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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: Question on ANSI C compatibility
Message-ID: <9272@mimsy.UUCP>
Date: Sun, 8-Nov-87 20:03:14 EST
Article-I.D.: mimsy.9272
Posted: Sun Nov  8 20:03:14 1987
Date-Received: Wed, 11-Nov-87 03:08:19 EST
References: <10224@brl-adm.ARPA>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 63

In article <10224@brl-adm.ARPA> RMANGALD%CLARKU.BITNET@wiscvm.wisc.EDU writes:
>... I'm not sure whether the ANSI standard requires what I don't
>want to do -- put a "(void)" in front of every function call where I'm
>throwing away the return value.

It does not *require* it, but it does permit a compiler to complain
about every such occurrence.

>It's a real pain to prefix all the "printf()"'s, "gets()"'s, etc. with
>"(void)", so could someone tell me ... whether it is good programming style?

For some functions, I would say yes; for others, I would say no.
For instance, the value from printf et alii indicates the number
of characters printed, or EOF (or < 0, not sure which) for error.
Hence one should test printf return values for errors or explicitly
state (via `(void)') that one is not concerned with any such error.
On the other hand, it is possible to test for error after calling
printf:

	fprintf(foil, fmt, arg);
	if (ferror(foil)) {
		/* foiled again */
		...

In this case the return value is indeed dull.

Some functions never return errors: strcpy, for instance, copies
its second argument on top of its first, then returns its first.
`(void) strcpy(to, from)' is only interesting if you have not
saved `to' anywhere else:

	char *
	stralloc(int len)
	{
		char *p = malloc(len + 1);

		if (p == NULL)
			stop("out of memory (stralloc)");
		return (p);
	}

	char *
	strsave(char *s)
	{

		return (strcpy(stralloc(strlen(s)), s));
	}

Unfortunately, there is no (standard) way to distinguish between
functions with `interesting' values and those with `dull' values.
Indeed, in 4BSD there is no way at all; this is something I intend
to change.  It looks as though it will be fairly easy to add to
lint a new pragma:

	...
	double	atof(s) char *s; { return (0.0); }
	int	strlen(s) char *s; { return (1); }
		/* DULLVALUE */
	char	*strcpy(to, from) char *to, *from; { return (to); }
	...
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris