Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!lll-winken!uunet!mcvax!hp4nl!dutrun!vlruo02
From: vlruo02@dutrun.UUCP (Ge van Geldorp)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Ctrl-C Echo
Summary: get ctrl-c.c
Keywords: ctrl-c trapping, SIGINT
Message-ID: <677@dutrun.UUCP>
Date: 4 Apr 89 16:11:27 GMT
References: <1167@optilink.UUCP> <7542@fluke.COM>
Reply-To: vlruo02@dutrun.UUCP (G.v.Geldorp)
Organization: Delft University of Technology, The Netherlands
Lines: 42

In article <7542@fluke.COM> mason@tc.fluke.COM (Nick Mason) writes:
>In article <1167@optilink.UUCP> cramer@optilink.UUCP (Clayton Cramer) writes:
>>I'm using signal(SIGINT, SIG_IGN) to disable control-C processing from
>>an application, and it works.  But the second and third times I type
>>control-C, the ^C\r\n are echoed to the screen, even though there is
>>no control-C processing taking place.  Any idea who is producing the
>>screen output, and how to stop it?
>
>
>I'm doing something similar in my code to capture ctrl-C.  The capture
>works great, but as you also found ^C\r\n is echoed to the screen.
>
>After looking into this a great deal I believe that the echo is coming
>from the BIOS and the INT9 keyboard interrupt handler.  If this is 
>true then the only way to get rid of it is to write your own
>keyboard handler routine.

It's the CON device driver which writes the ^C\r\n. The good news is
that there are ways to avoid this.
If you want to disable Ctrl-c completely, get the <MSDOS.C>CTRL-C.C
package from SIMTEL20. The routines in this package (which was written
by John Galvin, galvin@circle.UUCP) basicly put the CON device in raw
mode, using dos function 0x44 (IOCTL). 
If you want to act upon ctrl-c, but have the ^C\r\n suppressed, things
are slightly more difficult. The ^C\r\n string is written to standard
output. If you can do without standard output, open the NUL device. Use
the file descriptor obtained from this call with a dup2 call to have
stdout redirected to NUL. Now, the CON driver can write ^C\r\n if it
wants to, but it won't end on your screen.
Code fragment:

   int nulfh;

   nulfh = open("nul", O_WRONLY, 0644);   /* get new file descriptor */
   fflush(stdout);                        /* flush any remaining chars */
   dup2(nulfh, 1);                        /* redirect stdout to NUL */
   close(nulfh);                          /* clean up */

Hope this helps.

Ge van Geldorp.
(...!mcvax!hp4nl!dutrun!vlruo02)