Writes output to an array of wide characters under control of the
    wide-character format string.

    Format

      #include  <wchar.h>

      int vwprintf  (const wchar_t *format, va_list ap);

1  –  Arguments

 format

    A pointer to a wide-character string containing the format
    specifications. For more information about format and conversion
    specifications and their corresponding arguments, see the
    "Understanding Input and Output" chapter of the VSI C RTL
    Reference Manual.

 ap

    The variable list of items needed for output.

2  –  Description

    The vwprintf function is equivalent to the wprintf function,
    with the variable argument list replaced by the ap argument.
    Initialize ap with the va_start macro, and possibly with
    subsequent va_arg calls. The vwprintf function does not invoke
    the va_end macro.

    See also wprintf.

3  –  Return Values

    x                  The number of wide characters written, not
                       counting the terminating null wide character.
    Negative value     Indicates an error. Either n or more wide
                       characters were requested to be written, or a
                       conversion error occurred, in which case errno
                       is set to EILSEQ.