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

    Format

      #include  <wchar.h>

      int vfwprintf  (FILE *stream, const wchar_t *format, va_list

                     ap);

1 - Arguments

 stream

    A file pointer.

 format

    A pointer to a wide-character string containing the format
    specifications.

 ap

    A variable list of the items needed for output.

2 - Description

    The vfwprintf function is equivalent to the fwprintf 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) from <stdarg.h>.

    If the stream pointed to by stream has no orientation, vfwprintf
    makes the stream wide-oriented.

    See also fwprintf.

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.

4 - Examples

      The following example shows the use of the vfwprintf function
      in a general error reporting routine:

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

         void error(char *function_name, wchar_t *format,  . . . );
         {
            va_list args;

            va_start(args, format);
            /* print out name of function causing error */
            fwprintf(stderr, L"ERROR in %s: ", function_name);
            /* print out remainder of message */
            vfwprintf(stderr, format, args);
            va_end(args);
         }