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From: brian@anorak.coverform.lan (Brian Somers)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Compiler bug?
Date: 10 Nov 1996 01:33:54 -0000
Organization: Coverform Ltd.
Lines: 41
Sender: brian@awfulhak.demon.co.uk
Message-ID: <563be2$i7b@anorak.coverform.lan>
References: <55p7ck$r2l@csgrad.cs.vt.edu>
<55qdup$8jv@sol.ctr.columbia.edu>
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In article <55qdup$8jv@sol.ctr.columbia.edu>,
wpaul@ctr.columbia.edu (Bill Paul) writes:
: Daring to challenge the will of the almighty Leviam00se, Tommy Johnson
: (tjohnson@csgrad.cs.vt.edu) had the courage to say:
:
>: This program doesn't work as I think it should. On line 10, b is not
>: incremented between the first and second b++'s, though it is correct
>: after the entire expression.
[.....]
: [chop]
>: a=c[b++]|((c[b++])<<8);
: [chop]
:
: I believe you have invoked undefined compiler behavior with this code.
[.....]
: (No, I can't quote the exact part of the ANSI spec that says this code
: is bogus; I just know that it is.)
:
: You need to rewrite your code so that you do not have two b++'s in the
: same statement; then it should behave the same regardless of the platform
: or compiler. This should as you expect:
:
: a = c[b++];
: a |= ((c[b++])<<8);
[.....]
Yep - I agree completely.
The spec says that the variable will be incremented sometime after its
value is taken. It warns that "when" is undefined and says that code
such as
foo( x++, x++ )
will not port.
--
Brian <brian%anorak.coverform.lan@awfulhak.demon.co.uk>
<http://www.awfulhak.demon.co.uk/>
Don't _EVER_ lose your sense of humour....
.