Re: C precedence - relative comparisons before equality operators

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c
Subject	Re: C precedence - relative comparisons before equality operators
Date	2021-09-06 09:09 +0200
Organization	A noiseless patient Spider
Message-ID	<sh4eqr$98j$1@dont-email.me> (permalink)
References	<sh2vvh$oir$1@dont-email.me> <87h7eylr24.fsf@bsb.me.uk>

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On 05/09/2021 22:12, Ben Bacarisse wrote:
> James Harris <james.harris.1@gmail.com> writes:
> 
>> According to
>>
>>   https://en.cppreference.com/w/c/language/operator_precedence
>>
>> and other references C applies relative comparisons (<, <=, >=, >)
>> before equality comparisons (==, !=) rather than giving them all the
>> same priority.
>>
>> Anyone know why the precedences were designed that way?
>>
>> Are there certain idioms in which that arrangement is useful?
> 
> I'm curious now too.  I don't know of any, but then I've not see a
> particularly large quantity of C code.
> 
> There is one that uses arithmetic between comparisons to get a -1, 0, +1
> result where such a thing is required:
> 
>   (a >= b) - (b >= a)
> 
> but that, of course, /needs/ the parentheses.
> 
> As to why it's like this, I suspect that DMR just liked lots of
> precedence levels to avoid ()s in as many cases as possible.  If you do
> decide to separate the groups, one has to be higher than the other and,
> though not common or idiomatic, equality and non-equality of comparisons
> seem to make more sense than comparisons of equality and non-equality.
> 

The relational operators and equality operators can be applied to
different things (there are more possibilities for equality comparison).
 I guess that meant it made sense to consider them as separate operator
groups.  And since each group has to fit at a different spot in the list
of precedences, it was either relational operators before equality
operators, or vice versa.

Thread

C precedence - relative comparisons before equality operators James Harris <james.harris.1@gmail.com> - 2021-09-05 18:49 +0100
  Re: C precedence - relative comparisons before equality operators Siri Cruise <chine.bleu@yahoo.com> - 2021-09-05 13:11 -0700
  Re: C precedence - relative comparisons before equality operators Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-09-05 21:12 +0100
    Re: C precedence - relative comparisons before equality operators David Brown <david.brown@hesbynett.no> - 2021-09-06 09:09 +0200
  Re: C precedence - relative comparisons before equality operators gazelle@shell.xmission.com (Kenny McCormack) - 2021-09-05 20:19 +0000
    Re: C precedence - relative comparisons before equality operators Richard Damon <Richard@Damon-Family.org> - 2021-09-05 17:52 -0400
      Re: C precedence - relative comparisons before equality operators Bart <bc@freeuk.com> - 2021-09-06 00:09 +0100
        Re: C precedence - relative comparisons before equality operators David Brown <david.brown@hesbynett.no> - 2021-09-06 09:15 +0200
          Re: C precedence - relative comparisons before equality operators Bart <bc@freeuk.com> - 2021-09-06 11:10 +0100
            Re: C precedence - relative comparisons before equality operators David Brown <david.brown@hesbynett.no> - 2021-09-06 13:01 +0200
              Re: C precedence - relative comparisons before equality operators Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-09-06 04:20 -0700
    Re: C precedence - relative comparisons before equality operators John Bode <jfbode1029@gmail.com> - 2021-09-07 09:27 -0500
      Re: C precedence - relative comparisons before equality operators Bart <bc@freeuk.com> - 2021-09-08 00:20 +0100
        Re: C precedence - relative comparisons before equality operators John Bode <jfbode1029@gmail.com> - 2021-09-08 14:18 -0500
  Re: C precedence - relative comparisons before equality operators Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-09-06 02:01 +0100
    Re: C precedence - relative comparisons before equality operators James Harris <james.harris.1@gmail.com> - 2021-09-06 09:39 +0100
      Re: C precedence - relative comparisons before equality operators Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-09-06 10:46 +0100
        Re: C precedence - relative comparisons before equality operators Richard Damon <Richard@Damon-Family.org> - 2021-09-06 10:09 -0400
          Re: C precedence - relative comparisons before equality operators Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-09-06 16:05 +0100
  Re: C precedence - relative comparisons before equality operators James Harris <james.harris.1@gmail.com> - 2021-09-06 09:27 +0100
    Re: C precedence - relative comparisons before equality operators James Harris <james.harris.1@gmail.com> - 2021-09-06 12:18 +0100
      Re: C precedence - relative comparisons before equality operators David Brown <david.brown@hesbynett.no> - 2021-09-06 13:44 +0200
        Re: C precedence - relative comparisons before equality operators James Harris <james.harris.1@gmail.com> - 2021-09-06 13:38 +0100
          Re: C precedence - relative comparisons before equality operators David Brown <david.brown@hesbynett.no> - 2021-09-06 18:12 +0200
        Re: C precedence - relative comparisons before equality operators tth <tth@none.invalid> - 2021-09-06 18:20 +0200
          Re: C precedence - relative comparisons before equality operators David Brown <david.brown@hesbynett.no> - 2021-09-06 23:40 +0200
      Re: C precedence - relative comparisons before equality operators Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-06 17:20 -0700
    Re: C precedence - relative comparisons before equality operators Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-09-06 13:44 +0100
    Re: C precedence - relative comparisons before equality operators Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-06 17:23 -0700
  Re: C precedence - relative comparisons before equality operators James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-06 23:07 -0400

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