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From: mouse@mcgill-vision.UUCP
Newsgroups: comp.lang.c
Subject: Re: A better perror() (Was: Re: Accessing argc ...)
Message-ID: <883@mcgill-vision.UUCP>
Date: Mon, 7-Sep-87 05:44:33 EDT
Article-I.D.: mcgill-v.883
Posted: Mon Sep  7 05:44:33 1987
Date-Received: Sat, 19-Sep-87 05:40:51 EDT
References: <22@flmis06.ATT.COM> <28700015@ccvaxa> <853@mcgill-vision.UUCP> <1427@chinet.UUCP>
Organization: McGill University, Montreal
Lines: 34

In article <1427@chinet.UUCP>, rlk@chinet.UUCP (Richard Klappal) writes:
> In article <1351@killer.UUCP> molly@killer.UUCP (Molly Fredericks) writes:
>> In article <853@mcgill-vision.UUCP>, mouse@mcgill-vision.UUCP (der Mouse) writes:
>>> In article <28700015@ccvaxa>, aglew@ccvaxa.UUCP quotes:
>>>> I have always thought that perror(str) was silly - sometimes I
>>>> want str to be the command name, sometimes the command plus all
>>>> arguments...
>>> Wish perror() were printflike, perhaps like syslog() [which]
>>> accepts a printf format, except that %m means insert
>>> sys_errlst[errno].
(Or close to that, at least - if errno is an unknown error, it inserts
"Unknown error" (stock perror) or "Unknown error (%d)" with the number
inserted (my perror).)
> My solution to this is
> 	extern int	errno;
> 	extern char	*sys_errlist[];
> 	#define	SYS_ERRMSG	sys_errlist[errno]
> 	:
> 	printf("..whatever..: %s\n", args_for_whatever, SYS_ERRMSG);
> This method assumes that 'errno' has been correctly supplied a value.
> (e.i.[sic], That an error occured.)

It also assumes that the value in errno is a valid index into
sys_errlist!  The warning in the man page is there for a reason.
Wouldn't it be just wonderful to see

Cannot open input file foo.in: ^ZA^DZPPPYPYXU^I^S^B^QzQYh^Y^CB^DYPYoZ#^B

because whoever did the UNIX port your code happens to be compiled on
neglected to add their new error codes to sys_errlist[]?

					der Mouse

				(mouse@mcgill-vision.uucp)