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| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Aliasing and subtyping structs |
| Date | 2016-11-01 15:27 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <87lgx3md9o.fsf@bsb.me.uk> (permalink) |
| References | <87oa1zgzw0.fsf@starless.ames.family> <87k2cngz0i.fsf@starless.ames.family> |
Andreas <nospam@invalid.invalid> writes:
> Following up to myself to add missing address operators to sample code:
>
> struct sub_type
> {
> uint8_t super_tag;
> ...
> };
>
> struct super_type
> {
> struct sub_type super;
> ...
> };
>
> struct hyper_type
> {
> struct super_type super;
> ...
> };
This looks odd to me. I'd expect more and more specific classes to be
progressively derived from a base class. Those derived classes would be
sub- (and sub-sub-classes). But this is a sketch so I might have the
wrong end of the stick.
> void foo (struct sub_type* base)
> {
> struct super_type* up = 0;
> struct hyper_type* upper = 0;
> if (base->super_tag == UP_ID)
> {
> up = (struct super_type*) base; // *NOT aliasing!?*
> ...
> }
> else if (base->super_tag == UP_ID)
> {
> upper = (struct hyper_type*) base; // *NOT aliasing!?*
> ...
> }
> ...
> }
>
> void bar (struct super_type* up, struct hyper_type* upper)
> {
> struct sub_type* base1 = (struct sub_type*) up; // *ALIASING?*
> struct sub_type* base2 = (struct sub_type*) upper; // *ALIASING?*
> struct sub_type* base3 = &up.super;
> struct sub_type* base4 = &upper.super.super;
(you need -> rather than the first .)
> ...
> }
You ask if your comments are correct. The trouble is that aliasing is a
very general word. In this context two pointers to the same object are
always aliases -- that's all it means -- so all of your pointer
assignments set up aliases.
I think what you are asking is whether the aliases conflict with places
where the compiler may assume that no aliasing is taking place. That
will crop up in places where you don't have any comments. For example
since 'up' and 'upper' are pointers to distinct types, the compiler may
assume that they do not alias.
Unfortunately I can't follow what you are doing in enough detail to
comment on whether it's OK or not.
--
Ben.
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Aliasing and subtyping structs Andreas <nospam@invalid.invalid> - 2016-11-01 13:15 +0100
Re: Aliasing and subtyping structs Andreas <nospam@invalid.invalid> - 2016-11-01 13:34 +0100
Re: Aliasing and subtyping structs Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-01 15:27 +0000
Re: Aliasing and subtyping structs Andreas <nospam@invalid.invalid> - 2016-11-02 09:47 +0100
Re: Aliasing and subtyping structs Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-02 15:47 +0000
Re: Aliasing and subtyping structs Andreas <nospam@invalid.invalid> - 2016-11-08 00:24 +0100
Re: Aliasing and subtyping structs supercat@casperkitty.com - 2016-11-07 21:42 -0800
Re: Aliasing and subtyping structs <william@wilbur.25thandClement.com> - 2016-11-03 18:53 -0700
Re: Aliasing and subtyping structs supercat@casperkitty.com - 2016-11-04 09:56 -0700
Re: Aliasing and subtyping structs Andreas <nospam@invalid.invalid> - 2016-11-08 21:53 +0100
Re: Aliasing and subtyping structs James Kuyper <jameskuyper@verizon.net> - 2016-11-01 11:41 -0400
Re: Aliasing and subtyping structs Andreas <nospam@invalid.invalid> - 2016-11-02 09:55 +0100
"Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Anton Shepelev <anton.txt@g{oogle}mail.com> - 2016-11-21 16:59 +0300
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] supercat@casperkitty.com - 2016-11-21 07:32 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] "James R. Kuyper" <jameskuyper@verizon.net> - 2016-11-21 11:15 -0500
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] supercat@casperkitty.com - 2016-11-21 08:35 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Anton Shepelev <anton.txt@g{oogle}mail.com> - 2016-11-22 11:42 +0300
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] supercat@casperkitty.com - 2016-11-22 06:50 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-22 16:07 +0000
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] supercat@casperkitty.com - 2016-11-22 12:02 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-11-22 23:36 +0000
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] supercat@casperkitty.com - 2016-11-22 16:24 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Richard Damon <Richard@Damon-Family.org> - 2016-11-22 22:21 -0500
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] supercat@casperkitty.com - 2016-11-23 08:31 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] me <crisdunbar@gmail.com> - 2016-11-23 09:01 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] supercat@casperkitty.com - 2016-11-23 12:05 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Anton Shepelev <anton.txt@gmail.com> - 2016-11-22 23:23 +0300
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] "James R. Kuyper" <jameskuyper@verizon.net> - 2016-11-22 16:02 -0500
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] supercat@casperkitty.com - 2016-11-22 14:13 -0800
Re: container_of() macro Noob <root@127.0.0.1> - 2016-11-23 01:10 +0100
Re: container_of() macro <william@wilbur.25thandClement.com> - 2016-11-22 20:10 -0800
Re: container_of() macro "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-11-23 15:10 -0800
Re: container_of() macro David Brown <david.brown@hesbynett.no> - 2016-11-23 11:31 +0100
Re: container_of() macro Anton Shepelev <anton.txt@g{oogle}mail.com> - 2016-11-23 14:07 +0300
Re: container_of() macro supercat@casperkitty.com - 2016-11-23 08:41 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Anton Shepelev <anton.txt@gmail.com> - 2016-11-30 00:14 +0300
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] "James R. Kuyper" <jameskuyper@verizon.net> - 2016-11-29 17:23 -0500
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Anton Shepelev <anton.txt@gmail.com> - 2016-12-04 18:48 +0300
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] "James R. Kuyper" <jameskuyper@verizon.net> - 2016-12-04 12:17 -0500
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Anton Shepelev <anton.txt@gmail.com> - 2016-12-04 22:15 +0300
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] "James R. Kuyper" <jameskuyper@verizon.net> - 2016-12-04 15:06 -0500
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Anton Shepelev <anton.txt@gmail.com> - 2016-12-12 22:31 +0300
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-11-23 13:39 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] luser droog <luser.droog@gmail.com> - 2016-11-23 15:10 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-11-23 15:13 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] luser droog <luser.droog@gmail.com> - 2016-11-23 18:29 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Anton Shepelev <anton.txt@g{oogle}mail.com> - 2016-11-24 11:41 +0300
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Thiago Adams <thiago.adams@gmail.com> - 2016-11-24 03:29 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-11-24 17:37 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] supercat@casperkitty.com - 2016-11-25 09:55 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Thiago Adams <thiago.adams@gmail.com> - 2016-11-25 15:22 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-11-28 18:18 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Thiago Adams <thiago.adams@gmail.com> - 2016-11-29 04:48 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] supercat@casperkitty.com - 2016-11-29 07:28 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Thiago Adams <thiago.adams@gmail.com> - 2016-11-30 08:26 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] supercat@casperkitty.com - 2016-11-30 09:13 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-12-12 16:44 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Melzzzzz <mel@zzzzz.com> - 2016-12-13 02:18 +0100
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Thiago Adams <thiago.adams@gmail.com> - 2016-12-14 09:47 -0800
Re: "Object-oriented programming in C" [was: Re: Aliasing and subtyping structs] Thiago Adams <thiago.adams@gmail.com> - 2016-12-14 10:14 -0800
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