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From: hansen@pegasus.att.com (Tony L. Hansen)
Newsgroups: comp.std.c
Subject: Re: <varargs.h> vs. function prototypes
Keywords: <varargs.h> usage
Message-ID: <1991Jun18.145823.2512@cbnewsk.att.com>
Date: 18 Jun 91 14:58:23 GMT
References: <25353@oolong.la.locus.com> <159364@pyramid.pyramid.com>
Sender: hansen@cbnewsk.att.com (tony.l.hansen)
Distribution: na
Organization: AT&T Bell Laboratories
Lines: 34

< From: markhall@pyrps5.pyramid.com (Mark Hall)
<	#ifdef __STDC__
<	void foo(char *format, ...)
<	#else
<	void foo(format, va_alist) char *format; va_dcl
<	#endif
<	{
<		va_list ap;
<		#ifdef __STDC__
<			va_start(ap,format);
<		#else
<			va_start(ap);
<		#endif
<		
<		[ ... rest of stuff the same ... ]
<	}

The above form for <varargs.h> usage is wrong. The documentation, and some
implementations, REQUIRE you to declare the function as:

	void foo(va_alist) va_dcl

and then pick off the fixed arguments using va_arg:

		char *format;

		format = va_arg(ap,char*);

Any other usage is non-portable (as portable as you can be using varargs.h,
that is.  :-) )

					Tony Hansen
			    hansen@pegasus.att.com, tony@attmail.com
				att!pegasus!hansen, attmail!tony