From owner-freebsd-standards  Sat Oct 12 13:21:31 2002
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Date: Sat, 12 Oct 2002 13:20:03 -0700
From: Terry Lambert <tlambert2@mindspring.com>
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To: Tony Finch <dot@dotat.at>
Cc: Bruce Evans <bde@zeta.org.au>,
	Craig Rodrigues <rodrigc@attbi.com>, freebsd-standards@FreeBSD.ORG,
	freebsd-hackers@FreeBSD.ORG
Subject: Re: Problem detecting POSIX symbolic constants
References: <20021012171803.F15910-100000@gamplex.bde.org> <3DA7E0F4.5988CA77@mindspring.com> <20021012151336.A24868@chiark.greenend.org.uk>
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Tony Finch wrote:
> > With just an "&" or an "|", you actually need a much less complicated
> > state machine to evaluate a constant expression.  With the "||"/"&&",
> > you almost have to do an edge associative operation, which implies a
> > much more complex state machine for the preprocessor, I think.
> 
> No -- the short-circuiting behaviour of && and || only matters if
> you can have side-effects, which you can't in the preprocessor,
> so there is no need to implement it (unifdef doesn't).

Consider:

#if _DEFINED_SUPPORTED  && defined(SOMETHING)

-- Terry

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