Upon successful completion, the fgetwc function returns the wide-
    character code read from the file pointed to by file_ptr and
    converted to type wint_t. If the file is at end-of-file, the
    end-of-file indicator is set, and WEOF is returned. If an I/O
    read error occurred, then the error indicator is set, and WEOF is
    returned.

    Applications can use ferror or feof to distinguish between an
    error condition and an end-of-file condition.