145 lines
3.9 KiB
Groff
145 lines
3.9 KiB
Groff
.\" 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
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd April 19, 1994
|
|
.Dt LSEEK 2
|
|
.Os BSD 4
|
|
.Sh NAME
|
|
.Nm lseek
|
|
.Nd reposition read/write file offset
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.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 position pointer associated with the file
|
|
descriptor
|
|
.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 position 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 call is expected to conform to
|
|
.St -p1003.1-90 .
|
|
.Sh HISTORY
|
|
A
|
|
.Fn lseek
|
|
function call appeared in
|
|
.At v7 .
|