Description

   The fwide function determines the orientation of the stream
   pointed to by stream and sets the orientation of a nonoriented
   stream according to the mode argument in the following way:

   If the mode
   argument is:     Then the fwide function:

   greater than     makes the stream wide-oriented.
   zero
   less than zero   makes the stream byte-oriented.
   zero             does not alter the orientation of the stream.

   If the orientation of the stream has already been set, fwide does
   not alter it. Because no error status is defined for fwide, the
   calling application should check errno if fwide returns a 0.