Path: utzoo!attcan!uunet!husc6!bu-cs!mirror!ima!haddock!karl
From: karl@haddock.ima.isc.com (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: passing variable numbers of arguments
Keywords: varargs assert() nargs()
Message-ID: <11555@haddock.ima.isc.com>
Date: 26 Jan 89 23:41:15 GMT
References: <11378@haddock.ima.isc.com> <9321@smoke.BRL.MIL> <11410@haddock.ima.isc.com> <9358@smoke.BRL.MIL> <202@mstan.Morgan.COM> <9381@smoke.BRL.MIL> <11428@haddock.ima.isc.com> <203@s5.Morgan.COM>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 22

In article <203@s5.Morgan.COM> dff@Morgan.COM (Daniel F. Fisher) writes:
>In article <11428@haddock.ima.isc.com> karl@haddock.ima.isc.com (Karl Heuer)
>[suggests that for most purposes] a boolean va_isarg() would suffice.
>
>I considered [that], but concluded that it is not appropriate, since the
>unavailability of a necessary argument represents a programming error which
>is best treated as an assertion failure.

Here's a counterexample.
	int min(int first, ...) {
	    int i;  va_list ap;
	    va_start(ap, first);
	    while (va_isarg(ap)) {
	        if ((i = va_arg(ap, int)) < first) first = i;
	    }
	    return (first);
	}

This function, which cannot be written in either pre-ANSI or ANSI C, uses
va_isarg() to obviate the need for an explicit extra argument.

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint