Originální popis anglicky:
lseek - reposition read/write file offset
Návod, kniha: Linux Programmer's Manual
#include <sys/types.h>
#include <unistd.h>
off_t lseek(int fildes, off_t offset, int
whence);
The
lseek function repositions the offset of 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
existing end-of-file 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 return bytes of zeros (until data is actually written into the gap).
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.
- 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.
- EOVERFLOW
- The resulting file offset cannot be represented in an
off_t.
- ESPIPE
- fildes is associated with a pipe, socket, or
FIFO.
SVr4, POSIX, BSD 4.3
Some devices are incapable of seeking and POSIX does not specify which devices
must support it.
Linux specific restrictions: using
lseek on a tty device returns
ESPIPE.
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.
dup(2),
fork(2),
open(2),
fseek(3)
