FWIDE(3P) POSIX Programmer's Manual FWIDE(3P)PROLOG
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.
NAMEfwide — set stream orientation
int fwide(FILE *stream, int mode);
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.1‐2008
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. Other‐
wise, mode is zero and the function does not alter the orientation of
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 success‐
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
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 orienta‐
The fwide() function may fail if:
EBADF The stream argument is not a valid stream.
The following sections are informative.
A call to fwide() with mode set to zero can be used to determine the
current orientation of a stream.
The Base Definitions volume of POSIX.1‐2008, <stdio.h>, <wchar.h>
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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.ker‐
IEEE/The Open Group 2013 FWIDE(3P)