This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       A call to fwide() with mode set to zero can be used to determine the current orientation of a stream.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                         FWIDE(3POSIX)

       The  functionality  described  on  this  reference  page is aligned with the ISO C standard. Any conflict
       between the requirements described  here  and  the  ISO C  standard  is  unintentional.  This  volume  of
       POSIX.1‐2017 defers to the ISO C standard.

       The  fwide()  function  shall  determine  the orientation of the stream pointed to by stream.  If mode is
       greater than zero, the function first attempts to make the stream wide-oriented. If  mode  is  less  than
       zero,  the  function  first  attempts  to  make the stream byte-oriented. Otherwise, mode is zero and the
       function does not alter the orientation of the stream.

       If the orientation of the stream has already been determined, fwide() shall not change it.

       The fwide() function shall not change the setting of errno if successful.

       Since no return value is reserved to indicate an  error,  an  application  wishing  to  check  for  error
       situations  should  set errno to 0, then call fwide(), then check errno, and if it is non-zero, assume an
       error has occurred.

       The fwide() function may fail if:

       EBADF  The stream argument is not a valid stream.

       Thefollowingsectionsareinformative.

       None.

       None.

       fwide — set stream orientation

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

       None.

       The fwide() function shall return a value greater than zero if, after the  call,  the  stream  has  wide-
       orientation,  a  value  less  than  zero if the stream has byte-orientation, or zero if the stream has no
       orientation.

       The Base Definitions volume of POSIX.1‐2017, <stdio.h>, <wchar.h>

       #include <stdio.h>
       #include <wchar.h>

       int fwide(FILE *stream, int mode);