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Re: C99: 7.18.1.1 Exact-width integer types

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On 1/26/22 19:24, Meredith Montgomery wrote:
> --8<---------------cut here---------------start------------->8---
> 7.18.1.1 Exact-width integer types
>
> 1. The typedef name intN_t designates a signed integer type with width
> N, no padding bits, and a two's complement representation. Thus,
> int8_t denotes a signed integer type with a width of exactly 8 bits.
> --8<---------------cut here---------------end--------------->8---
>
> It seems C99 garantees that these nice integers types will use two's
> complement. But I guess we have no such guarantee for int or char?
> It's only for intN_t. Can you share your experience on this? Thank
> you!

You're correct. The size-named types are likely to be typedefs for
standard types, but they're not required to be - they could be typedefs
for extended integer types. Keep in mind that the exact-sized types are
all optional. The only size-named types that are mandatory are the least
and fast versions, and only for 8, 16, 32, and 64 bits.
Since C2011, you can test for this: _Generic() checks for compatible
types, so you find _Generic() accepting 'int' as a match for 'int32_t',
you'll know that it meets those requirements too.

You can have a fully conforming implementation of C on almost any
platform, as a matter of deliberate design, and one of the key things
that makes that true are the things like this that aren't mandatory.

As a practical matter you're seldom going to run into non- two's
complement platforms, which is why C++ has made it mandatory, and why C
may be heading in the same direction.

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C99: 7.18.1.1 Exact-width integer types Meredith Montgomery <mmontgomery@levado.to> - 2022-01-26 21:24 -0300
  Re: C99: 7.18.1.1 Exact-width integer types Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-26 16:48 -0800
    Re: C99: 7.18.1.1 Exact-width integer types Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-26 17:02 -0800
  Re: C99: 7.18.1.1 Exact-width integer types James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-01-26 21:32 -0500
  Re: C99: 7.18.1.1 Exact-width integer types David Brown <david.brown@hesbynett.no> - 2022-01-27 09:14 +0100

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