LSEEK(2)LSEEK(2)NAMElseek - move read/write pointer
BSD SYNOPSIS
#include <sys/file.h>
#define L_SET 0 /* set the seek pointer */
#define L_INCR 1 /* increment the seek pointer */
#define L_XTND 2 /* extend the file size */
off_t lseek(int fd, off_t offset, int whence);
POSIX SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
#define SEEK_SET 0 /* set the seek pointer */
#define SEEK_CUR 1 /* increment the seek pointer */
#define SEEK_END 2 /* extend the file size */
off_t lseek(int fd, off_t offset, int whence);
DESCRIPTION
The descriptor fd refers to a file or device open for reading and/or
writing. The lseek function sets the file pointer of fd as follows:
(1) If whence is L_SET (SEEK_SET for POSIX applications), the offset
is set to offset bytes.
(2) If whence is L_INCR (SEEK_CUR for POSIX applications), the offset
is set to its current value plus offset bytes.
(3) If whence is L_XTND (SEEK_END for POSIX applications), the offset
is set to the size of the file plus offset bytes.
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.
Seeking far beyond the end of a file, then writing, creates a gap or
“hole”, which occupies no physical space and reads as zeros. The lseek
function does not, by itself, extend the size of the file.
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
The lseek function will fail and the file pointer will remain unchanged
if:
[EBADF] fd is not an open file descriptor.
[ESPIPE] fd is associated with a pipe or a socket.
[EINVAL] whence is not a proper value, or the resulting file
offset is less than 0.
SEE ALSOcreat(2), dup(2), fcntl(2), open(2), read(2), sigaction(2P), write(2)
August 1, 1992 LSEEK(2)
