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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: C scope and struct definitions |
| Date | 2012-06-23 16:18 -0700 |
| Organization | None to speak of |
| Message-ID | <ln395l8vny.fsf@nuthaus.mib.org> (permalink) |
| References | <mYGdnXsGt41dNnnSnZ2dnUVZ_u-dnZ2d@bestweb.net> <js2buv$evv$1@dont-email.me> <js2s92$35s$1@speranza.aioe.org> <js32rk$siv$1@dont-email.me> <js5ekh$lug$1@speranza.aioe.org> |
pacman@kosh.dhis.org (Alan Curry) writes:
> In article <js32rk$siv$1@dont-email.me>,
> Eric Sosman <esosman@ieee-dot-org.invalid> wrote:
>>On 6/22/2012 6:40 PM, Alan Curry wrote:
>>>
>>> But is the compiler right for a real reason, or is it just a
>>> continuation of a historical accident? Why would you ever want this
>>> behavior?
>>
>> The Rationale sheds no light my tired old eyes can see. You
>>are welcome to read it for yourself. (Also, if you think the
>>normative text of the formal definition of the C language does not
>>qualify as "a real reason," well ...)
>
> The standard was supposed to codify existing practice. A real reason
> would have to come from before standardization. Was there a real
> reason for the existence of such a small, useless scope?
Yes: it's not useless.
>>
>>> I don't even see why you'd ever want any scope for a struct type other than
>>> "from here to the end of the file". Types are global things.
>>
>> Say, what?
>>
>> void f(void) {
>> static const struct foo {
>> const char *roman;
>> int decimal;
>> } table[] = { { "I", 1 }, { "II", 2 }, ... };
>> ...
>> }
>>
>> void g(void) {
>> struct foo {
>> double payload;
>> struct foo *next;
>> } *head, *p, *q;
>> ...
>> }
>>
>>Do you seriously maintain that these two `struct foo' types
>>should conflict with each other? If so, why? Explain why you
>>feel it is Wrong for a function to declare and use its own
>>private type for its own purposes, and why f() should have to
>>worry about what g() does in the privacy of its own block.
>
> I don't think we'd be losing anything if those declarations were simply
> illegal. Declare your structs before your functions. They aren't variables.
We'd lose backward compatibility; it would break existing code. I've
seen plenty of small programs that define types inside main (or
would you make main a special case?).
Nothing stops you from declaring your structs at file scope if you
want to, and I agree that it's *usually* the best thing to do.
But if a given type happens to be used only inside one function,
or even inside one block, the language allows you to declare it
there without polluting the rest of the program's namespace.
> A struct describes the procedure for interpreting bits in memory. As a
> procedure description, it's more like a function than a variable. It doesn't
> occupy memory itself, so it doesn't have a lifetime that can end when the
> function call ends. Putting it inside the function gives you nothing.
We're talking about scope, not lifetime. Types don't have lifetime,
but like any other declared entity, they do have scope (the region
of source code over in they're visible).
The scope rules for types are consistent with the scope rules for
objects. This consistency makes the language simpler, and has no
real cost that I can see. Again, if you don't want to declare types
at block scope, then by all means don't.
[...]
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Will write code for food.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-22 13:30 -0400
Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-22 14:02 -0400
Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-22 22:40 +0000
Re: C scope and struct definitions Ben Pfaff <blp@cs.stanford.edu> - 2012-06-22 15:47 -0700
Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-22 20:32 -0400
Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-23 22:06 +0000
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-23 16:18 -0700
Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-25 10:19 -0400
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-25 11:51 -0700
Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-23 19:54 -0400
Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-24 00:56 +0000
Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-23 21:48 -0400
Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-24 06:03 +0000
Re: C scope and struct definitions nick_keighley_nospam@hotmail.com - 2012-06-25 00:05 -0700
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-23 19:25 -0700
Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-24 05:40 +0000
Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-24 10:47 +0200
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-24 11:00 -0700
Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-25 03:53 +0000
Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-25 01:14 -0400
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-24 22:38 -0700
Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-25 11:03 -0400
Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-26 20:08 +0000
Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-26 23:21 +0200
Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-26 21:47 +0000
Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-26 18:05 -0400
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-26 16:45 -0700
Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-27 08:26 +0200
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 00:01 -0700
Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-27 06:57 -0400
Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-27 15:00 -0400
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 14:48 -0700
Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-27 16:14 -0700
Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-29 09:36 -0700
Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-27 16:27 -0700
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 12:03 -0700
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 12:11 -0700
Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-27 15:53 -0700
Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-26 17:59 -0400
Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-26 22:18 +0000
Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-26 18:33 -0400
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-26 17:22 -0700
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 00:03 -0700
Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-27 14:13 -0400
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 12:15 -0700
Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-29 09:43 -0700
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-29 11:59 -0700
Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-01 18:32 -0700
Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-27 20:59 +0000
Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-28 16:42 -0400
Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-23 20:57 -0400
Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-23 22:11 -0400
Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-23 22:51 -0400
Re: C scope and struct definitions Nick Bowler <nbowler@draconx.ca> - 2012-06-25 17:31 +0000
Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-25 14:46 -0400
Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-25 14:43 -0700
Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-26 13:44 +0200
Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-23 20:07 -0700
Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-24 10:56 +0200
Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-24 08:29 -0400
Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-24 10:26 -0700
Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-25 10:50 -0400
Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-24 09:23 -0700
Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-25 11:17 -0400
Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-25 14:22 -0700
Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-25 11:11 -0400
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