`va_dcl' macro question

[Doug Gwyn]

In article <991 at ubu.warwick.UUCP> geoff at emerald.UUCP (Geoff Rimmer) writes:
>All I know about variable arguments in ANSI C is how to do prototypes,
>and define the functions.  However, I don't know how to read each of
>the arguments passed to the function.  Could someone email/post a
>simple function that will take a variable number of strings, and then
>print them to stdout one at a time.
>i.e.
>	void print_strings (char *str, ...)
>	{
>	...
>	}

Well, there has to be some way to tell when the argument list is
exhausted, which you didn't specify.  Let's assume that a null pointer
marks the end of the list.  Then here is how I would implement this:

#include	<stdio.h>
#if __STDC__
#include	<stdarg.h>
#else
#include	<varargs.h>
#define	const	/* nothing */
#endif

#if __STDC__
void					/* DESIGN BOTCH: should return status */
print_strings( register const char *str, ... )
#else
void
print_strings( va_alist )
	va_dcl
#endif
	{
#if !__STDC__
	register const char	*str;
#endif
	va_list		ap;

#if __STDC__
	va_start( ap, str );
#else
	va_start( ap );
	str = va_arg( ap, const char * );
#endif
	for ( ; str != NULL; str = va_arg( ap, const char * ) )
		(void)fputs( str, stdout );

	va_end( ap );
	}