Undefined behavior
The fsetpos function is called to set a position that was not returned by a previous
successful call to the fgetpos function on a stream associated with the same file
(7.19.9.3).
Undefined behavior
The fsetpos function is called to set a position that was not returned by a previous
successful call to the fgetpos function on a stream associated with the same file
(7.19.9.3).