注意：不定长参数需要使用stdarg.h这个头文件。

#include <stdarg.h>

#include <stdio.h>

void outs(char *fmt, ...)
{
    static char tmp[80];
    va_list ap;

    sprintf(tmp, "%s\r\n", fmt);

    va_start(ap, fmt);

    vprintf(tmp, ap);

    va_end(ap);

};

void foo(char *fmt, ...)
{
     va_list ap;
     int d;
     char c, *p, *s;

     va_start(ap, fmt);
     while (*fmt)
          switch(*fmt++) {
          case 's':           /* string */
               s = va_arg(ap, char *);
               printf("string %s\n", s);
               break;
          case 'd':           /* int */
               d = va_arg(ap, int);
               printf("int %d\n", d);
               break;
          case 'c':           /* char */
               /* need a cast here since va_arg only
                  takes fully promoted types */
               c = (char) va_arg(ap, int);
               printf("char %c\n", c);
               break;
          }
     va_end(ap);
}

void main()

{

	outs("Hello, %s", username);

	foo("sdc", username, usercount, 'A');

};