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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Regarding assignment to struct
Date: Sat, 03 May 2025 17:37:28 -0700
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Lawrence D'Oliveiro <ldo@nz.invalid> writes:
> On Sat, 3 May 2025 01:14:46 -0700, Andrey Tarasevich wrote:
>> Virtually every C project relies on assignment of structures.
>> Passing-returning structs by value might be more rare (although
>> perfectly valid and often appropriate too), but assignment...
>> assignment is used by everyone everywhere without even giving it a
>> second thought.
>
> There is a caveat, to do with alignment padding: will this always have a 
> defined value?

I don't believe so.  In a quick look, I don't see anything in
the standard that explicitly addresses this, but I believe that a
conforming implementation could implement structure assignment by
copying the individual members, leaving any padding in the target
undefined.

(A quibble about your wording: I don't believe padding has a "value"
as the term is used by the standard.)

The question is whether the "value" of a struct object consists
only of the values of its members.  I'd say it does, but unless
I'm missing something the standard doesn't say so explicitly.

Finally, why would you care?e

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */