|LSEEK(2)||System Calls Manual||LSEEK(2)|
lseek — reposition
read/write file offset
lseek() 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:
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.
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.
Upon successful completion,
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.
lseek() will fail and the file pointer
will remain unchanged if:
lseek() function conforms to
IEEE Std 1003.1-2008 (“POSIX.1”).
seek() system call first appeared in
Version 1 AT&T UNIX. In
Version 7 AT&T UNIX it was renamed to
lseek() for “long seek” due to a
larger offset argument type.
This document's use of whence is incorrect English, but is maintained for historical reasons.
|September 10, 2015||OpenBSD-current|