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From: daveb@geac.UUCP
Newsgroups: comp.lang.c
Subject: Re: Question on ANSI C compatibility
Message-ID: <1804@geac.UUCP>
Date: Wed, 11-Nov-87 10:48:42 EST
Article-I.D.: geac.1804
Posted: Wed Nov 11 10:48:42 1987
Date-Received: Fri, 13-Nov-87 06:33:21 EST
References: <10224@brl-adm.ARPA> <9272@mimsy.UUCP>
Reply-To: daveb@geac.UUCP (Dave Collier-Brown)
Organization: The little blue rock next to that twinkly star.
Lines: 47

In article <9272@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes:
| 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:
|  ...
| 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); }
| 	...

   There are several (methinks five) disjoint sets of return values:
	1) functions which return 0 or ERR (-1).
	2) functions which return NULL or a valid string.
	3) functions which return EOF (-1) or a valid character.
	4) functions which return a valid positive char/int or a
	   negative char/int as a specific error indication.
	5) functions which return a boolean value (0 or non-zero).

   They also may affect errno: type (1) almost always does, (2) and
(3) sometimes do. 
   Any function which sets errno is a candidate for (a) dullness and
(b) order-of-error related bugs [ie, "not a typewriter"].

    Types (2) through (5) sound like they're not dull, but
[fs]printf is a member of (4), sorta.

   Can we come up with a criteria for "dullness" which lint can
infer by itself? if necessary from the presence of "extern int
errno; return ERR" in a lintlibrary entry?  Or can someone suggest a
better/more-general way?

 --dave

-- 
 David Collier-Brown.                 {mnetor|yetti|utgpu}!geac!daveb
 Geac Computers International Inc.,   |  Computer Science loses its
 350 Steelcase Road,Markham, Ontario, |  memory (if not its mind)
 CANADA, L3R 1B3 (416) 475-0525 x3279 |  every 6 months.