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LSEEK(2) Linux Programmer's Manual LSEEK(2)
NAME
lseek - reposition read/write file offset
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
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 mea-
sured 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.
RESTRICTIONS
Some devices are incapable of seeking and POSIX does not specify which devices must
support lseek().
Linux specific restrictions: using lseek() on a tty device returns ESPIPE.
NOTES
This document's use of whence is incorrect English, but maintained for historical
reasons.
When converting old code, substitute values for whence with the following macros:
old new
0 SEEK_SET
1 SEEK_CUR
2 SEEK_END
L_SET SEEK_SET
L_INCR SEEK_CUR
L_XTND SEEK_END
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)
Linux 2001-09-24 LSEEK(2)
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On Apache/2.2.3 (Red Hat)
Under GNU General Public License
2009-11-10 08:13 @127.0.0.1 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)