.\" Copyright (c) 1980, 1991 Regents of the University of California.
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.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" Processing Systems.
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.\"	$OpenBSD: strerror.3,v 1.11 2012/03/26 05:07:38 guenther Exp $
.\"
.Dd $Mdocdate: March 26 2012 $
.Dt STRERROR 3
.Os
.Sh NAME
.Nm strerror
.Nd get error message string
.Sh SYNOPSIS
.Fd #include <string.h>
.Ft char *
.Fn strerror "int errnum"
.Ft int
.Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen"
.Sh DESCRIPTION
The
.Fn strerror
and
.Fn strerror_r
functions map the error number
.Fa errnum
to a language-dependent error message string.
.Pp
.Fn strerror
returns 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,
but may be overwritten by subsequent calls to
.Fn strerror .
.Pp
.Fn strerror_r
is a thread safe version of
.Fn strerror
that places the error message in the specified buffer
.Fa strerrbuf .
.Sh RETURN VALUES
.Fn strerror
returns 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
.Fn strerror
and
.Fn strerror_r
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 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 perror 3 ,
.Xr setlocale 3
.Sh STANDARDS
The
.Fn strerror
function conforms to
.St -ansiC-99 .
The
.Fn strerror_r
function conforms to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn strerror
function first appeared in
.Bx 4.3 Reno .
The
.Fn strerror_r
function first appeared in
.Ox 3.3 .