[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
.Fn lseek "int fildes" "off_t offset" "int whence"
.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 ESPIPE
.Em Fildes
is associated with a pipe, socket, or FIFO.
.It Bq Er EINVAL
.Fa Whence
is not a proper value.
.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
	45	.Fn lseek "int fildes" "off_t offset" "int whence"
	46	.Sh DESCRIPTION
	47	The
	48	.Fn lseek
	49	function repositions the offset of the file descriptor
	50	.Fa fildes
	51	to the
	52	argument
	53	.Fa offset
	54	according to the directive
	55	.Fa whence.
	56	The argument
	57	.Fa fildes
	58	must be an open
	59	file descriptor.
	60	.Fn Lseek
	61	repositions the file pointer
	62	.Fa fildes
	63	as follows:
	64	.Bl -item -offset indent
65	.It
66	If
67	.Fa whence
68	is
69	.Dv SEEK_SET ,
70	the offset is set to
71	.Fa offset
72	bytes.
73	.It
74	If
75	.Fa whence
76	is
77	.Dv SEEK_CUR ,
78	the offset is set to its current location plus
79	.Fa offset
80	bytes.
81	.It
82	If
83	.Fa whence
84	is
85	.Dv SEEK_END ,
86	the offset is set to the size of the
87	file plus
88	.Fa offset
89	bytes.
90	.El
91	.Pp
92	The
93	.Fn lseek
94	function allows the file offset to be set beyond the end
95	of the existing end-of-file of the file. If data is later written
96	at this point, subsequent reads of the data in the gap return
97	bytes of zeros (until data is actually written into the gap).
98	.Pp
99	Some devices are incapable of seeking. The value of the pointer
100	associated with such a device is undefined.
101	.Sh RETURN VALUES
102	Upon successful completion,
103	.Fn lseek
104	returns the resulting offset location as measured in bytes from the
105	beginning of the file.
106	Otherwise,
107	a value of -1 is returned and
108	.Va errno
109	is set to indicate
110	the error.
111	.Sh ERRORS
112	.Fn Lseek
113	will fail and the file pointer will remain unchanged if:
114	.Bl -tag -width Er
115	.It Bq Er EBADF
116	.Em Fildes
117	is not an open file descriptor.
118	.It Bq Er ESPIPE
119	.Em Fildes
120	is associated with a pipe, socket, or FIFO.
121	.It Bq Er EINVAL
122	.Fa Whence
123	is not a proper value.
124	.El
125	.Sh SEE ALSO
126	.Xr dup 2 ,
127	.Xr open 2
128	.Sh BUGS
129	This document's use of
130	.Fa whence
131	is incorrect English, but is maintained for historical reasons.
132	.Sh STANDARDS
133	The
134	.Fn lseek
135	function conforms to
136	.St -p1003.1-88 .