不好意思，简单问题，两年前用过现在忘了，急(50分)

兄弟底子不扎实
请问，c下面动态参数(...)（个数和类型不定）是怎么样定义的，记得是有一个专门的ARG之类的，
但最近没用了，实在很没印象了

也就是说我要实现一个形如printf(,...)类的函数，要怎样做？
~~~

急

来自MSDN的例子：
/* VA.C: The program below illustrates passing a variable
* number of arguments using the following macros:
* va_start va_arg va_end
* va_list va_dcl (UNIX only)
*/

#include <stdio.h>
#define ANSI /* Comment out for UNIX version */
#ifdef ANSI /* ANSI compatible version */
#include <stdarg.h>
int average( int first, ... );
#else /* UNIX compatible version */
#include <varargs.h>
int average( va_list );
#endif

void main( void )
{
/* Call with 3 integers (-1 is used as terminator). */
printf( "Average is: %d/n", average( 2, 3, 4, -1 ) );

/* Call with 4 integers. */
printf( "Average is: %d/n", average( 5, 7, 9, 11, -1 ) );

/* Call with just -1 terminator. */
printf( "Average is: %d/n", average( -1 ) );
}

/* Returns the average of a variable list of integers. */
#ifdef ANSI /* ANSI compatible version */
int average( int first, ... )
{
int count = 0, sum = 0, i = first;
va_list marker;

va_start( marker, first ); /* Initialize variable arguments. */
while( i != -1 )
{
sum += i;
count++;
i = va_arg( marker, int);
}
va_end( marker ); /* Reset variable arguments. */
return( sum ? (sum / count) : 0 );
}
#else /* UNIX compatible version must use old-style definition. */
int average( va_alist )
va_dcl
{
int i, count, sum;
va_list marker;

va_start( marker ); /* Initialize variable arguments. */
for( sum = count = 0; (i = va_arg( marker, int)) != -1; count++ )
sum += i;
va_end( marker ); /* Reset variable arguments. */
return( sum ? (sum / count) : 0 );
}
#endif


Output

Average is: 3
Average is: 8
Average is: 0

是这样的。
不用试也知道