LSEEK(2) BSD System Calls Manual LSEEK(2)NAME
lseek -- reposition read/write file offset
SYNOPSIS
#include <unistd.h>
off_t
lseek(int fildes, off_t offset, int whence);
DESCRIPTION
The lseek() function repositions the offset of the file descriptor fildes to the argument offset according to the directive whence. The argu-
ment fildes must be an open file descriptor. Lseek() repositions the file pointer fildes as follows:
If whence is SEEK_SET, the offset is set to offset bytes.
If whence is SEEK_CUR, the offset is set to its current location plus offset bytes.
If whence is 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. 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).
Some devices are incapable of seeking. The value of the pointer associated with such a device is undefined.
RETURN VALUES
Upon successful completion, lseek() returns the resulting offset location as measured in bytes from the beginning of the file. Otherwise, a
value of -1 is returned and errno is set to indicate the error.
ERRORS
Lseek() will fail and the file pointer will remain unchanged if:
[EBADF] Fildes is not an open file descriptor.
[ESPIPE] Fildes is associated with a pipe, socket, or FIFO.
[EINVAL] Whence is not a proper value.
SEE ALSO dup(2), open(2)BUGS
This document's use of whence is incorrect English, but is maintained for historical reasons.
STANDARDS
The lseek() function conforms to IEEE Std 1003.1-1988 (``POSIX.1'').
4th Berkeley Distribution April 19, 1994 4th Berkeley Distribution
Check Out this Related Man Page
LSEEK(2) System Calls Manual LSEEK(2)NAME
lseek - move read/write pointer
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
#define SEEK_SET 0 /* offset is absolute */
#define SEEK_CUR 1 /* relative to current position */
#define SEEK_END 2 /* relative to end of file */
off_t lseek(int d, off_t offset, int whence)
DESCRIPTION
The descriptor d refers to a file or device open for reading and/or writing. Lseek sets the file pointer of d as follows:
If whence is SEEK_SET, the pointer is set to offset bytes.
If whence is SEEK_CUR, the pointer is set to its current location plus offset.
If whence is SEEK_END, the pointer is set to the size of the file plus offset.
Upon successful completion, the resulting pointer location as measured in bytes from beginning of the file is returned. Some devices are
incapable of seeking. The value of the pointer associated with such a device is undefined.
NOTES
Seeking far beyond the end of a file, then writing, creates a gap or "hole", which occupies no physical space and reads as zeros.
RETURN VALUE
Upon successful completion, the current file pointer value is returned. Otherwise, a value of -1 is returned and errno is set to indicate
the error.
ERRORS
Lseek will fail and the file pointer will remain unchanged if:
[EBADF] Fildes is not an open file descriptor.
[ESPIPE] Fildes is associated with a pipe or a socket.
[EINVAL] Whence is not a proper value.
SEE ALSO fcntl(2), open(2).
BUGS
This document's use of whence is incorrect English, but maintained for historical reasons.
4th Berkeley Distribution February 24, 1986 LSEEK(2)
I know there is lseek() function that will allow to write or read from certain position in the file. Is there similar function that will let do same but for array rather then file? (9 Replies)
Hi everybody,
i've been googling for ages now and gotten kinda desperate... The question, however, might be rather trivial for the experts: What is it exactly, i.e. physically, the POSIX function (for a file) "lseek" does? Does it trigger some kind of synchronization on disk? Is it just for the... (4 Replies)
I tried to use lseek system call to determine the number of bytes in a file. To do so, I used open system call with O_APPEND flag to open a file. As lseek returns the current offset so I called lseek for opened file with offset as zero and whence as SEEK_CUR. So I guess it must return the number of... (3 Replies)