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Casting volatile and const variables

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  Casting volatile and const variables Ravi <nospam@null.invalid> - 2011-09-24 20:50 +0000
    Re: Casting volatile and const variables Richard Damon <news.x.richarddamon@xoxy.net> - 2011-09-24 17:19 -0400
      Re: Casting volatile and const variables Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-09-24 22:39 +0100
        Re: Casting volatile and const variables Uno <merrilljensen@q.com> - 2011-09-24 21:41 -0700

#10885 — Casting volatile and const variables

Hello friends~

I read on the internet,
that const and volatile
variable should not be
type casted. Can you
please tell me why
shouldn't we type cast
const and volatile
variables?

Regards

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#10886

On 9/24/11 4:50 PM, Ravi wrote:
> Hello friends~
>
> I read on the internet,
> that const and volatile
> variable should not be
> type casted. Can you
> please tell me why
> shouldn't we type cast
> const and volatile
> variables?
>
> Regards

The danger with casting const/volatile variables is that writing to a 
object that is const is undefined behavior, as is accessing a volatile 
object except as a volatile object.

If you have a variable of type "pointer to const x", it is ok to cast 
that to "pointer to x" and write through it, if the pointer actually 
points to a object that isn't const (you are allowed to safely place the 
address of a non const object into a pointer to const variable).

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#10888

Richard Damon <news.x.richarddamon@xoxy.net> writes:

> On 9/24/11 4:50 PM, Ravi wrote:
>> Hello friends~
>>
>> I read on the internet,
>> that const and volatile
>> variable should not be
>> type casted. Can you
>> please tell me why
>> shouldn't we type cast
>> const and volatile
>> variables?

An example might help.  Can you show some code that you think is covered
by this rule?  I ask, because as you have it worded, I don't see any
problem at all.

> The danger with casting const/volatile variables is that writing to a
> object that is const is undefined behavior, as is accessing a volatile
> object except as a volatile object.

Agreed if the first 8 words are deleted!  The trouble is that a cast on
a cont variable does no let you modify it, nor done one on a volatile
variable lets you access it as anything than the volatile type it is.  I
think you've corrected the OP's question to answer the they probably
should have asked.

> If you have a variable of type "pointer to const x", it is ok to cast
> that to "pointer to x" and write through it, if the pointer actually
> points to a object that isn't const (you are allowed to safely place
> the address of a non const object into a pointer to const variable).

Also agreed, but none of that has anything to do with the what OP asked!

As I said, it may be very close to what the OP wanted to ask.  Maybe they
read something about "casting away const" from the target type of a
pointer and turned that into "casting a const variable".  But it's also
possible that they read something quite wrong.  I'd like to see an
example first.

-- 
Ben.

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#10901

On 9/24/2011 2:39 PM, Ben Bacarisse wrote:
> Richard Damon<news.x.richarddamon@xoxy.net>  writes:
>
>> On 9/24/11 4:50 PM, Ravi wrote:
>>> Hello friends~
>>>
>>> I read on the internet,
>>> that const and volatile
>>> variable should not be
>>> type casted. Can you
>>> please tell me why
>>> shouldn't we type cast
>>> const and volatile
>>> variables?
>
> An example might help.  Can you show some code that you think is covered
> by this rule?  I ask, because as you have it worded, I don't see any
> problem at all.
>
>> The danger with casting const/volatile variables is that writing to a
>> object that is const is undefined behavior, as is accessing a volatile
>> object except as a volatile object.
>
> Agreed if the first 8 words are deleted!  The trouble is that a cast on
> a cont variable does no let you modify it, nor done one on a volatile
> variable lets you access it as anything than the volatile type it is.  I
> think you've corrected the OP's question to answer the they probably
> should have asked.
>
>> If you have a variable of type "pointer to const x", it is ok to cast
>> that to "pointer to x" and write through it, if the pointer actually
>> points to a object that isn't const (you are allowed to safely place
>> the address of a non const object into a pointer to const variable).
>
> Also agreed, but none of that has anything to do with the what OP asked!
>
> As I said, it may be very close to what the OP wanted to ask.  Maybe they
> read something about "casting away const" from the target type of a
> pointer and turned that into "casting a const variable".  But it's also
> possible that they read something quite wrong.  I'd like to see an
> example first.
>

example?
-- 
uno

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