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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Is this code considered to transgress the signed overflow purism?
Date: Sun, 30 Apr 2017 12:41:35 -0700
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Tim Rentsch <txr@alumni.caltech.edu> writes:
[...]
> For use in pre-processor conditionals, generally <limits.h> is
> needed, because (a) sizeof doesn't work in #if etc, and (b)
> even if it did, the sizes of types are potentially different in
> the pre-processor than they are in the program.

I'm not sure how meaningful your point (b) is.  *If* the preprocessor
were modified to permit sizeof, then it would be reasonable to
require that for example sizeof (long) must reflect the size of
type long on the target system.  In fact, I'd say it would be
unreasonable not to require that.  (In reality, the preprocessor
treats integer expressions as if they were of type intmax_t or
uintmax_t.  N1570 6.10.1p4.)

That reminds me of a discussion on comp.std.c back in 1998.  The
relevant quotation:

| > You are right.  It was nice back in the days when things like
| > 
| > #if (sizeof(int) == 8)
| > 
| > actually worked (on some compilers).
| 
| Must have been before my time.
| 
|      Dennis

Yes, the poster was Dennis Ritchie.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"