Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!ames!haven!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.lang.c
Subject: Re: Reporting errors from local libraries
Message-ID: <10407@smoke.BRL.MIL>
Date: 16 Jun 89 21:06:43 GMT
References: <9449@alice.UUCP> <Jun.8.14.27.29.1989.6740@math.rutgers.edu> <186@cbnewsd.ATT.COM> <25447@agate.BERKELEY.EDU>
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 21

In article <25447@agate.BERKELEY.EDU> bks@ALFA.berkeley.edu ( Brad Sherman ) writes:
>Where is the actual space for "errno" allocated?

The usual implementation is for the C library to contain a module that
defines storage for it, for example what you get when you compile:

	/* errno.c -- C library source for the "errno" data module */
	int errno;

(Actually, the module usually also contains an secret run-time support
function that is used to log an error into errno and return a -1 value
from the failed system call.)

>If one has N libraries and all functions in these libraries return
>0 on success and -1 on failure, and one wishes, say, to set an (extern)
>integer "Localerrno" to provide additional info on failure, what is the
>guruish way to proceed?

The "errno" approach is a mistake, and I strongly recommend not returning
values via external global variables.  Use a better function interface,
for example return 0 on success and non-zero error code on failure.