Xref: utzoo comp.unix.wizards:5837 comp.lang.c:5764
Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!umd5!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.wizards,comp.lang.c
Subject: Re: (simple?) varargs question
Message-ID: <9917@mimsy.UUCP>
Date: 21 Dec 87 21:38:55 GMT
References: <10937@brl-adm.ARPA>
Followup-To: comp.lang.c
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 46

[Followups redirected to comp.lang.c]
In article <10937@brl-adm.ARPA> mrose@twg.arpa (Marshall Rose) writes:
>... I want to be able to do upto several levels of nesting of routines
>with variable arguments.  The hierarchy is like this:

[pretty picture deleted; pktlose calls saplose; xsprintf and saplose
both call asprintf]

>Each of these routines starts with a fixed number of arguments,
>followed by a format string and then a variable number of
>arguments.  Ultimately asprintf will call vsprintf or _doprnt to
>format a string.

All the intermediate functions need `variadic' forms.  It seems
to me best to write *all* varadic functions with both forms, thus:

	/* pktlose(int a, int b, const char *fmt, ...) */
	pktlose(va_alist)
		va_dcl
	{
		va_list l;

		/* va_start(fmt, l) */
		va_start(l);
		vpktlose(l);
		va_end(l);
	}

	/* vpktlose(va_list ap) */
	vpktlose(ap)
		va_list ap;
	{
		int a, b;

		a = va_arg(ap, int);
		b = va_arg(ap, int);
		...
		vsprintf(buffer, ap);
	}

Note that if you want to scan the `fmt' argument in
vpktlose, you are out of luck, since vsprintf needs it
too and there is no (portable) way to back up `ap'.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris