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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.lang.c
Subject: Re: Talking of void ...
Message-ID: <32081@sun.uucp>
Date: Tue, 27-Oct-87 13:22:20 EST
Article-I.D.: sun.32081
Posted: Tue Oct 27 13:22:20 1987
Date-Received: Fri, 30-Oct-87 03:28:46 EST
References: <1400@mhres.mh.nl> <31905@sun.uucp> <1407@mhres.mh.nl>
Sender: news@sun.uucp
Lines: 36
Keywords: return void cast

> There are two reasons to return a value: one to keep lint from
> complaining, and the other reason is a matter of programming principles. If
> a function is typed, I always use an explicit return value. 

Which is precisely why "void ()" is the correct type for a signal handler
function, since the value it returns isn't used....

The only reason why it was "int ()" is that "void" didn't exist as a C data
type when the C-language version of the UNIX signal mechanism first appeared.
As such, "int ()" had to serve a dual purpose; it was used both for functions
returning "int" and for functions returning nothing.  (This unfortunately meant
that the C compiler could not complain about functions declared (explicitly or
implicitly) as "int" that didn't return values.)  Signal handlers *really*
aren't "int ()"; their data type can be best described as "poor man's 'void
()'".  Now that "void" is supported in most C implementations, the data type
has been changed to "void ()".

Given that, and given the problems you have with moving signal handlers that
really return a value to modern systems with the proper type for signal
handlers, it would be better *not* to consider signal handlers really to be
"int ()", treat them as "void ()" (just not declaring them as such on older
systems), and don't have them return a value.

As for "lint", well, for the same reason the C compiler doesn't complain about
"int ()" functions that don't return values, "lint" doesn't complain about them
either.  It only complains if a function returns a value sometimes but not
other times, or if a function returns no value but somebody uses the
non-existent value (another good reason for using "void" - the *compiler*
can reject code that attempts to use the non-existent "value" of a "void ()"
function).

(The C++ compiler (the 1.1 version, anyway) *will* give a warning if you have a
function declared as "int" that doesn't return a value.)
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com