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Groups > comp.lang.c > #105393
| From | BartC <bc@freeuk.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: C Names and Scopes |
| Date | 2017-03-04 22:37 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <o9ffep$ukg$1@dont-email.me> (permalink) |
| References | <o7duoo$vmp$1@dont-email.me> <o9d4q5$kjh$1@dont-email.me> <lnh938bz0w.fsf@kst-u.example.com> <o9f70r$1t5$1@dont-email.me> <6a58d8c5-3ba1-42c0-a089-95c6ce9c990f@googlegroups.com> |
On 04/03/2017 21:50, jameskuyper@verizon.net wrote:
> On Saturday, March 4, 2017 at 3:13:12 PM UTC-5, Bart wrote:
>> So what about struct member names? Here:
>>
>> struct {
>> struct {
>> int x,y,z;
>> } p;
>> struct {
>> int x,y,z;
>> } q;
>> };
>>
>> The two lots of x,y,z are isolated from here other. So they don't belong
>> to either the outer struct of the enclosing compound statement block or
>> to file-scope.
>
> You're confusing scopes with name spaces. Note that a "name space" is NOT the
> same thing as a C++ namespace. C++ also has the concept of a "name space", but
> it has fewer name spaces than C, using scopes instead. As a result, it says
> almost nothing about "name spaces".
>
> "... Different entities designated by the same identifier either have different
> scopes, or are in different name spaces. ..." (6.2.1p2)
> "... each structure or union has a separate name space for its members ... "
> (6.2.3p1)
>
> It's the fact that M is in the name space associated with struct FS that allows
> it to have the same name as a different member of a different struct type, even
> if that other member has a completely different type.
I don't think I'm confusing them, just maybe using them a little
differently. Here are the set of name-spaces I use in my implementation
(adapted from non-C code, they correspond to a set of enums):
ns_general, # vars, functions, typedefs, enum names
ns_tags, # struct, union, enum tags
ns_labels, # label names
ns_fields, # field names [ie. member names]
There are three main name-spaces ('general', 'tags' and 'labels'), which
allow the same identifiers to exist in the same lexical scope, provided
they have a different name-space attribute.
Field or member names are listed as having their own name-space, but
that is probably not necessary because in the lexical scopes in which
they exist, there will only be member names. Especially now that struct,
union and enum tags constructed on-the-fly have been banished elsewhere.
This would however have allowed member names to co-exist with such tags.
And it would have allowed this:
struct S {
struct S {
struct S {...
Name visibility is just as it would be for variables, types, and tags
defined in nested block scopes in a function.
> The obvious next question: why couldn't we do the same thing for struct tags?
> The key thing that allows struct members to have a different name space for
> each struct type, is that struct member names must ALWAYS be connected with a
> particular struct type
And any name in a block will always be connected with that block.
- normally, by a member selection operator whose first
> operand is (or points to) that specific struct type. That's the same reason why the offsetof() macro takes both a member name and struct type.
The language doesn't have a mechanism to make use of any other names
defined inside a struct (to make use of a handy struct definition for
example). Only by making them belong outside.
So struct (and enum) tags could have been treated just like member
names. The language decided not to do that, but it could just as easily
have chosen differently. There's nothing innate about struct tags that
they /have/ to be handled a certain way.
> In C++, where different struct types have different scopes, a similar construct
> is needed. It's the scope resolution operator "::", and would be used to
> distinguish between FS::MS (the first MS you defined) and ::MS (the second
> one). C's rules don't distinguish them, and therefore don't need the scope
> resolution operator to do so.
(In my languages, you can declare all sorts of things inside a struct.
The names of those things are local to that struct. They can be accessed
from outside with a qualified name (using "." rather than "::")
involving the struct type, or an instance of the struct. However this
was mainly because I neglected to prohibit such declarations. It seems
to work fine though...)
--
bartc
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C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 02:13 +0000
Re: C Names and Scopes David Brown <david.brown@hesbynett.no> - 2017-02-08 10:09 +0100
Re: C Names and Scopes mark.bluemel@gmail.com - 2017-02-08 02:37 -0800
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 11:07 +0000
Re: C Names and Scopes fir <profesor.fir@gmail.com> - 2017-02-08 09:03 -0800
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 17:19 +0000
Re: C Names and Scopes fir <profesor.fir@gmail.com> - 2017-02-08 09:42 -0800
Re: C Names and Scopes David Brown <david.brown@hesbynett.no> - 2017-02-08 12:08 +0100
Re: C Names and Scopes Moai <penultimategrill@gmail.com> - 2017-02-08 19:16 -0500
Re: C Names and Scopes David Brown <david.brown@hesbynett.no> - 2017-02-09 01:32 +0100
Re: C Names and Scopes Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-09 08:18 -0800
Re: C Names and Scopes Jerry Stuckle <jstucklex@attglobal.net> - 2017-02-09 12:06 -0500
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 10:51 +0000
Re: C Names and Scopes Thiago Adams <thiago.adams@gmail.com> - 2017-02-08 03:11 -0800
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 11:39 +0000
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 12:06 +0000
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 13:31 +0000
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 13:40 +0000
Re: C Names and Scopes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-08 16:39 +0000
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 17:51 +0000
Re: C Names and Scopes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-08 20:56 +0000
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 22:08 +0000
Re: C Names and Scopes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-08 23:27 +0000
Re: C Names and Scopes David Brown <david.brown@hesbynett.no> - 2017-02-08 13:41 +0100
Re: C Names and Scopes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-08 14:32 +0000
Re: C Names and Scopes supercat@casperkitty.com - 2017-02-08 07:28 -0800
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 20:12 +0000
Re: C Names and Scopes Keith Thompson <kst-u@mib.org> - 2017-02-08 12:38 -0800
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 21:54 +0000
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-08 22:40 +0000
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-09 18:48 +0000
Re: C Names and Scopes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-09 19:53 +0000
Re: C Names and Scopes Keith Thompson <kst-u@mib.org> - 2017-02-09 12:25 -0800
Re: C Names and Scopes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-09 21:27 +0000
Re: C Names and Scopes Keith Thompson <kst-u@mib.org> - 2017-02-09 13:57 -0800
Re: C Names and Scopes David Brown <david.brown@hesbynett.no> - 2017-02-13 10:54 +0100
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-10 00:26 +0000
Re: C Names and Scopes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-10 00:42 +0000
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-10 01:03 +0000
Re: C Names and Scopes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-10 01:49 +0000
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-10 12:31 +0000
Re: C Names and Scopes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-10 23:48 +0000
Re: C Names and Scopes supercat@casperkitty.com - 2017-02-10 16:06 -0800
Re: C Names and Scopes Keith Thompson <kst-u@mib.org> - 2017-02-10 16:22 -0800
Re: C Names and Scopes supercat@casperkitty.com - 2017-02-12 09:17 -0800
Re: C Names and Scopes Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-15 16:26 -0800
Re: C Names and Scopes Keith Thompson <kst-u@mib.org> - 2017-02-09 17:56 -0800
Re: C Names and Scopes supercat@casperkitty.com - 2017-02-10 07:42 -0800
Re: C Names and Scopes Keith Thompson <kst-u@mib.org> - 2017-02-10 08:44 -0800
Re: C Names and Scopes supercat@casperkitty.com - 2017-02-10 09:25 -0800
Re: C Names and Scopes Jerry Stuckle <jstucklex@attglobal.net> - 2017-02-10 16:43 -0500
Re: C Names and Scopes supercat@casperkitty.com - 2017-02-10 14:04 -0800
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-10 22:52 +0000
Re: C Names and Scopes Andrey Tarasevich <andreytarasevich@hotmail.com> - 2017-02-10 15:10 -0800
Re: C Names and Scopes Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-15 16:31 -0800
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-09 23:09 +0000
Re: C Names and Scopes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-09 23:36 +0000
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-02-10 00:19 +0000
Re: C Names and Scopes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-10 00:38 +0000
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-03-04 01:23 +0000
Re: C Names and Scopes jameskuyper@verizon.net - 2017-03-03 18:23 -0800
Re: C Names and Scopes GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-03-04 14:42 +0100
Re: C Names and Scopes "James R. Kuyper" <jameskuyper@verizon.net> - 2017-03-04 11:02 -0500
Re: C Names and Scopes GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-03-04 23:35 +0100
Re: C Names and Scopes Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-03-04 14:50 -0800
Re: C Names and Scopes Richard Heathfield <rjh@cpax.org.uk> - 2017-03-05 13:39 +0000
Re: C Names and Scopes GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-03-05 15:10 +0100
Re: C Names and Scopes Richard Heathfield <rjh@cpax.org.uk> - 2017-03-05 14:34 +0000
Re: C Names and Scopes Keith Thompson <kst-u@mib.org> - 2017-03-05 19:25 -0800
Re: C Names and Scopes raltbos@xs4all.nl (Richard Bos) - 2017-03-06 09:37 +0000
Re: C Names and Scopes Richard Heathfield <rjh@cpax.org.uk> - 2017-03-06 10:34 +0000
Re: C Names and Scopes James Kuyper <jameskuyper@verizon.net> - 2017-03-06 07:23 -0500
Re: C Names and Scopes GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-03-06 14:26 +0100
Re: C Names and Scopes Keith Thompson <kst-u@mib.org> - 2017-03-04 11:52 -0800
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-03-04 20:13 +0000
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-03-04 20:17 +0000
Re: C Names and Scopes Keith Thompson <kst-u@mib.org> - 2017-03-04 12:38 -0800
Re: C Names and Scopes jameskuyper@verizon.net - 2017-03-04 13:50 -0800
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-03-04 22:37 +0000
Re: C Names and Scopes jameskuyper@verizon.net - 2017-03-04 16:15 -0800
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-03-05 00:31 +0000
Re: C Names and Scopes jameskuyper@verizon.net - 2017-03-04 16:47 -0800
Re: C Names and Scopes BartC <bc@freeuk.com> - 2017-03-05 01:42 +0000
Re: C Names and Scopes jameskuyper@verizon.net - 2017-03-04 19:20 -0800
Re: C Names and Scopes Keith Thompson <kst-u@mib.org> - 2017-03-05 01:40 -0800
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