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	1	.\" Copyright (c) 1980, 1991, 1993
	2	.\" The Regents of the University of California. All rights reserved.
	3	.\"
	4	.\" This code is derived from software contributed to Berkeley by
	5	.\" the American National Standards Committee X3, on Information
	6	.\" Processing Systems.
	7	.\"
	8	.\" Redistribution and use in source and binary forms, with or without
	9	.\" modification, are permitted provided that the following conditions
	10	.\" are met:
	11	.\" 1. Redistributions of source code must retain the above copyright
	12	.\" notice, this list of conditions and the following disclaimer.
	13	.\" 2. Redistributions in binary form must reproduce the above copyright
	14	.\" notice, this list of conditions and the following disclaimer in the
	15	.\" documentation and/or other materials provided with the distribution.
	16	.\" 3. All advertising materials mentioning features or use of this software
	17	.\" must display the following acknowledgement:
	18	.\" This product includes software developed by the University of
	19	.\" California, Berkeley and its contributors.
	20	.\" 4. Neither the name of the University nor the names of its contributors
	21	.\" may be used to endorse or promote products derived from this software
	22	.\" without specific prior written permission.
	23	.\"
	24	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	25	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	26	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	27	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	28	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	29	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	30	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	31	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	32	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	33	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	34	.\" SUCH DAMAGE.
	35	.\"
	36	.\" @(#)strerror.3 8.1 (Berkeley) 6/9/93
	37	.\" $FreeBSD: src/lib/libc/string/strerror.3,v 1.23 2004/10/12 14:52:52 keramida Exp $
	38	.\"
	39	.Dd October 12, 2004
	40	.Dt STRERROR 3
	41	.Os
	42	.Sh NAME
	43	.Nm perror ,
	44	.Nm strerror ,
	45	.Nm strerror_r ,
	46	.Nm sys_errlist ,
	47	.Nm sys_nerr
	48	.Nd system error messages
	49	.Sh LIBRARY
	50	.Lb libc
	51	.Sh SYNOPSIS
	52	.In stdio.h
	53	.Ft void
	54	.Fn perror "const char *string"
	55	.Vt extern const char * const sys_errlist[] ;
	56	.Vt extern const int sys_nerr ;
	57	.In string.h
	58	.Ft "char *"
	59	.Fn strerror "int errnum"
	60	.Ft int
	61	.Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen"
	62	.Sh DESCRIPTION
	63	The
	64	.Fn strerror ,
	65	.Fn strerror_r
	66	and
	67	.Fn perror
	68	functions look up the error message string corresponding to an
	69	error number.
	70	.Pp
	71	The
	72	.Fn strerror
	73	function accepts an error number argument
	74	.Fa errnum
	75	and returns a pointer to the corresponding
	76	message string.
	77	.Pp
	78	The
	79	.Fn strerror_r
	80	function renders the same result into
	81	.Fa strerrbuf
	82	for a maximum of
	83	.Fa buflen
	84	characters and returns 0 upon success.
	85	.Pp
	86	The
	87	.Fn perror
	88	function finds the error message corresponding to the current
	89	value of the global variable
	90	.Va errno
	91	.Pq Xr intro 2
	92	and writes it, followed by a newline, to the
	93	standard error file descriptor.
	94	If the argument
	95	.Fa string
	96	is
	97	.Pf non- Dv NULL
	98	and does not point to the null character,
	99	this string is prepended to the message
	100	string and separated from it by
	101	a colon and space
	102	.Pq Dq Li ":\ " ;
	103	otherwise, only the error message string is printed.
	104	.Pp
	105	If the error number is not recognized, these functions return an error message
	106	string containing
	107	.Dq Li "Unknown error:\ "
	108	followed by the error number in decimal.
	109	The
	110	.Fn strerror
	111	and
	112	.Fn strerror_r
	113	functions return
	114	.Er EINVAL
	115	as a warning.
	116	Error numbers recognized by this implementation fall in
	117	the range 0 <
	118	.Fa errnum
	119	<
	120	.Fa sys_nerr .
	121	.Pp
	122	If insufficient storage is provided in
	123	.Fa strerrbuf
	124	(as specified in
	125	.Fa buflen )
	126	to contain the error string,
	127	.Fn strerror_r
	128	returns
	129	.Er ERANGE
	130	and
	131	.Fa strerrbuf
	132	will contain an error message that has been truncated and
	133	.Dv NUL
	134	terminated to fit the length specified by
	135	.Fa buflen .
	136	.Pp
	137	The message strings can be accessed directly using the external
	138	array
	139	.Va sys_errlist .
	140	The external value
	141	.Va sys_nerr
	142	contains a count of the messages in
	143	.Va sys_errlist .
	144	The use of these variables is deprecated;
	145	.Fn strerror
	146	or
	147	.Fn strerror_r
	148	should be used instead.
	149	.Sh SEE ALSO
	150	.Xr intro 2 ,
	151	.Xr psignal 3
	152	.Sh STANDARDS
	153	The
	154	.Fn perror
	155	and
	156	.Fn strerror
	157	functions conform to
	158	.St -isoC-99 .
	159	The
	160	.Fn strerror_r
	161	function conforms to
	162	.St -p1003.1-2001 .
	163	.Sh HISTORY
	164	The
	165	.Fn strerror
	166	and
	167	.Fn perror
	168	functions first appeared in
	169	.Bx 4.4 .
	170	The
	171	.Fn strerror_r
	172	function was implemented in
	173	.Fx 4.4
	174	by
	175	.An Wes Peters Aq wes@FreeBSD.org .
	176	.Sh BUGS
	177	For unknown error numbers, the
	178	.Fn strerror
	179	function will return its result in a static buffer which
	180	may be overwritten by subsequent calls.
	181	.Pp
	182	The return type for
	183	.Fn strerror
	184	is missing a type-qualifier; it should actually be
	185	.Vt const char * .
	186	.Pp
	187	Programs that use the deprecated
	188	.Va sys_errlist
	189	variable often fail to compile because they declare it
	190	inconsistently.