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From: pfalstad@bow.Princeton.EDU (Paul John Falstad)
Newsgroups: comp.lang.c
Subject: Re: Catching Signals in 'C'
Message-ID: <2901@idunno.Princeton.EDU>
Date: 28 Sep 90 14:48:36 GMT
References: <1990Sep28.120043.17628@NCoast.ORG>
Sender: news@idunno.Princeton.EDU
Reply-To: pfalstad@bow.Princeton.EDU (Paul John Falstad)
Lines: 31

In article <1990Sep28.120043.17628@NCoast.ORG>, ramsey@NCoast.ORG (Cedric Ramsey) writes:
|> Hello peoplekind. I have a question about the behavior of the
|> signal function. Firstly, I want to trap the control-c, break,
|> and other interrupt keys the user may use to stop a program.
|> I did this by ;
|> 
|> main()
|> {
|>   signal (SIGINT, (*handler1) ());
|>   signal (SIGQUIT, (*handler2) ());
|>   ... 
|> }
|> 
|> 
|> But, when I type a control-c the program handles the signal as
|> expected; however, when I type the control-c a second time the program 
|> doesn't catch it and simply exits. 

I quote from K&R, p. 255:

"When a signal 'sig' subsequently occurs, the signal is __restored to its
default behavior__; then the signal-handler is called, as if by (*handler)(sig)."

The signal handler should reinstall itself before returning.  signal() apparently
does not act this way in my implementation (SunOS)...  Fortunately.

-- 
Here is the address to complain to:
pfalstad@phoenix.princeton.edu PLink:HYPNOS GEnie:P.FALSTAD CIS: 70016,1355
That address again,
sync@thumper.princeton.edu PLink:OHS738 GEnie:OHS738 CIS: 4128 143 1234 937