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.\" Copyright (c) 1994 Michael Haardt (michael@moria.de), Sat Jun 4 20:38:26 MET DST 1994
.\" Copyright (c) 1995 Michael Haardt (michael@cantor.informatik.rwth-aachen.de), Thu Mar 16 18:46:23 MET 1995
.\" Copyright (c) 1996 Andries Brouwer (aeb@cwi.nl), Sat Jan 13 00:16:41 MET 1996
.\"
.\" 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.
.\"
.\" Sat Jan 13 00:16:41 MET 1996, aeb: merged in some text contributed
.\" by Melvin Smith (msmith@falcon.mercer.peachnet.edu) and various
.\" other changes.
.\" Modified Fri May 16 23:41:15 1996 by Martin Schulze (joey@infodrom.north.de)
.\"
.TH PERROR 3 "May 16 1996" "" "Library functions"
.SH NAME
perror \- print a system error message
.SH SYNOPSIS
.B #include <stdio.h>
.sp
.BI "void perror(const char " *s );
.sp
.B #include <errno.h>
.sp
.BI "const char *" sys_errlist [];
.br
.BI "int " sys_nerr ;
.SH DESCRIPTION
The routine
.B perror()
produces a message on the standard error output, describing the last
error encountered during a call to a system or library function. The
argument string
.I s
is printed first, then 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
.IR errno ,
which is set when errors occur but not
cleared when non-erroneous calls are made.
The global error list
.IR sys_errlist "[]"
indexed by
.I errno
can be used to obtain the error message without the newline.
The largest message number provided in the table is
.IR sys_nerr " \-1."
Be careful when directly accessing this list because new error values
may not have been added to
.IR sys_errlist "[]."
When a system call fails, it usually returns \-1 and sets the
variable
.I errno
to a value describing what went wrong. (These values can be found in
.IR "<errno.h>" .)
Many library functions do likewise.
The function
.B perror()
serves to translate this error code into human-readable form.
Note that
.I 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
.BR perror ,
the value of
.I errno
should be saved.
.SH "CONFORMING TO"
ANSI C, BSD 4.3, POSIX, X/OPEN
.SH "SEE ALSO"
.BR strerror (3)
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