[apple/xnu.git] / bsd / man / man2 / lseek.2

.\"	$NetBSD: lseek.2,v 1.6 1995/02/27 12:34:09 cgd Exp $
.\"
.\" Copyright (c) 1980, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)lseek.2	8.3 (Berkeley) 4/19/94
.\"
.Dd April 19, 1994
.Dt LSEEK 2
.Os BSD 4
.Sh NAME
.Nm lseek
.Nd reposition read/write file offset
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft off_t
.Fo lseek
.Fa "int fildes"
.Fa "off_t offset"
.Fa "int whence"
.Fc
.Sh DESCRIPTION
The
.Fn lseek
function repositions the offset of the file descriptor
.Fa fildes
to the
argument
.Fa offset ,
according to the directive
.Fa whence .
The argument
.Fa fildes
must be an open
file descriptor.
.Fn Lseek
repositions the file pointer
.Fa fildes
as follows:
.Bl -item -offset indent
.It
If
.Fa whence
is
.Dv SEEK_SET ,
the offset is set to
.Fa offset
bytes.
.It
If
.Fa whence
is
.Dv SEEK_CUR ,
the offset is set to its current location plus
.Fa offset
bytes.
.It
If
.Fa whence
is
.Dv SEEK_END ,
the offset is set to the size of the
file plus
.Fa offset
bytes.
.El
.Pp
The
.Fn lseek
function allows the file offset to be set beyond the end
of the existing end-of-file of the file. If data is later written
at this point, subsequent reads of the data in the gap return
bytes of zeros (until data is actually written into the gap).
.Pp
Some devices are incapable of seeking.  The value of the pointer
associated with such a device is undefined.
.Sh RETURN VALUES
Upon successful completion,
.Fn lseek
returns the resulting offset location as measured in bytes from the
beginning of the file.
Otherwise,
a value of -1 is returned and
.Va errno
is set to indicate
the error.
.Sh ERRORS
.Fn Lseek
will fail and the file pointer will remain unchanged if:
.Bl -tag -width Er
.\" ==========
.It Bq Er EBADF
.Em Fildes
is not an open file descriptor.
.\" ==========
.It Bq Er EINVAL
.Fa Whence
is not a proper value.
.\" ==========
.It Bq Er EINVAL
The seek location (calculated from
.Fa offset
and
.Fa whence )
is negative.
.\" ==========
.It Bq Er EOVERFLOW
The seek location is too large to be stored
in an object of type off_t.
.\" ==========
.It Bq Er ESPIPE
.Em Fildes
is associated with a pipe, socket, or FIFO.
.El
.Sh SEE ALSO
.Xr dup 2 ,
.Xr open 2
.Sh BUGS
This document's use of
.Fa whence
is incorrect English, but is maintained for historical reasons.
.Sh STANDARDS
The
.Fn lseek
function conforms to 
.St -p1003.1-88 .
Commit	Line	Data
9bccf70c A	1	.\" $NetBSD: lseek.2,v 1.6 1995/02/27 12:34:09 cgd Exp $
	2	.\"
	3	.\" Copyright (c) 1980, 1991, 1993
	4	.\" The Regents of the University of California. All rights reserved.
	5	.\"
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
	14	.\" 3. All advertising materials mentioning features or use of this software
	15	.\" must display the following acknowledgement:
	16	.\" This product includes software developed by the University of
	17	.\" California, Berkeley and its contributors.
	18	.\" 4. Neither the name of the University nor the names of its contributors
	19	.\" may be used to endorse or promote products derived from this software
	20	.\" without specific prior written permission.
	21	.\"
	22	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	23	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	24	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	25	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	26	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	27	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	28	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	29	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	30	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	31	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	32	.\" SUCH DAMAGE.
	33	.\"
	34	.\" @(#)lseek.2 8.3 (Berkeley) 4/19/94
	35	.\"
	36	.Dd April 19, 1994
	37	.Dt LSEEK 2
	38	.Os BSD 4
	39	.Sh NAME
	40	.Nm lseek
	41	.Nd reposition read/write file offset
	42	.Sh SYNOPSIS
	43	.Fd #include <unistd.h>
	44	.Ft off_t
2d21ac55 A	45	.Fo lseek
	46	.Fa "int fildes"
	47	.Fa "off_t offset"
	48	.Fa "int whence"
	49	.Fc
9bccf70c A	50	.Sh DESCRIPTION
	51	The
	52	.Fn lseek
	53	function repositions the offset of the file descriptor
	54	.Fa fildes
	55	to the
	56	argument
2d21ac55	57	.Fa offset ,
9bccf70c	58	according to the directive
2d21ac55	59	.Fa whence .
9bccf70c A	60	The argument
	61	.Fa fildes
	62	must be an open
	63	file descriptor.
	64	.Fn Lseek
	65	repositions the file pointer
	66	.Fa fildes
	67	as follows:
	68	.Bl -item -offset indent
	69	.It
	70	If
	71	.Fa whence
	72	is
	73	.Dv SEEK_SET ,
	74	the offset is set to
	75	.Fa offset
	76	bytes.
	77	.It
	78	If
	79	.Fa whence
	80	is
	81	.Dv SEEK_CUR ,
	82	the offset is set to its current location plus
	83	.Fa offset
	84	bytes.
	85	.It
	86	If
	87	.Fa whence
	88	is
	89	.Dv SEEK_END ,
	90	the offset is set to the size of the
	91	file plus
	92	.Fa offset
	93	bytes.
	94	.El
	95	.Pp
	96	The
	97	.Fn lseek
	98	function allows the file offset to be set beyond the end
	99	of the existing end-of-file of the file. If data is later written
	100	at this point, subsequent reads of the data in the gap return
	101	bytes of zeros (until data is actually written into the gap).
	102	.Pp
	103	Some devices are incapable of seeking. The value of the pointer
	104	associated with such a device is undefined.
	105	.Sh RETURN VALUES
	106	Upon successful completion,
	107	.Fn lseek
	108	returns the resulting offset location as measured in bytes from the
	109	beginning of the file.
	110	Otherwise,
	111	a value of -1 is returned and
	112	.Va errno
	113	is set to indicate
	114	the error.
	115	.Sh ERRORS
	116	.Fn Lseek
	117	will fail and the file pointer will remain unchanged if:
	118	.Bl -tag -width Er
2d21ac55	119	.\" ==========
9bccf70c A	120	.It Bq Er EBADF
	121	.Em Fildes
	122	is not an open file descriptor.
2d21ac55	123	.\" ==========
9bccf70c A	124	.It Bq Er EINVAL
	125	.Fa Whence
	126	is not a proper value.
2d21ac55 A	127	.\" ==========
	128	.It Bq Er EINVAL
	129	The seek location (calculated from
	130	.Fa offset
	131	and
	132	.Fa whence )
	133	is negative.
	134	.\" ==========
	135	.It Bq Er EOVERFLOW
	136	The seek location is too large to be stored
	137	in an object of type off_t.
	138	.\" ==========
	139	.It Bq Er ESPIPE
	140	.Em Fildes
	141	is associated with a pipe, socket, or FIFO.
9bccf70c A	142	.El
	143	.Sh SEE ALSO
	144	.Xr dup 2 ,
	145	.Xr open 2
	146	.Sh BUGS
	147	This document's use of
	148	.Fa whence
	149	is incorrect English, but is maintained for historical reasons.
	150	.Sh STANDARDS
	151	The
	152	.Fn lseek
	153	function conforms to
	154	.St -p1003.1-88 .