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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Register storage type |
| Date | 2011-05-14 16:46 -0700 |
| Organization | None to speak of |
| Message-ID | <lnfwoghml4.fsf@nuthaus.mib.org> (permalink) |
| References | (3 earlier) <lnaaerk3sg.fsf@nuthaus.mib.org> <_ZednX81cqTb9VDQnZ2dnUVZ_s-dnZ2d@bestweb.net> <iqk7t1$u3f$1@speranza.aioe.org> <ln1v02i5az.fsf@nuthaus.mib.org> <iqms36$vj1$1@speranza.aioe.org> |
Free Willy <nospam@nospam.com> writes:
> Keith Thompson writes:
[...]
>> Always remember that C and C++ are two different languages. The C++
>> semantics for "register" differ from the C semantics.
>>
>> <OT>
>> C++ 2003 7.1.1p3:
>> A register specifier has the same semantics as an auto specifier
>> together with a hint to the implementation that the object so
>> declared will be heavily used. [Note: the hint can be ignored and in
>> most implementations it will be ignored if the address of the object
>> is taken. —end note]
>> </OT>
>
> That's interesting, although I don't think it really explains it - I
> normally use g++ in C mode because it gives some extra type checking, eg
> prevents implicit typecasting of pointers.
I don't believe g++ has a C mode. g++ and gcc are part of the same
compiler collection; g++ is the C++ compiler, and gcc is the C compiler.
I suppose you mean that you use g++ to compile C code, but as you've
seen, this doesn't always work.
(OH, and you mean "implicit conversions". Casts are always explicit.)
> Personally I think the C++ way is better than the C way - it avoids
> problems if you try to assign more register variables than the machine
> has registers available, effectively in C++ it sounds like the compiler
> can "fall back" to discarding the register specification and treating it
> like a normal stack variable should there be no register available.
>
> I use the register keyword to tell the compiler that a variable is used a
> lot eg as a loop index. What I "really want" is for the compiler to
> optimize access to that variable - putting it in a register is only a
> means to an end!
"register" is a relic of earlier times with less intelligent optimizing
compilers. The compiler can figure out for itself that a variable is
used heavily, especially a local variable (which is all you can apply
"register" to anyway).
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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Register storage type Free Willy <nospam@nospam.com> - 2011-05-12 20:55 +0000
Re: Register storage type Kenneth Brody <kenbrody@spamcop.net> - 2011-05-12 17:02 -0400
Re: Register storage type Free Willy <nospam@nospam.com> - 2011-05-12 21:13 +0000
Re: Register storage type Angel <angel+news@spamcop.net> - 2011-05-12 21:20 +0000
Re: Register storage type Keith Thompson <kst-u@mib.org> - 2011-05-12 14:27 -0700
Re: Register storage type Kenneth Brody <kenbrody@spamcop.net> - 2011-05-13 13:20 -0400
Re: Register storage type Free Willy <nospam@nospam.com> - 2011-05-13 21:30 +0000
Re: Register storage type Keith Thompson <kst-u@mib.org> - 2011-05-13 15:50 -0700
Different languages (Was: Register storage type) gazelle@shell.xmission.com (Kenny McCormack) - 2011-05-14 08:58 +0000
Re: Different languages (Was: Register storage type) Dr Nick <3-nospam@temporary-address.org.uk> - 2011-05-14 10:09 +0100
Re: Register storage type Free Willy <nospam@nospam.com> - 2011-05-14 21:27 +0000
Re: Register storage type Ian Collins <ian-news@hotmail.com> - 2011-05-15 09:55 +1200
Re: Register storage type Keith Thompson <kst-u@mib.org> - 2011-05-14 16:46 -0700
Re: Register storage type Jens <jens.gustedt@gmail.com> - 2011-05-15 10:08 -0700
Re: Register storage type James Kuyper <jameskuyper@verizon.net> - 2011-05-15 14:09 -0400
Re: Register storage type David Thompson <dave.thompson2@verizon.net> - 2011-05-19 01:50 -0400
Re: Register storage type Stephen Sprunk <stephen@sprunk.org> - 2011-05-15 00:27 -0500
Re: Register storage type Angel <angel+news@spamcop.net> - 2011-05-15 12:56 +0000
Re: Register storage type Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-15 11:54 -0400
Re: Register storage type Seebs <usenet-nospam@seebs.net> - 2011-05-15 17:43 +0000
Re: Register storage type Tim Rentsch <txr@alumni.caltech.edu> - 2011-05-18 23:37 -0700
Re: Register storage type Seebs <usenet-nospam@seebs.net> - 2011-05-19 14:37 +0000
Drift: Linguistics (was Re: Register storage type) Kenneth Brody <kenbrody@spamcop.net> - 2011-05-19 13:17 -0400
Re: Register storage type Tim Rentsch <txr@alumni.caltech.edu> - 2011-05-19 11:05 -0700
Re: Register storage type Seebs <usenet-nospam@seebs.net> - 2011-05-19 19:08 +0000
Re: Register storage type Tim Rentsch <txr@alumni.caltech.edu> - 2011-05-24 00:39 -0700
Re: Register storage type Ian Collins <ian-news@hotmail.com> - 2011-05-20 07:46 +1200
Re: Register storage type Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-19 22:37 -0400
Re: Register storage type Michael Press <rubrum@pacbell.net> - 2011-05-25 12:57 -0700
Re: Register storage type pete <pfiland@mindspring.com> - 2011-05-15 09:09 -0400
Re: Register storage type Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-12 21:57 -0400
Re: Register storage type Angel <angel+news@spamcop.net> - 2011-05-12 21:14 +0000
Re: Register storage type gordonb.unc3q@burditt.org (Gordon Burditt) - 2011-05-13 07:49 -0500
Re: Register storage type Keith Thompson <kst-u@mib.org> - 2011-05-12 14:20 -0700
Re: Register storage type Seebs <usenet-nospam@seebs.net> - 2011-05-12 21:59 +0000
Re: Register storage type BGB <cr88192@hotmail.com> - 2011-05-12 15:50 -0700
Re: Register storage type Keith Thompson <kst-u@mib.org> - 2011-05-12 15:49 -0700
Re: Register storage type Seebs <usenet-nospam@seebs.net> - 2011-05-12 23:19 +0000
Re: Register storage type Keith Thompson <kst-u@mib.org> - 2011-05-12 16:29 -0700
Re: Register storage type Seebs <usenet-nospam@seebs.net> - 2011-05-13 00:15 +0000
Re: Register storage type Columbus sailed the ocean China Blue <chine.bleu@yahoo.com> - 2011-05-12 15:24 -0700
Re: Register storage type Peter Nilsson <airia@acay.com.au> - 2011-05-12 17:39 -0700
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