Section (3) perror
perror — print a system error message
||const char *s
#include <errno.h> const char * const sys_errlist; int sys_nerr; int errno; /* Not really declared this way; see errno(3) */
produces a message on standard error describing the last
error encountered during a call to a system or library
s is not
NULL and *
s is not a
null byte (_zsingle_quotesz_ _zsingle_quotesz_)), the argument string
s is printed, followed by a
colon and a blank. Then an error message corresponding to the
current value of
errno and a
To be of most use, the argument string should include the name of the function that incurred the error.
The global error list
sys_errlist, which can be indexed by
errno, can be used to obtain the
error message without the newline. The largest message number
provided in the table is
sys_nerr−1. Be careful when directly
accessing this list, because new error values may not have
been added to
sys_errlist is nowadays
deprecated; use strerror(3) instead.
When a system call fails, it usually returns −1 and
sets the variable
errno to a
value describing what went wrong. (These values can be found
Many library functions do likewise. The function
perror() serves to translate this error
code into human-readable form. Note that
errno is undefined after a successful system
call or library function call: this call may well change this
variable, even though it succeeds, for example because it
internally used some other library function that failed.
Thus, if a failing call is not immediately followed by a call
perror(), the value of
errno should be saved.
For an explanation of the terms used in this section, see attributes(7).
||Thread safety||MT-Safe race:stderr|
errno: POSIX.1-2001, POSIX.1-2008, C89, C99,
sys_errlist derive from BSD, but
are not specified in POSIX.1.
This page is part of release 5.04 of the Linux
man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
Copyright (c) 1994 Michael Haardt (michaelmoria.de), 1994-06-04
Copyright (c) 1995 Michael Haardt
Copyright (c) 1996 Andries Brouwer (aebcwi.nl), 1996-01-13
This is free documentation; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of
the License, or (at your option) any later version.
The GNU General Public License_zsingle_quotesz_s references to object code
and executables are to be interpreted as the output of any
document formatting or typesetting system, including
intermediate and printed output.
This manual is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public
License along with this manual; if not, see
1996-01-13 aeb: merged in some text contributed by Melvin Smith
(msmithfalcon.mercer.peachnet.edu) and various other changes.
Modified 1996-05-16 by Martin Schulze (joeyinfodrom.north.de)