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Re: clarification about enums in C

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David Brown <david.brown@hesbynett.no> writes:
[...]
>> enum enum_t {
>>  uns = (unsigned)-1,
>>  neg = -1,
>> };
>> Both in gcc and in clang uns has type 'unsigned int' rather than 'int'.
>> And indeed it differs from type of 'enum_t' which in ths case is 'int'.
>
> This is an extension that these tools support - as do many compilers.
> If you want to ensure that you stick to standards-only code, use
> "-Wpedantic" (along with your choice of -std=c11, -std=c99 or -std=c90),
> and pay attention to the warnings.  The C standard does not say how
> "uns" should be treated, gcc's extensions do the "obvious" thing.

Ah, but gcc doesn't print a diagnostic with "-std=c11 -Wpedantic", even
though the code violates a constraint.

N1570 6.7.2.2p2:

    The expression that defines the value of an enumeration constant
    shall be an integer constant expression that has a value
    representable as an int.

Even my copy of gcc built from source that calls itself
    gcc (GCC) 10.0.0 20200111 (experimental)
fails to diagnose it.

A recent version of clang does print a diagnostic.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */

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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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