Name

perror — print a system error message

Synopsis

#include <stdio.h>
void perror( const char *s);
 
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
sys_errlist, sys_nerr: _BSD_SOURCE
#include <errno.h>

const char *sys_errlist[];
int sys_nerr;
int errno;
  

DESCRIPTION

The routine perror() produces a message on the standard error output, describing the last error encountered during a call to a system or library function. First (if s is not NULL and *s is not a null byte ('\0')) the argument string s is printed, followed by a colon and a blank. Then the message and a new-line.

To be of most use, the argument string should include the name of the function that incurred the error. The error number is taken from the external variable errno, which is set when errors occur but not cleared when successful calls are made.

The global error list sys_errlist[] 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[].

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 in <errno.h> 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 library 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 to perror(), the value of errno should be saved.

CONFORMING TO

The function perror() and the external errno (see errno(3)) conform to C89, C99, 4.3BSD, POSIX.1-2001. The externals sys_nerr and sys_errlist conform to BSD.

NOTES

The externals sys_nerr and sys_errlist are defined by glibc, but in <stdio.h>

SEE ALSO

err(3), errno(3), error(3), strerror(3)

COLOPHON

This page is part of release 3.24 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


  Copyright (c) 1994 Michael Haardt (michaelmoria.de), 1994-06-04
Copyright (c) 1995 Michael Haardt
     (michaelcantor.informatik.rwth-aachen.de), 1995-03-16
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'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, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
USA.

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)