strerror.3: Correct description of error return for XSI strerror_r()

[thirdparty/man-pages.git] / man3 / strerror.3

.\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright (C) 2005, Michael Kerrisk <mtk.manpages@gmail.com>
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.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 18:05:30 1993 by Rik Faith <faith@cs.unc.edu>
.\" Modified Fri Feb 16 14:25:17 1996 by Andries Brouwer <aeb@cwi.nl>
.\" Modified Sun Jul 21 20:55:44 1996 by Andries Brouwer <aeb@cwi.nl>
.\" 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  2012-04-22 "" "Linux Programmer's Manual"
.SH NAME
strerror, strerror_r \- return string describing error number
.SH SYNOPSIS
.nf
.B #include <string.h>
.sp
.BI "char *strerror(int " errnum );
.sp
.BI "int strerror_r(int " errnum ", char *" buf ", size_t " buflen );
            /* XSI-compliant */
.sp
.BI "char *strerror_r(int " errnum ", char *" buf ", size_t " buflen );
            /* GNU-specific */
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
The XSI-compliant version of
.BR strerror_r ()
is provided if:
.br
(_POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE\ >=\ 600) && !\ _GNU_SOURCE
.br
Otherwise, the GNU-specific version is provided.
.SH DESCRIPTION
The
.BR strerror ()
function returns a pointer to a string that describes the error
code passed in the argument \fIerrnum\fP, possibly using the
.B LC_MESSAGES
part of the current locale to select the appropriate language.
This string must not be modified by the application, but may be
modified by a subsequent call to
.BR perror (3)
or
.BR strerror ().
No library function will modify this string.

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),
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_SOURCE
is defined by default with the value
200112L, so that the XSI-compliant version of
.BR strerror_r ()
is provided by default.

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 buflen .

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 the string always includes a terminating null byte.
.SH "RETURN VALUE"
The
.BR strerror ()
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.

The XSI-compliant
.BR strerror_r ()
function returns 0 on success;
on error, a (positive) error number is returned.
.SH ERRORS
.TP
.B EINVAL
The value of
.I errnum
is not a valid error number.
.TP
.B ERANGE
Insufficient storage was supplied to contain the error description string.
.SH "CONFORMING TO"
.BR strerror ()
is specified by POSIX.1-2001, C89, C99.
.BR strerror_r ()
is specified by POSIX.1-2001.

The GNU-specific
.BR strerror_r ()
function is a nonstandard extension.

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.
.SH "SEE ALSO"
.BR err (3),
.BR errno (3),
.BR error (3),
.BR perror (3),
.BR strsignal (3)