.\"	$OpenBSD: strerror.3,v 1.15 2017/09/05 03:16:13 schwarze Exp $
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.Dd $Mdocdate: September 5 2017 $
.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 ENVIRONMENT
On other operating systems, the behaviour of
.Fn strerror
and
.Fn strerror_r
may depend on the
.Dv LC_MESSAGES
.Xr locale 1 .
.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 .