Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!batcomputer!munnari.oz.au!metro!otc!grahamd
From: grahamd@otc.otca.oz.au (Graham Dumpleton)
Newsgroups: comp.lang.c
Subject: Expansion of macro arguments in ANSI cpp.
Message-ID: <2610@otc.otca.oz>
Date: 23 Apr 91 01:38:03 GMT
Sender: news@otc.otca.oz
Reply-To: grahamd@otc.otca.oz.au (Graham Dumpleton)
Organization: OTC Development Unit, Australia
Lines: 33


I checked the FAQ list but couldn't find this mentioned so:

What is an ANSI conforming C preprocessor mean't to do in the following
situation.

#define preone onepre
#define one two
#define addpre(arg) pre##arg

addpre(one)


The preprocessor on a RS6000 running AIX when run with the argument
'-qlanglvl=ansi' to invoke ANSI compatability produces

onepre

In other words it performs the join and then checks to see if the result
is a macro and if so expands it.

The pre-processor which we use though, which is based on the Decus cpp supplied
on the X tape produces the following

pretwo

In other words it has the effect of expanding the argument if it is a macro
first and then performing the join.

I tend to think that the Decus cpp is wrong but can someone please confirm this.

--
Graham Dumpleton (grahamd@otc.otca.oz.au)