参数里只有省略号参数该怎么获得参数列表

    int my_debug_printf(const char* str, ...)
    {
        int t = -1;

        //debug_begin();

        va_list list;

        va_start(list, str);

        t = vprintf(str, list);

        va_end(list);

        return t;
    }

// variable_argument_lists.cpp
#include <stdio.h>
#include <stdarg.h>

//  Declaration, but not definition, of ShowVar.
void ShowVar( char *szTypes, ... );
int main() {
   ShowVar( "fcsi", 32.4f, 'a', "Test string", 4 );
}

//  ShowVar takes a format string of the form
//   "ifcs", where each character specifies the
//   type of the argument in that position.
//
//  i = int
//  f = float
//  c = char
//  s = string (char *)
//
//  Following the format specification is a list
//  of n arguments, where n == strlen( szTypes ).
void ShowVar( char *szTypes, ... ) {
   va_list vl;
   int i;

   //  szTypes is the last argument specified; all
   //   others must be accessed using the variable-
   //   argument macros.
   va_start( vl, szTypes );

   // Step through the list.
   for( i = 0; szTypes[i] != '\0'; ++i ) {
      union Printable_t {
         int     i;
         float   f;
         char    c;
         char   *s;
      } Printable;

      switch( szTypes[i] ) {   // Type to expect.
         case 'i':
            Printable.i = va_arg( vl, int );
            printf_s( "%i\n", Printable.i );
         break;

         case 'f':
             Printable.f = va_arg( vl, double );
             printf_s( "%f\n", Printable.f );
         break;

         case 'c':
             Printable.c = va_arg( vl, char );
             printf_s( "%c\n", Printable.c );
         break;

         case 's':
             Printable.s = va_arg( vl, char * );
             printf_s( "%s\n", Printable.s );
         break;

         default:
         break;
      }
   }
   va_end( vl );
}