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From: brad@SSD.CSD.HARRIS.COM (Brad Appleton)
Newsgroups: comp.lang.c
Subject: Re: Catching Signals in 'C'
Summary: Subtlety between BSD and AT&T signals
Message-ID: <1103@travis.csd.harris.com>
Date: 28 Sep 90 20:31:56 GMT
References: <2901@idunno.Princeton.EDU> <2905@idunno.Princeton.EDU> <2910@idunno.Princeton.EDU>
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Organization: Harris Computers Systems Division, Fort Lauderdale,FL
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There is a difference between AT&T and BSD signal calls (that has already been
hinted at) that is important to know in this situation:

When you set-up a signal handler in the AT&T universe, your handler
is only called the very next time that signal is caught and subsequent
calls refer back to the default handler unless you reset your handler
in the handler-code.

When you set up a signal handler in the BSD universe, your handler
is called for all subsequent trappings of that signal unless you
specifically reset the handler to be something else in the handler-code.

The following code fragment might be used to set up a minimal
Control-C handler that would be portable accross Unixes (assuming that
"att_universe" is #defined for an AT&T system and "ucb_universe" is 
#defined for a BSD system):

	#include <stdio.h>
	#include <signal.h>

	void ctrl_c_handler()
	{
	  printf( "\n+++ in ctrl_c_handler() +++\n" );

	#ifdef att_universe
		/* need to reset this handler so we can trap the signal again */
	  if ( signal( SIGINT, ctrl_c_handler ) < 0 )
	    perror( "unable to set-up SIGINT handler" );
	#endif

	}

	main()
	{
	  if ( signal( SIGINT, ctrl_c_handler ) < 0 )
	    perror( "unable to set-up SIGINT handler" );

	  printf( "about to loop forever\n\n" );
	  while (1);
	}


Anybody know about DOS and/or VMS???
______________________ "And miles to go before I sleep." ______________________
 Brad Appleton        brad@travis.ssd.csd.harris.com   Harris Computer Systems
                          ...!uunet!hcx1!brad          Fort Lauderdale, FL USA
~~~~~~~~~~~~~~~~~~~~ Disclaimer: I said it, not my company! ~~~~~~~~~~~~~~~~~~~