, "Not a terminal.\n");
          exit (EXIT_FAILURE);
        }

      /* Save the terminal attributes so we can restore them later. */
      tcgetattr (STDIN_FILENO, &saved_attributes);
      atexit (reset_input_mode);

      /* Set the funny terminal modes. */
      tcgetattr (STDIN_FILENO, &tattr);
      tattr.c_lflag &= ~(ICANON|ECHO); /* Clear ICANON and ECHO. */
      tattr.c_cc[VMIN] = 1;
      tattr.c_cc[VTIME] = 0;
      tcsetattr (STDIN_FILENO, TCSAFLUSH, &tattr);
    }

    int
    main (void)
    {
      char c;

      set_input_mode ();

      while (1)
        {
          read (STDIN_FILENO, &c, 1);
          if (c == '\004')          /* C-d */
            break;
          else
            write (STDOUT_FILENO, &c, 1);
        }

      return EXIT_SUCCESS;
    }

This program is careful to restore the original terminal modes before exiting or terminating with a signal. It uses the `atexit` function (see Cleanups on Exit) to make sure this is done by `exit`.

The shell is supposed to take care of resetting the terminal modes when a process is stopped or continued; see Job Control. But some existing shells do not actually do this, so you may wish to establish handlers for job control signals that reset terminal modes. The above example does so.