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From: gwyn@smoke.brl.mil (Doug Gwyn)
Newsgroups: comp.lang.c
Subject: Re: Question about perror
Keywords: perror(), ansi C, posix
Message-ID: <14617@smoke.brl.mil>
Date: 30 Nov 90 10:08:55 GMT
References: <1990Nov28.152146.19560@ssd.kodak.com> <14603@smoke.brl.mil> <4573@oasys.dt.navy.mil>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 15

In article <4573@oasys.dt.navy.mil> stuart@oasys.dt.navy.mil (Stuart Pearlman) writes:
>Is perror() specified in the ansi C standard?  I avoid using perror()
>after library routines such as fopen() because they can fail for other
>reasons besides the system calls they make failing.  Are any of the
>library functions specified in the standard guaranteed to set errno?
>(Is errno even guaranteed to exist?)  What about posix 1003.1?  Does
>it specify what functions you can call perror() after?

perror() is required for ANSI C conformance.  errno is required, but
only a few of the standard functions (mainly math functions) are
required to set errno (upon certain conditions).  IEEE Std 1003.1
specifies that errno is to be set for error returns from a large
number of functions (mainly those normally implemented on UNIX as
genuine system calls).  The allowable values of errno (<errno.h>
macros) are specified for each function.