How to modify the current position. whence
can be SEEK_SET, then offset is the absolute position
in the file (0 is the first byte), SEEK_CUR then the
position will change by offset (ie. -5 means to move
5 bytes to the beginning of the file) or SEEK_END.
SEEK_END means that the offset is relative to the
end of the file (-1 is the last byte and 0 is
the EOF).
RESULT
0 on success and -1 on error. If an error occurred, the global
variable errno is set.