Re: clarification about enums in C

From	Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups	comp.lang.c
Subject	Re: clarification about enums in C
Date	2020-02-26 23:03 +0000
Organization	A noiseless patient Spider
Message-ID	<875zftx86i.fsf@bsb.me.uk> (permalink)
References	<aaf0f57f-4ae1-4c4a-a0aa-314eade48440@googlegroups.com> <r35hab$ts9$1@dont-email.me> <5c585469-72c8-42f8-9e74-848f160db602@googlegroups.com>

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already5chosen@yahoo.com writes:

> On Wednesday, February 26, 2020 at 12:29:40 PM UTC+2, David Brown wrote:
<cut>
>> "A" and "B" are named integer constant values (much like 'a' and 'b').
>> So they have type "int".
>
> That' how language of the standard sounds.
> But it's not how gcc and clang work.
>
> enum enum_t {
>  uns = (unsigned)-1,

This violates a constraint.  Recent gcc and clang do indeed report it.

>  neg = -1,
> };
> Both in gcc and in clang uns has type 'unsigned int' rather than
> 'int'.

The program has undefined behaviour by this point.  gcc and clang and
making a good job of trying to work out what the program should
reasonably do.

> And indeed it differs from type of 'enum_t' which in ths case is 'int'.
>
> Microsoft's compiler (VS2015) is easier to understand and don't
> violate (my understanding of) Standard, but it is less flexible -
> everything, including uns, is 'int'.

What int value does VS2015 pick for uns?  I can see to plausible
choices, INT_MAX and -1.

<cut>
-- 
Ben.

Thread

clarification about enums in C Thiago Adams <thiago.adams@gmail.com> - 2020-02-25 15:38 -0800
  Re: clarification about enums in C luser droog <luser.droog@gmail.com> - 2020-02-25 19:19 -0800
  Re: clarification about enums in C James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-25 21:17 -0800
    Re: clarification about enums in C Thiago Adams <thiago.adams@gmail.com> - 2020-02-27 04:01 -0800
  Re: clarification about enums in C David Brown <david.brown@hesbynett.no> - 2020-02-26 11:29 +0100
    Re: clarification about enums in C already5chosen@yahoo.com - 2020-02-26 14:05 -0800
      Re: clarification about enums in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-02-26 23:03 +0000
        Re: clarification about enums in C already5chosen@yahoo.com - 2020-02-26 23:29 -0800
          Re: clarification about enums in C already5chosen@yahoo.com - 2020-02-27 01:42 -0800
            Re: clarification about enums in C David Brown <david.brown@hesbynett.no> - 2020-02-27 11:02 +0100
              Re: clarification about enums in C Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-02-27 06:37 -0800
                Re: clarification about enums in C David Brown <david.brown@hesbynett.no> - 2020-02-27 16:18 +0100
                Re: clarification about enums in C James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-27 23:24 -0500
      Re: clarification about enums in C David Brown <david.brown@hesbynett.no> - 2020-02-27 09:50 +0100
        Re: clarification about enums in C Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-02-27 06:33 -0800
          Re: clarification about enums in C already5chosen@yahoo.com - 2020-02-27 06:53 -0800
          Re: clarification about enums in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-02-27 15:05 +0000
          Re: clarification about enums in C David Brown <david.brown@hesbynett.no> - 2020-02-27 16:24 +0100
          Re: clarification about enums in C Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-02-28 01:27 -0800
      Re: clarification about enums in C already5chosen@yahoo.com - 2020-02-27 01:29 -0800
        Re: clarification about enums in C David Brown <david.brown@hesbynett.no> - 2020-02-27 11:12 +0100
          Re: clarification about enums in C already5chosen@yahoo.com - 2020-02-27 03:09 -0800
            Re: clarification about enums in C David Brown <david.brown@hesbynett.no> - 2020-02-27 14:33 +0100
              Re: clarification about enums in C already5chosen@yahoo.com - 2020-02-27 05:44 -0800
                Re: clarification about enums in C David Brown <david.brown@hesbynett.no> - 2020-02-27 14:57 +0100
        Re: clarification about enums in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-02-27 11:53 +0000
          Re: clarification about enums in C James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-27 23:52 -0500
            Re: clarification about enums in C Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-02-28 01:30 -0800
  Re: clarification about enums in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-02-26 14:09 +0000
    Re: clarification about enums in C Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-02-26 09:47 -0800
      Re: clarification about enums in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-02-26 21:04 +0000

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