Re: auto const ints and pointer issue

[Karen Shaeffer <shaeffer at neuralscape dot com>]

Hi,
Hahaha! I know, I have been getting an education here. I
really appreciate everyone's patience on this issue. I
have assimilated all the excellent comments and understand
my own laziness has caused my confusion. Thank you all.
Karen

On Wed, Jun 18, 2008 at 11:20:00AM +0100, Andrew Haley wrote:
> Karen Shaeffer wrote:
> > On Tue, Jun 17, 2008 at 11:01:31AM -0700, Ian Lance Taylor wrote:
> >>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >>> ~~~~~~~~~~~~~~~~ output ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >>> $ const_ints 
> >>> const int ic = 0   *cip = 5   *ip = 5
> >>> &ic = 0xbfbd72a0    cip = 0xbfbd72a0    ip = 0xbfbd72a0
> >>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >>>
> >>> The global variable code would segfault, as I expected. But the
> >>> auto variable code gives this illogical result. I would appreciate
> >>> comments. I am not on this list, so please ensure I am cc'd with
> >>> any responses. I'll be happy to file a bug, if it is a bug.
> >> Modifying a variable which is declared const is undefined behaviour.
> >> You can not predict what happens.
> 
> > I can live with that. My problem was that the addresses cannot
> > be correct. In my opinion, the undefined behavior should be
> > limited to the value in the address or in some form of error.
> 
> Your opinion about undefined behaviour is not shared by the C
> Standard committee: undefined code may do anything.  As the
> saying goes, "Demons might fly our of your nose."
> 
> > But to let the buggy code execute with addresses that are not
> > accurate is a liberty I would hope could have been avoided. It
> > just looks bad. I do realize, no one should have a gripe, because
> > the code is buggy to begin with. But addresses should always be
> > reported accurately IMHO. Of course, I obviously know nothing
> > about compilers. (smiles ;)
> 
> For what it's worth, this is a common misunderstanding.  A proper
> understanding of the true meaning of "undefined behaviour" comes
> later.
> 
> Andrew.
---end quoted text---

-- 
 Karen Shaeffer
 Neuralscape, Palo Alto, Ca. 94306
 shaeffer@neuralscape.com  http://www.neuralscape.com