Writes output to the stream under control of the wide-character
    format string.

    Format

      #include  <wchar.h>

      int vswprintf  (wchar_t *s, size_t n, const wchar_t *format,
                     va_list ap);

1  –  Arguments

 s

    A pointer to a multibyte character sequence.

 n

    The maximum number of bytes that comprise the multibyte
    character.

 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

    A variable list of the items needed for output.

2  –  Description

    The vswprintf function is equivalent to the swprintf 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.

    See also swprintf.

3  –  Return Values

    n                  The number of wide characters written.
    Negative value     Indicates an error. The function sets errno to
                       one of the following:

                       o  EILSEQ - Invalid character detected.

                       o  EINVAL - Insufficient arguments.

                       o  ENOMEM - Not enough memory available for
                          conversion.

                       o  ERANGE - Floating-point calculations
                          overflow.

                       o  EVMSERR - Nontranslatable OpenVMS error.
                          vaxc$errno contains the OpenVMS error code.
                          This might indicate that conversion to a
                          numeric value failed because of overflow.

                       The function can also set errno to the
                       following as a result of errors returned from
                       the I/O subsystem:

                       o  EBADF - The file descriptor is not valid.

                       o  EIO - I/O error.

                       o  ENOSPC - No free space on the device
                          containing the file.

                       o  ENXIO - Device does not exist.

                       o  EPIPE - Broken pipe.

                       o  ESPIPE - Illegal seek in a file opened for
                          append.

                       o  EVMSERR - Nontranslatable OpenVMS error.
                          vaxc$errno contains the OpenVMS error code.
                          This indicates that an I/O error occurred
                          for which there is no equivalent C error
                          code.