#include <stdio.h> #include <wchar.h> int fwide(FILE *stream, int mode);
The fwide() function determines the orientation of the stream pointed to by stream. If mode is greater than 0, the function first attempts to make the stream wide-orientated. If mode is less than 0, the function first attempts to make the stream byte-orientated. Otherwise, mode is 0 and the function does not alter the orientation of the stream.
If the orientation of the stream has already been determined, fwide() does not change it.
Because 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 returns a value greater than 0 if, after the call, the stream has wide-orientation, a value less than 0 if the stream has byte-orientation, or 0 if the stream has no orientation.
The fwide() function may fail if:
The stream argument is not a valid stream.
A call to fwide() with mode set to 0 can be used to determine the current orientation of a stream.
See attributes(5) for descriptions of the following attributes: