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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: lvalue types
Date: Mon, 02 Apr 2018 15:19:35 -0700
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Keith Thompson <kst-u@mib.org> writes:
[...]
> Given this program:
>
> #include <stdio.h>
> int main(void) {
>     struct s { int m; };
>     struct s obj = { 0 };
>     obj.m = 42;
>     printf("%d\n", obj.m);
> }
>
> Does the assignment `obj.m = 42;` modify the value of the object `obj.m`?
> Does the assignment `obj.m = 42;` modify the value of the object `obj`?
> (The phrase "modify the value of [the] object" is from the standard's
> definition of "access".)
[...]

I thought for a while that there might be something that would resolve
the oversight I saw in 6.5p7.

In the assignment expression

    obj.m = 42

there are two lvalues, `obj` and `obj.m`.  One could argue that obj is
accessed by the value `obj`, which is of type `struct s`.

But on further thought, that doesn't resolve it:

    struct s { int m; };
    struct s obj = { 0 };
    int *ptr = &obj.m;
    *ptr = 42;

In this assignment, there is no lvalue of type `struct s`, but the
object `obj` of type `struct s` is modified.

Oh well.

(I remain convinced that both obj.m and obj are accessed/modified
by the assignment.)

-- 
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"