The lseek function repositions the offset of the file descriptor
fildes to the argument offset according to the directive
whence as follows:
The offset is set to offset bytes.
The offset is set to its current location plus
The offset is set to the size of the file plus
The lseek function allows the file offset to be set beyond the end of the
existing end-of-file of the file (but this does not change the size 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).
Upon successful completion, lseek returns the resulting offset location
as measured in bytes from the beginning of the file. Otherwise, a value of
(off_t)-1 is returned and errno is set to indicate the error.
This document's use of whence is incorrect English, but maintained for
When converting old code, substitute values for whence with the following
SVR1-3 returns long instead of off_t, BSD returns int.
Note that file descriptors created by dup(2) or fork(2) share the
current file position pointer, so seeking on such files may be subject to race