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Date: Fri, 17 Apr 2015 20:35:12 +0200
From: Szabolcs Nagy <>
Subject: Re: Explicit casts in ctype.h suppress compiler warnings

* Alexander Monakov <> [2015-04-17 21:24:09 +0300]:
> I confirm that the idea works, and as Rich said it causes a warning with
> -pedantic -std=c89 with gcc-4.5..4.7 (but not 4.8, 4.9).

i assume we could use compound literals in c89 with __extension__

> > Do you have an idea in mind for how we could achieve that? I suspect
> > the macros are still better optimizable than the inline function
> > approach, so I'd lean towards doing a macro that avoids evaluating c
> > and just checks its type, which would involve using ?: I think.
> I admit I was thinking of doing isspace-style inlines everywhere, but thanks
> to your suggestion I was able to come up with this:
> static __inline void __is_int(int a) {}
> #define isdigit(a) (__is_int(0?(a):0), ((unsigned)(a)-'0') < 10)

i think using :0 there is not useful because null
pointer constants are special in ?:

i think rich meant something like

#define isdigit(a) (((0?1U:(a))-'0') < 10)

which works when the conversion rank of a is <= unsigned

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