fwide man page


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.

fwide — set stream orientation


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

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. 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.

Return Value

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 fwide() function may fail if:

The stream argument is not a valid stream.

The following sections are informative.

Application Usage

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

See Also

The Base Definitions volume of POSIX.1‐2008, <stdio.h>, <wchar.h>