Name
lseek — reposition read/write file offset
Synopsis
off_t
lseek( |
int |
fildes, |
| |
off_t |
offset, |
| |
int |
whence); |
DESCRIPTION
The lseek() function
repositions the offset of the open file associated with the
file descriptor fildes to the argument
offset according to
the directive whence
as follows:
SEEK_SET-
The offset is set to offset bytes.
SEEK_CUR-
The offset is set to its current location plus
offset
bytes.
SEEK_END-
The offset is set to the size of the file plus
offset
bytes.
The lseek() function allows
the file offset to be set beyond the end of the file (but
this does not change the size of the file). If data is later
written at this point, subsequent reads of the data in the
gap (a "hole") return null bytes ('\0') until data is
actually written into the gap.
RETURN VALUE
Upon successful completion, lseek() returns the resulting offset
location as measured in bytes from the beginning of the file.
Otherwise, a value of (off_t)−1 is returned
and errno is set to indicate the
error.
ERRORS
- EBADF
-
fildes is
not an open file descriptor.
- EINVAL
-
whence is
not one of SEEK_SET, SEEK_CUR, SEEK_END; or the
resulting file offset would be negative, or beyond the
end of a seekable device.
- EOVERFLOW
-
The resulting file offset cannot be represented in
an off_t.
- ESPIPE
-
fildes is
associated with a pipe, socket, or FIFO.
CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001.
NOTES
This document's use of whence is incorrect English,
but maintained for historical reasons.
Some devices are incapable of seeking and POSIX does not
specify which devices must support lseek().
On Linux, using lseek() on a
tty device returns ESPIPE.
When converting old code, substitute values for whence with the following
macros:
SVr1-3 returns long instead of off_t, BSD returns int.
Note that file descriptors created by dup(2) or fork(2) share the current
file position pointer, so seeking on such files may be
subject to race conditions.
SEE ALSO
dup(2), fork(2), open(2), fseek(3), lseek64(3), posix_fallocate(3)
t
Copyright (c) 1980, 1991 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
6.5 (Berkeley) 3/10/91
Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu>
Modified 1995-06-10 by Andries Brouwer <aeb@cwi.nl>
Modified 1996-10-31 by Eric S. Raymond <esr@thyrsus.com>
Modified 1998-01-17 by Michael Haardt
<michael@cantor.informatik.rwth-aachen.de>
Modified 2001-09-24 by Michael Haardt <michael@moria.de>
Modified 2003-08-21 by Andries Brouwer <aeb@cwi.nl>
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