Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!uunet!mcsun!ukc!edcastle!aiai!aiai.ed.ac.uk!richard
From: richard@aiai.ed.ac.uk (Richard Tobin)
Newsgroups: comp.lang.c
Subject: Re: varargs -> varargs mystery
Message-ID: <4606@skye.ed.ac.uk>
Date: 3 May 91 14:34:23 GMT
References: <3099@cirrusl.UUCP> <1991May2.170148.12655@sparky.IMD.Sterling.COM>
Sender: news@aiai.ed.ac.uk
Reply-To: richard@aiai.uucp (Richard Tobin)
Organization: AIAI, University of Edinburgh, Scotland
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In article <1991May2.170148.12655@sparky.IMD.Sterling.COM> rick@sparky.IMD.Sterling.COM (Richard Ohnemus) writes:
>In article <3099@cirrusl.UUCP> Rahul Dhesi <dhesi@cirrus.COM> writes:
>>Suppose A is a varargs function, and it uses the first argument
>>supplied, and passes on the rest to B, which is also a varargs
>>function.  What is the right way to do it?

It can't be done.  What Rahul wants is the equivalent of Lisp's
"apply", and C doesn't have one.

>Just pass the variable argument list pointer instead of the address of 
>the pointer.

Note that he wanted to pass the arguments on to another varargs
function, not one that took a single va_list argument.

Imagine a function debug() which takes a "debugging level" and and
some arguments that will be passed on to fprintf() if the level is
high enough.  For this particular case C provides the functions
vfprintf() etc.  If there were a (portable) way to do what Rahul
wanted, those functions would be unnecessary.

-- Richard

Richard Tobin,                       JANET: R.Tobin@uk.ac.ed             
AI Applications Institute,           ARPA:  R.Tobin%uk.ac.ed@nsfnet-relay.ac.uk
Edinburgh University.                UUCP:  ...!ukc!ed.ac.uk!R.Tobin