incomplete arglist in C (was: volatile (Really BSD signal handler))

[Alan J Rosenthal]

Discussing signal handlers, Karl Heuer wrote something like

>static void catch(int signo) { gotcha = 1; }

Someone else corrected him and said it should be

>static void catch(int signo, code; struct sigcontext *scp) { gotcha = 1; }

and added:

>In the past I've had my signal handler return to random pieces of
>code by not having the correct definition.

Discussing whether or not such behaviour is a bug, Eddie Wyatt wrote:

>  It's questionable whether its a bug or not.  The Sun man page reads:
>
>     The handler routine can be declared:
>
>	  handler(sig, code, scp)
>	  ...

and then emphasized the impreciseness of the word ``can''.


My addition to this conversation is as follows:

Before ANSI C it was accepted that a function could be called with more
arguments than it itself declared as formals.  So for example you could
have a call to "f(a,b)" where f() was defined beginning "int f(x) int x;",
and `x' would get the value of the expression `a', `b' would be
calculated and discarded, and Nothing Bad would happen.  It was even
somewhat accepted that you could do the reverse so long as f() itself
didn't access its arguments; so, for example, with f() defined as
follows:

	int f(a,b)
	    int a,b;
	{
	    if(a == 1)
		return(5);
	    else
		return(b);
	}

calls of f(1) would be legitimate.

I would also like to point out that K&R says, on page 71, although
admittedly not at all definitively:

	``It is generally safe to deal with a variable number of
	arguments if the called function doesn't use an argument which
	was not actually supplied, and if the types are consistent.''

One further point:  It may be argued that this doesn't apply to signal
handlers, but I would say that conceptually there is a system function
called when a signal happens, which in turn calls the user function.
Therefore the user function is called using the C calling conventions
no matter what happens at the system level when a signal happens.

ajr
-- 
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