1. I would like to see _BitInt(1) allowed in both C and C++.
The question is what to do in C++ if C does not change to allow it.
I'm not sure; probably for your proposal, I would follow the C rules.
Unless you think adding it to C++ would help to persuade C to allow it....
If C allows it, then I think C++ definitely should. But if C does not allow it, then I don't see that as being an argument as to why C++ should not.
Since C and C++ both mandate two's complement representation, if either language were to allow _BitInt(1), it would be capable of holding either 0 or -1. There is no risk of WG21 doing something here that will be incompatible with something that WG14 decides to do later.
2. I agree with your reasoning.
Regards,
Paul
-----Original message-----
From: Jan Schultke via Std-Proposals <std-proposals@lists.isocpp.org>
Sent: Monday, September 1 2025, 11:03 am
To: C++ Proposals <std-proposals@lists.isocpp.org>
Cc: Jan Schultke <janschultke@googlemail.com>
Subject: [std-proposals] D3666R0 Bit-precise integers
Hey,
As some of you may already know, I am working on bringing bit-precise
integers (_BitInt) to C++. See a very early draft of the paper here:
https://isocpp.org/files/papers/D3666r0.html
The debate over whether _BitInt should be a fundamental type or
library type has been largely settled, however there are two other
contentious points:
1. C does not allow _BitInt(1); should C++ to make generic programming
more comfortable?
2. Should the _BitInt keyword exist in C++? I currently propose to
have it, mainly because it inevitably will exist as a compiler
extension or compatibility macro, and it seems pointlessly
user-hostile not to just standardize existing practice.
If you have some early feedback, especially feedback on these two
points, that would be appreciated.
You should expect the finished paper to be in the September mailing.
Jan
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