From: michael@kjorling.se (Michael Kjörling)
Subject: [TUHS] When was #if introduced in C? (was: Re: Mac OS X is Unix)
Date: Tue, 3 Jan 2017 21:33:31 +0000 [thread overview]
Message-ID: <20170103213331.GN31772@yeono.kjorling.se> (raw)
In-Reply-To: <CANV78LQLKO03sCPVUe-EbiJonL-kgPQn1x+pm=FN3WWRZ7xLvg@mail.gmail.com>
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On 3 Jan 2017 13:05 -0800, from charles.unix.pro at gmail.com (Charles Anthony):
> I was compiling on a 32 bit int machine; the compiler flagged the '1u <<
> 60' as a fatal error due to the size of the shift -- on this compiler the
> expression evaluator was running before the dead code remover.
That was my thought too; the only way to guarantee that the code is
removed before the compiler sees it is to do so through the
preprocessor, thus #ifdef.
Of course, #ifdef is rather limited. The #if preprocessor directive is
more generic, but still significantly less versatile than the if()
language keyword.
Which makes me curious... Does anyone here happen to know when #if was
introduced in C? I suspect #ifdef came earlier simply by virtue of
being (at least to a naiive first approximation) far easier to
implement, as all that would be required would be to look at the macro
expansion table (already required by #define) and see if that
particular name had previously been #defined, as opposed to actually
evaluating an expression.
--
Michael Kjörling • https://michael.kjorling.se • michael at kjorling.se
“People who think they know everything really annoy
those of us who know we don’t.” (Bjarne Stroustrup)
next prev parent reply other threads:[~2017-01-03 21:33 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-03 20:19 [TUHS] Mac OS X is Unix Doug McIlroy
2017-01-03 21:05 ` Charles Anthony
2017-01-03 21:33 ` Michael Kjörling [this message]
2017-01-03 21:53 ` [TUHS] When was #if introduced in C? (was: Re: Mac OS X is Unix) Robert Swierczek
2017-01-03 21:57 ` Clem Cole
2017-01-03 21:56 ` Clem Cole
2017-01-03 21:35 ` [TUHS] Mac OS X is Unix Clem Cole
2017-01-03 22:10 ` Lyndon Nerenberg
2017-01-03 21:39 ` Lyndon Nerenberg
2017-01-03 22:12 ` ron minnich
2017-01-03 23:39 ` Tim Bradshaw
2017-01-04 0:12 ` ron minnich
2017-01-04 9:11 ` Tim Bradshaw
2017-01-04 10:04 ` Álvaro Jurado
2017-01-04 0:13 ` Steve Johnson
2017-01-04 3:50 ` Dan Cross
2017-01-04 12:26 ` Tim Bradshaw
2017-01-04 13:49 ` Random832
2017-01-04 15:02 ` Dan Cross
2017-01-04 17:14 ` tfb
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