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<h3 class="section">17.7 Noncanonical Mode Example</h3>

<p>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.

<pre class="smallexample">     #include &lt;unistd.h&gt;
     #include &lt;stdio.h&gt;
     #include &lt;stdlib.h&gt;
     #include &lt;termios.h&gt;
     
     /* <span class="roman">Use this variable to remember original terminal attributes.</span> */
     
     struct termios saved_attributes;
     
     void
     reset_input_mode (void)
     {
       tcsetattr (STDIN_FILENO, TCSANOW, &amp;saved_attributes);
     }
     
     void
     set_input_mode (void)
     {
       struct termios tattr;
       char *name;
     
       /* <span class="roman">Make sure stdin is a terminal.</span> */
       if (!isatty (STDIN_FILENO))
         {
           fprintf (stderr, "Not a terminal.\n");
           exit (EXIT_FAILURE);
         }
     
       /* <span class="roman">Save the terminal attributes so we can restore them later.</span> */
       tcgetattr (STDIN_FILENO, &amp;saved_attributes);
       atexit (reset_input_mode);
     
       /* <span class="roman">Set the funny terminal modes.</span> */
       tcgetattr (STDIN_FILENO, &amp;tattr);
       tattr.c_lflag &amp;= ~(ICANON|ECHO); /* <span class="roman">Clear ICANON and ECHO.</span> */
       tattr.c_cc[VMIN] = 1;
       tattr.c_cc[VTIME] = 0;
       tcsetattr (STDIN_FILENO, TCSAFLUSH, &amp;tattr);
     }
     
     int
     main (void)
     {
       char c;
     
       set_input_mode ();
     
       while (1)
         {
           read (STDIN_FILENO, &amp;c, 1);
           if (c == '\004')          /* <kbd>C-d</kbd> */
             break;
           else
             putchar (c);
         }
     
       return EXIT_SUCCESS;
     }
</pre>
   <p>This program is careful to restore the original terminal modes before
exiting or terminating with a signal.  It uses the <code>atexit</code>
function (see <a href="Cleanups-on-Exit.html#Cleanups-on-Exit">Cleanups on Exit</a>) to make sure this is done
by <code>exit</code>.

   <p>The shell is supposed to take care of resetting the terminal modes when
a process is stopped or continued; see <a href="Job-Control.html#Job-Control">Job Control</a>.  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.

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