register variable

[macluvitch]

Hello folks

I often use register variables within functions (or as funcion parameters)
that reauired speed like searching for example . I know that it doesn't
mean that every register variable will be holded in register

so is there any rules to precize when using them
thanks

[Christopher Benson-Manica]

macluvitch <ma********@hot mail.com> spoke thus:

I often use register variables within functions (or as funcion parameters)
that reauired speed like searching for example . I know that it doesn't
mean that every register variable will be holded in register

Short answer: You're probably wasting your time, at best.

Long answer: Look a few threads down for the latest discussion of the
register keyword.

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[J. J. Farrell]

"macluvitch " <ma********@hot mail.com> wrote in message news:<8f******* *************** ********@localh ost.talkaboutpr ogramming.com>. ..

Hello folks

I often use register variables within functions (or as funcion parameters)
that reauired speed like searching for example . I know that it doesn't
mean that every register variable will be holded in register

so is there any rules to precize when using them

Yes - use them only when you want to prevent the code taking the address
of the variable.

[macluvitch]

ie: ?

[Arthur J. O'Dwyer]

On Sun, 2 May 2004, macluvitch wrote:

ie: ?

You've just posted three messages in a row like this: no context,
no content (at least, not in English). Consider forming a coherent
sentence or two. Make sure your readers know what you're talking
about. Quote context if it's necessary to your point. Google
"Usenet FAQ" if you don't know how to post to newsgroups; it's worth
your while.

FWIW, the '?' operator in C has nothing to do with the 'register'
keyword.

-Arthur

[Old Wolf]

jj*@bcs.org.uk (J. J. Farrell) wrote:

"macluvitch " <ma********@hot mail.com> wrote:

Hello folks

I often use register variables within functions (or as funcion parameters)
that reauired speed like searching for example . I know that it doesn't
mean that every register variable will be holded in register

so is there any rules to precize when using them

Yes - use them only when you want to prevent the code taking the address
of the variable.

The register keyword does not prevent code taking the address of the
variable. It is only an optimisation hint.

[Martin Ambuhl]

Old Wolf wrote:

The register keyword does not prevent code taking the address of the
variable. It is only an optimisation hint.

You are mistaken. Notice the word "Constraint s."

6.5.3.2 Address and indirection operators

Constraints

The operand of the unary & operator shall be either a
function designator, the result of a [] or unary * operator,
or an lvalue that designates an object that is not a bit-
field and is not declared with the register storage-class
specifier.

[Joona I Palaste]

Old Wolf <ol*****@inspir e.net.nz> scribbled the following:

jj*@bcs.org.uk (J. J. Farrell) wrote:

"macluvitch " <ma********@hot mail.com> wrote:

> Hello folks
>
> I often use register variables within functions (or as funcion parameters)
> that reauired speed like searching for example . I know that it doesn't
> mean that every register variable will be holded in register
>
> so is there any rules to precize when using them
Yes - use them only when you want to prevent the code taking the address
of the variable.

The register keyword does not prevent code taking the address of the
variable. It is only an optimisation hint.

If it didn't prevent code from taking the address of the variable, then
how would the compiler ever manage to optimise code that does take the
address of the variable?

--
/-- Joona Palaste (pa*****@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"Keep shooting, sooner or later you're bound to hit something."
- Misfire

[J. J. Farrell]

"Old Wolf" <ol*****@inspir e.net.nz> wrote in message
news:84******** *************** ***@posting.goo gle.com...

jj*@bcs.org.uk (J. J. Farrell) wrote:

"macluvitch " <ma********@hot mail.com> wrote:

Hello folks

I often use register variables within functions (or as funcion parameters) that reauired speed like searching for example . I know that it doesn't mean that every register variable will be holded in register

so is there any rules to precize when using them

Yes - use them only when you want to prevent the code taking the address
of the variable.

The register keyword does not prevent code taking the address of the
variable. It is only an optimisation hint.

Tell that to the Standard.

[Old Wolf]

Martin Ambuhl <ma*****@earthl ink.net> wrote:

Old Wolf wrote:

The register keyword does not prevent code taking the address of the
variable. It is only an optimisation hint.

You are mistaken.>
The operand of the unary & operator shall be either a
function designator, the result of a [] or unary * operator,
or an lvalue that designates an object that is not a bit-
field and is not declared with the register storage-class
specifier.

ACK. I should know by now not to go by what some compilers (even in
strict c99 mode) will accept.