va_list used in <stdio.h>

[Norbert Schlenker]

In article <10739 at smoke.BRL.MIL> gwyn at brl.arpa (Doug Gwyn) writes:
>In article <2095 at dataio.Data-IO.COM> bright at dataio.Data-IO.COM (Walter Bright) writes:
>-1. In stdio.h, include the lines:
>-	#ifndef __STDARG_H		/* #define'd by stdarg.h	*/
>-	#include <stdarg.h>		/* get definition of va_list	*/
>-	#endif
>
>No, don't do this.  <stdio.h> is not allowed to define the va_* macros.

What is <stdio.h> allowed to define?  It has to pick up <stddef.h>, because
the prototypes in <stdio.h> use size_t.  What makes <stddef.h> allowable
and <stdarg.h> forbidden?