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Groups > comp.lang.c > #53891

Re: "lvalue"

From Keith Thompson <kst-u@mib.org>
Newsgroups comp.lang.c
Subject Re: "lvalue"
Date 2014-12-04 08:20 -0800
Organization None to speak of
Message-ID <lniohrpetm.fsf@nuthaus.mib.org> (permalink)
References (2 earlier) <m5nkqb$6qk$1@speranza.aioe.org> <m5nml1$gho$1@dont-email.me> <547F72A6.8030502@verizon.net> <lvalue-20141204013653@ram.dialup.fu-berlin.de> <m5oi1f$jmq$1@dont-email.me>

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James Kuyper <jameskuyper@verizon.net> writes:
> On 12/03/2014 07:38 PM, Stefan Ram wrote:
>> James Kuyper <jameskuyper@verizon.net> writes:
>>> Those two statements cannot both be true. The current standard is
>>> intended to identify *p as an lvalue, even if p has a null or
>>> indeterminate value, in which case *p does NOT refer to an object. C90's
>> 
>>   An attempt by me:
>> 
>>       �An expression is an /lvalue expression/,
>>       if it has the form
>> 
>>         v,
>> 
>>       where v is a variable or a parameter,
>
> It would be more consistent with the way the rest of the standard is
> written to say that "v is identifier that has been declared as
> designating an object" (compare with 6.5.1p2). That covers both of those
> cases.
>
>>       or if it has the form
>> 
>>         *E,
>> 
>>       where E is an expression of pointer type
>
> You need to be more specific - it should be a pointer to an object type,
> and it must point at an actual object (6.5.3.2p4)

What do you mean by "it must point to an actual object"?  If E is of
type int*, for example, then *E is an lvalue even if E is a null
pointer.  Actually that last part mixes source code and execution time
concepts.

[...]

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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Re: "lvalue" buja <buja66@gmail.com> - 2014-12-03 18:34 +0100
  Re: "lvalue" James Kuyper <jameskuyper@verizon.net> - 2014-12-03 13:03 -0500
  Re: "lvalue" jacob navia <jacob@spamsink.net> - 2014-12-03 19:29 +0100
    Re: "lvalue" buja <buja66@gmail.com> - 2014-12-03 20:01 +0100
      Re: "lvalue" Keith Thompson <kst-u@mib.org> - 2014-12-03 12:18 -0800
      Re: "lvalue" Geoff <geoff@invalid.invalid> - 2014-12-03 12:20 -0800
      Re: "lvalue" James Kuyper <jameskuyper@verizon.net> - 2014-12-03 15:29 -0500
        Re: "lvalue" James Kuyper <jameskuyper@verizon.net> - 2014-12-03 21:48 -0500
          Re: "lvalue" Keith Thompson <kst-u@mib.org> - 2014-12-04 08:20 -0800
            Re: "lvalue" James Kuyper <jameskuyper@verizon.net> - 2014-12-04 11:44 -0500
              Re: "lvalue" Keith Thompson <kst-u@mib.org> - 2014-12-04 11:41 -0800
                Re: "lvalue" James Kuyper <jameskuyper@verizon.net> - 2014-12-04 14:50 -0500
        Re: "lvalue" Keith Thompson <kst-u@mib.org> - 2014-12-03 23:40 -0800
    Re: "lvalue" Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-05 09:16 -0800

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