From 2198625575165869088 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,f53a695f204bf879 X-Google-Attributes: gidf78e5,public From: wmm@fastdial.net Subject: Re: Alternative tokens and token pasting Date: 2000/07/18 Message-ID: <8kvj7m$4pg$1@nnrp1.deja.com>#1/1 X-Deja-AN: 647433136 Approved: Fergus Henderson , moderator of comp.std.c++ References: X-Authentication-Warning: backdraft.briar.org: smap set sender to using -f X-Http-User-Agent: Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt) X-Complaints-To: abuse@demon.net X-Mail2News-Path: news.demon.net!mulga.cs.mu.oz.au X-Trace: mail2news.demon.co.uk 963859747 mail2news:21371 mail2news mail2news.demon.co.uk X-Http-Proxy: 1.1 x55.deja.com:80 (Squid/1.1.22) for client 205.181.152.41 Organization: Deja.com - Before you buy. X-Article-Creation-Date: Mon Jul 17 18:28:30 2000 GMT X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-MyDeja-Info: XMYDJUIDwmmj16 Newsgroups: comp.std.c++ In article , Martin von Loewis wrote: > What is the meaning of an alternative token (2.5) when occuring in > token pasting (16.3.3)? Consider > > #define paste(a,b) a##b > > paste(m,xor) > paste(xor,=) > > Which of these has well-defined behaviour (if any), and what is that > behaviour? Which is ill-formed with required diagnostic (if any)? The alternative tokens are preprocessing tokens (they're preprocessing-op-or-punc, according to 2.12p1, which makes them preprocessing tokens, according to 2.4). 16.3.3p3 says that the preprocessing token preceding ## is concatenated with the preprocessing token following the ##, and that "If the result is not a value preprocessing token, the behavior is undefined." I'd take that to mean that the value of "paste(m,xor)" is the identifier "mxor", and that "paste(xor,=)" has undefined behavior. -- William M. Miller, wmm@fastdial.net Vignette Corporation (www.vignette.com) Sent via Deja.com http://www.deja.com/ Before you buy. --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://reality.sgi.com/austern_mti/std-c++/faq.html ]