Path: utzoo!utgpu!water!watmath!clyde!rutgers!rochester!ur-tut!sunybcs!boulder!hao!noao!mcdsun!sunburn!gtx!al
From: al@gtx.com (0732)
Newsgroups: comp.lang.c
Subject: Re: C sintax
Message-ID: <548@gtx.com>
Date: 28 Jan 88 16:40:31 GMT
References: <7072@brl-smoke.ARPA> <7160@brl-smoke.ARPA> <3932@hoptoad.uucp> <4079@june.cs.washington.edu> <4080@june.cs.washington.edu>
Reply-To: al@gtx.UUCP (Al Filipski)
Organization: GTX Corporation, Phoenix
Lines: 41

In article <4080@june.cs.washington.edu> pardo@uw-june.UUCP (David Keppel) writes:
->>What, precisely, does x+=*a+++*b mean?
->
->Well, actually it is ambiguous.  There are 2 (or more?) ways to parse
->it.  I'm not sure the behavior is defined from lexer to lexer as to
->which one is preferred.  Here are some possible interpretations:
->
->    tmp = *a + ++*b;	/* means increment *b and add that to *a */
->    x += tmp;
->    switch (x) {...}
->
->the (an) other is
->
->    tmp = *a++ + *b;	/* means add *a to *b and increment a */
->    x += tmp;
->    switch (x) {...}
->
->Not, of course that this is the most obfuscated code possible, but
->it does get the point across.

Actually, it is not ambiguous.  RTFK&R. The issue is whether x+++y means
(x++)+y or x+(++y). According to K&R, p 179, the answer can only
be (x++)+y.  The rule is "the next token is taken to include  the longest
string of characters which could possibly constitute a token."  I think
there is an implicit assumption of left-to-right parsing.

Notice that this makes 1+++b syntactically illegal, even though it might
reasonably be interpreted as 1+(++b).

I'll stick my neck out and say I don't think there ARE any syntactic
ambiguities in C. (there are, of course, the semantic ones resulting
from undefined order of evaluation).  The potential ambiguities such
as the dangling else and those involving the comma operator are solved
by fiat.

Are there any syntactic ambiguities K&R didn't resolve?

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