Path: news.eternal-september.org!eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Ben Bacarisse <ben@bsb.me.uk>
Newsgroups: comp.lang.c
Subject: Re: Top 10 most common hard skills listed on resumes...
Date: Wed, 11 Sep 2024 01:02:24 +0100
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Bart <bc@freeuk.com> writes:

> On 10/09/2024 15:15, Ben Bacarisse wrote:
>> Bart <bc@freeuk.com> writes:
>> 
>>> On 08/09/2024 17:44, Bart wrote:
>>>> On 08/09/2024 16:39, Ben Bacarisse wrote:
>>>>> Bart <bc@freeuk.com> writes:
>>>>>
>>>>>> In language like C, the LHS of an assignment is one of four categories:
>>>>>>
>>>>>>     A = Y;         // name
>>>>>>     *X = Y;        // pointer
>>>>>>     X[i] = Y;      // index
>>>>>>     X.m = Y;       // member select
>>>>>
>>>>> I can think of three others.  There may be more.
>>>> OK, so what are they?
>>>
>>> TM:
>>>> Yes, very good.  I count four or five, depending on what
>>> differences count as different.
>>>
>>> I guess nobody is going to say what those extra categories are, are
>>> they?
>> Sorry, I was busy.  I see KT as given a good summary (though I was not
>> counting forms in parentheses).
>> 
>>> It's bad form to call somebody out on something but then refuse to tell
>>> them exactly what they've got wrong or have missed out.
>>>
>>> 3, 4, or maybe 5 mysterious categories of LHS assignment terms that I have
>>> never been encountered in a million lines of C code I've processed, but
>>> nobody is willing to say what they are?
>>>
>>> I sense a wind-up.
>> You have implemented a C compiler.  The wind-up I sensed was your giving
>> out misinformation, but I'll just have to take your word for it that
>> you've been arguing about assignments without know what constitutes an
>> lvalue expression.
>> But when I didn't answer soon enough, surely you could have just looked
>> in any good C reference to find all the expression forms that are
>> lvalues.
>> 
>>>>> I can think of at least one expression form for X that contradicts this
>>>>> claim.
>>>> Example?
>>>
>>> Nothing here either.
>> f().m where f returns a struct.
>
> f().m is allowed with mcc and tcc compilers (but it doesn't do anything
> useful). It's not classed as an lvalue by gcc.

gcc is correct.  It isn't a lvalue.

> By "the LHS of an assignment", and "X is a term of any complexity" I imply
> those X's forming valid LHS terms.
>
> An X used as X[i]=Y, *X=Y, or X.m=Y, or even any of the Y's, could be
> rejected for lots of reasons. That X isn't an array, pointer or struct for
> example.

Yes, and you'll notice I did not point that out.  There are cases when
X.m is not a lvalue even when X is an expression of the right type to
have a member m.

> (BTW I've now counted the different categories of my own languages are
> there are about 15 in all that can be used as assignment targets. A lot are
> just terms that can appear as rvalues, that can also appear as lvalues.
>
> For example a 'switch' statement, which standard C doesn't even allow as an
> rvalue.
>
> Sorry, did your remark above suggest I don't know what an lvalue is?

That seemed like the obvious explanation for the incorrect information
you gave.  Did you post it /knowing/ what other kinds of things are
lvalues in C just to confuse people?

> Maybe
> it's a miracle all this stuff works then!)

-- 
Ben.