off_t
lseek(
int fildes
, off_t offset
, int whence
)
)
function repositions the offset of the file descriptor
fildes
to the
argument
offset
according to the directive
whence
.
The argument
fildes
must be an open
file descriptor.
lseek(
)
repositions the file pointer
fildes
as follows:
whence
is
SEEK_SET
,
the offset is set to
offset
bytes.
whence
is
SEEK_CUR
,
the offset is set to its current location plus
offset
bytes.
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.
)
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.
)
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, or the resulting file offset would be invalid.
)
function conforms to
ISO/IEC 9945-1:1990 (``POSIX.1'') .
whence
is incorrect English, but is maintained for historical reasons.