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 fol-
lows:
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.