.\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)
+.\" and Copyright (C) 2005, 2014 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
+.\" %%%LICENSE_START(VERBATIM)
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
-.\"
+.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
-.\"
+.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
.\"
.\" References consulted:
.\" Linux libc source code
.\" Modified Mon Oct 15 21:16:25 2001 by John Levon <moz@compsoc.man.ac.uk>
.\" Modified Tue Oct 16 00:04:43 2001 by Andries Brouwer <aeb@cwi.nl>
.\" Modified Fri Jun 20 03:04:30 2003 by Andries Brouwer <aeb@cwi.nl>
+.\" 2005-12-13, mtk, Substantial rewrite of strerror_r() description
+.\" Addition of extra material on portability and standards.
.\"
-.TH STRERROR 3 2001-10-16 "" "Linux Programmer's Manual"
+.TH STRERROR 3 2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
-strerror, strerror_r \- return string describing error code
+strerror, strerror_r, strerror_l \- return string describing error number
.SH SYNOPSIS
.nf
.B #include <string.h>
-.sp
+.PP
.BI "char *strerror(int " errnum );
-.sp
-.B #define _XOPEN_SOURCE 600
-.B #include <string.h>
-.sp
-.BI "int strerror_r(int " errnum ", char *" buf ", size_t " n );
+.PP
+.BI "int strerror_r(int " errnum ", char *" buf ", size_t " buflen );
+ /* XSI-compliant */
+.PP
+.BI "char *strerror_r(int " errnum ", char *" buf ", size_t " buflen );
+ /* GNU-specific */
+.PP
+.BI "char *strerror_l(int " errnum ", locale_t " locale );
.fi
+.PP
+.in -4n
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.in
+.ad l
+.PP
+.BR strerror_r ():
+.RS 4
+The XSI-compliant version is provided if:
+.br
+(_POSIX_C_SOURCE\ >=\ 200112L) && ! \ _GNU_SOURCE
+.br
+Otherwise, the GNU-specific version is provided.
+.RE
+.ad
.SH DESCRIPTION
-The \fBstrerror()\fP function returns a string describing the error
-code passed in the argument \fIerrnum\fP, possibly using the LC_MESSAGES
+The
+.BR strerror ()
+function returns a pointer to a string that describes the error
+code passed in the argument
+.IR errnum ,
+possibly using the
+.B LC_MESSAGES
part of the current locale to select the appropriate language.
+(For example, if
+.I errnum
+is
+.BR EINVAL ,
+the returned description will be "Invalid argument".)
This string must not be modified by the application, but may be
-modified by a subsequent call to \fBperror()\fP or \fBstrerror()\fP.
-No library function will modify this string.
-
-The \fBstrerror_r()\fP function is similar to \fBstrerror()\fP, but is
-thread safe. It returns the string in the user-supplied buffer
+modified by a subsequent call to
+.BR strerror ()
+or
+.BR strerror_l ().
+No other library function, including
+.BR perror (3),
+will modify this string.
+.\"
+.SS strerror_r()
+The
+.BR strerror_r ()
+function is similar to
+.BR strerror (),
+but is
+thread safe.
+This function is available in two versions:
+an XSI-compliant version specified in POSIX.1-2001
+(available since glibc 2.3.4, but not POSIX-compliant until glibc 2.13),
+and a GNU-specific version (available since glibc 2.0).
+The XSI-compliant version is provided with the feature test macros
+settings shown in the SYNOPSIS;
+otherwise the GNU-specific version is provided.
+If no feature test macros are explicitly defined,
+then (since glibc 2.4)
+.B _POSIX_C_SOURCE
+is defined by default with the value
+200112L, so that the XSI-compliant version of
+.BR strerror_r ()
+is provided by default.
+.PP
+The XSI-compliant
+.BR strerror_r ()
+is preferred for portable applications.
+It returns the error string in the user-supplied buffer
.I buf
of length
-.IR n .
-
-.SH "RETURN VALUE"
-The \fBstrerror()\fP function returns the appropriate error description
-string, or an unknown error message if the error code is unknown.
-The value of \fIerrno\fP is not changed for a successful call, and is
-set to a non-zero value upon error.
-The \fBstrerror_r()\fP function returns 0 on success and \-1 on failure,
-setting \fIerrno\fP.
-
+.IR buflen .
+.PP
+The GNU-specific
+.BR strerror_r ()
+returns a pointer to a string containing the error message.
+This may be either a pointer to a string that the function stores in
+.IR buf ,
+or a pointer to some (immutable) static string
+(in which case
+.I buf
+is unused).
+If the function stores a string in
+.IR buf ,
+then at most
+.I buflen
+bytes are stored (the string may be truncated if
+.I buflen
+is too small and
+.I errnum
+is unknown).
+The string always includes a terminating null byte (\(aq\\0\(aq).
+.\"
+.SS strerror_l()
+.BR strerror_l ()
+is like
+.BR strerror (),
+but maps
+.I errnum
+to a locale-dependent error message in the locale specified by
+.IR locale .
+The behavior of
+.BR strerror_l ()
+is undefined if
+.I locale
+is the special locale object
+.BR LC_GLOBAL_LOCALE
+or is not a valid locale object handle.
+.SH RETURN VALUE
+The
+.BR strerror (),
+.BR strerror_l (),
+and the GNU-specific
+.BR strerror_r ()
+functions return
+the appropriate error description string,
+or an "Unknown error nnn" message if the error number is unknown.
+.PP
+The XSI-compliant
+.BR strerror_r ()
+function returns 0 on success.
+On error,
+a (positive) error number is returned (since glibc 2.13),
+or \-1 is returned and
+.I errno
+is set to indicate the error (glibc versions before 2.13).
+.PP
+POSIX.1-2001 and POSIX.1-2008 require that a successful call to
+.BR strerror ()
+or
+.BR strerror_l ()
+shall leave
+.I errno
+unchanged, and note that,
+since no function return value is reserved to indicate an error,
+an application that wishes to check for errors should initialize
+.I errno
+to zero before the call,
+and then check
+.I errno
+after the call.
.SH ERRORS
.TP
.B EINVAL
.TP
.B ERANGE
Insufficient storage was supplied to contain the error description string.
-
-.SH "CONFORMING TO"
-SVID 3, POSIX, BSD 4.3, ISO/IEC 9899:1990 (C89).
+.SH VERSIONS
+The
+.BR strerror_l ()
+function first appeared in glibc 2.6.
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbw14 lb lb
+l l l.
+Interface Attribute Value
+T{
+.BR strerror ()
+T} Thread safety MT-Unsafe race:strerror
+T{
+.BR strerror_r (),
.br
-.BR strerror_r()
-with prototype as given above is specified by SUSv3, and was in use
-under Digital Unix and HP Unix. An incompatible function, with prototype
-.sp
-.BI "char *strerror_r(int " errnum ", char *" buf ", size_t " n );
-.sp
-is a GNU extension used by glibc (since 2.0),
-and must be regarded as obsolete in view of SUSv3.
-The GNU version may, but need not, use the user-supplied buffer.
-If it does, the result may be truncated in case the supplied buffer
-is too small. The result is always NUL-terminated.
-.SH "SEE ALSO"
+.BR strerror_l ()
+T} Thread safety MT-Safe
+.TE
+.SH CONFORMING TO
+.BR strerror ()
+is specified by POSIX.1-2001, POSIX.1-2008, C89, and C99.
+.BR strerror_r ()
+is specified by POSIX.1-2001 and POSIX.1-2008.
+.\" FIXME . for later review when Issue 8 is one day released...
+.\" A future POSIX.1 may remove strerror_r()
+.\" http://austingroupbugs.net/tag_view_page.php?tag_id=8
+.\" http://austingroupbugs.net/view.php?id=508
+.PP
+.BR strerror_l ()
+is specified in POSIX.1-2008.
+.PP
+The GNU-specific
+.BR strerror_r ()
+function is a nonstandard extension.
+.PP
+POSIX.1-2001 permits
+.BR strerror ()
+to set
+.I errno
+if the call encounters an error, but does not specify what
+value should be returned as the function result in the event of an error.
+On some systems,
+.\" e.g., Solaris 8, HP-UX 11
+.BR strerror ()
+returns NULL if the error number is unknown.
+On other systems,
+.\" e.g., FreeBSD 5.4, Tru64 5.1B
+.BR strerror ()
+returns a string something like "Error nnn occurred" and sets
+.I errno
+to
+.B EINVAL
+if the error number is unknown.
+C99 and POSIX.1-2008 require the return value to be non-NULL.
+.SH NOTES
+The GNU C Library uses a buffer of 1024 characters for
+.BR strerror ().
+This buffer size therefore should be sufficient to avoid an
+.B ERANGE
+error when calling
+.BR strerror_r ()
+and
+.BR strerror_l ().
+.SH SEE ALSO
+.BR err (3),
.BR errno (3),
+.BR error (3),
.BR perror (3),
-.BR strsignal (3)
+.BR strsignal (3),
+.BR locale (7)
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