Path: csiph.com!eternal-september.org!feeder.eternal-september.org!nntp.eternal-september.org!.POSTED!not-for-mail From: Tim Rentsch Newsgroups: comp.lang.c Subject: Re: Are designated initializer supposed to zero padding? Date: Mon, 11 May 2026 18:15:50 -0700 Organization: A noiseless patient Spider Lines: 33 Message-ID: <86h5odpgvt.fsf@linuxsc.com> References: <10tqqso$kn23$1@dont-email.me> <86jytar6n2.fsf@linuxsc.com> <20260511232247.00006c5e@yahoo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Date: Tue, 12 May 2026 01:15:53 +0000 (UTC) Injection-Info: dont-email.me; logging-data="1654897"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+s542LiYDA+oaZtddCgsT/OLHnnVfo+po="; posting-host="714746643ff61f997ea29d517f63563d" User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.4 (gnu/linux) Cancel-Lock: sha1:bTSALpeDyFq70Gvw4cwR5HGGcMk= sha1:KhlntPuTAze8rTjH1RyNmwv0KWw= sha256:OQcHuE1jJw9qbff1+kUVWKxK/zx/GYh0NGtOGMD4+Wc= sha1:XNpGU7M6em5ZmNtd/OL27i/G6jM= Xref: csiph.com comp.lang.c:398789 Michael S writes: > On Sun, 10 May 2026 20:01:53 -0700 > Tim Rentsch wrote: > >> Point 1: initializers are not required to set padding (either >> padding bits or padding bytes). Don't expect padding to be >> zeroed. This statement applies to initializers in all forms - >> regular initializers, designated initializers, and compound >> literals. > > James Kuyper says that zeroing of padding is required by that standard. > I am not an expert in lawyer-style reading of the standard, but at my > level it looks that he is correct and the wording in unequivocal. > For example, n3220, 6.7.11: > > 11 > If an object that has automatic storage duration is not initialized > explicitly, its representation is indeterminate. If an object that has > static or thread storage duration is not initialized explicitly, or > any object is initialized with an empty initializer, then it is subject > to default initialization, which initializes an object as follows: > ? if it has pointer type, it is initialized to a null pointer; > ? if it has decimal floating type, it is initialized to positive zero, > and the quantum exponent is implementation-defined; > ? if it has arithmetic type, and it does not have decimal floating > type, it is initialized to (positive or unsigned) zero; > ? if it is an aggregate, every member is initialized (recursively) > according to these rules, and any padding is initialized to zero bits; Sorry, I had missed the crucial last part here, even after I had looked in multiple editions of the C standard. Mea culpa. Please see my response to Keith Thompson.