.\"	$OpenBSD: strerror.3,v 1.16 2019/05/16 13:35:16 schwarze Exp $
.\"
.\" Copyright (c) 1980, 1991 Regents of the University of California.
.\" Copyright (c) 2017 Ingo Schwarze <schwarze@openbsd.org>
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" Processing Systems.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd $Mdocdate: May 16 2019 $
.Dt STRERROR 3
.Os
.Sh NAME
.Nm strerror ,
.Nm strerror_l ,
.Nm strerror_r
.Nd get error message string
.Sh SYNOPSIS
.In string.h
.Ft char *
.Fn strerror "int errnum"
.Ft char *
.Fn strerror_l "int errnum" "locale_t locale"
.Ft int
.Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen"
.Sh DESCRIPTION
These functions map the error number
.Fa errnum
to an error message string.
.Pp
.Fn strerror
and
.Fn strerror_l
return a string containing a maximum of
.Dv NL_TEXTMAX
characters, including the trailing NUL.
This string is not to be modified by the calling program.
The string returned by
.Fn strerror
may be overwritten by subsequent calls to
.Fn strerror
in any thread.
The string returned by
.Fn strerror_l
may be overwritten by subsequent calls to
.Fn strerror_l
in the same thread.
.Pp
.Fn strerror_r
is a thread safe version of
.Fn strerror
that places the error message in the specified buffer
.Fa strerrbuf .
.Pp
On
.Ox ,
the global locale, the thread-specific locale, and the
.Fa locale
argument are ignored.
.Sh RETURN VALUES
.Fn strerror
and
.Fn strerror_l
return a pointer to the error message string.
If an error occurs, the error code is stored in
.Va errno .
.Pp
.Fn strerror_r
returns zero upon successful completion.
If an error occurs, the error code is stored in
.Va errno
and the error code is returned.
.Sh ERRORS
All these functions may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
.Fa errnum
is not a valid error number.
The returned error string will consist of an error message that includes
.Fa errnum .
.El
.Pp
.Fn strerror_r
may also fail if:
.Bl -tag -width Er
.It Bq Er ERANGE
The error message is larger than
.Fa buflen
characters.
The message will be truncated to fit.
.El
.Sh SEE ALSO
.Xr intro 2 ,
.Xr newlocale 3 ,
.Xr perror 3 ,
.Xr setlocale 3
.Sh STANDARDS
The
.Fn strerror
function conforms to
.St -isoC-99 .
The
.Fn strerror_l
and
.Fn strerror_r
functions conform to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn strerror
function has been available since
.Bx 4.3 Reno ,
.Fn strerror_r
since
.Ox 3.3 ,
and
.Fn strerror_l
since
.Ox 6.2 .
.Sh CAVEATS
On systems other than
.Ox ,
the
.Dv LC_MESSAGES
.Xr locale 1
category can cause different strings to be returned instead of the
normal error messages; see CAVEATS in
.Xr setlocale 3
for details.