Strange return codes from old but good C program
mail at ozzmosis.com
Sun May 17 12:42:28 UTC 2015
On Sun 2015-05-17 22:16:14 UTC+1000, Ian Smith (smithi at nimnet.asn.au) wrote:
> I'm hoping someone can help me figure out the behaviour of a C program
> executed repeatedly from a shell invoked by my freepascal program.
> If anyone might care to download <http://www.moshier.net/de118i-2.zip>
> (258071 bytes), unzip it and run 'make', the supplied makefile - a copy
> of unixl.mak - should provide ssystem compiled for long double precision
> maths, just as I wanted, with the following output from gcc from FreeBSD
> 4.5 to 9.3-RELEASE. (If clang has trouble on 10.X, please let me know)
That makefile defaults to gcc but allows you to build it with clang
(which spits out a bunch of warnings similar to gcc) using:
make -f unixl.mak CC=clang
> smithi at x200:~/de118i-2 % make
> gcc -O2 -c ssystem.c
> ssystem.c: In function 'resstate':
> ssystem.c:150: warning: incompatible implicit declaration of built-in
> function 'exit'
> ssystem.c: In function 'main':
> ssystem.c:180: warning: incompatible implicit declaration of built-in
> function 'malloc'
stdlib.h provides prototypes for exit() and malloc().
> ssystem runs as well as ever, these warnings indicate no functional
> issues, but they do highlight the author's poor (but unsurprising in
> 1993, last updated 2004) choice of return codes both for real errors
> (malloc, file I/O, and maths div by zero, bad args for trig functions
> and such) which mostly exit(1) but some return 0 (!) - but when ending
> successfully it returns _usually_ 22, but sometimes 11, or 10, both seen
> so far, consistently when run with the same (different) parameters.
The code looks like ancient K&R C, which was a lot more relaxed with
syntax than modern ISO C compilers. Even by 1993, most C developers
had moved on from K&R.
> What's worse is I can't figure out where in ssystem.c any return code
> might be set on completion of main(), which is just declared as:
This is fine in K&R, but the ISO C prototype for main() without arguments is:
> and ends with the last of its results and (accuracy) errors printf()s:
> ii += 6;
> #if FPESHOW # floating point debug, here set to 0
> } /* end of main program */
> No variables called rc or anysuch .. so what sets these odd retcodes?
Normally you'd use a return statement, eg.
#include <stdio.h> /* prototype for printf() */
printf("Hello world.\n"); /* say hi */
return 0; /* return zero to the OS */
I haven't checked the standard but it's plausible that the ISO C spec
allows a random return code if none is given, especially if no
prototype for main() is provided.
There may be tools around to convert K&R C code to ANSI/ISO C syntax,
rather than trying to do it by hand. The code may still need some
tweaking, though, eg. return 0 from main().
> I'd be grateful for any clue. So far I assume any return code > 1 is
> success, so far so good - but it doesn't feel deterministic enough :)
> cheers, Ian (please cc me, I'm subscribed to the digest)
Pretty sure I know you from FidoNet, years ago. Also Trev Roydhouse.
AUST_C_HERE, or another echo, maybe?
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