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...r [basic.stc.static]. Anyway, I'm 99% sure that's supposed to be referring to user-allocated memory; the lifetime of an non-user-allocated object is permanently attached to its scope, so it's already gone before anything could be allocated on top of it. > The current consensus among CoreWG experts is that the words in the current standard (and those in the current WP) do not require distinct variables and temporaries to have distinct addresses per se. Then what's the alternative model? -Eli

On Oct 16, 2008, at 12:22 AM, Eli Friedman wrote: [...] >> The current consensus among CoreWG experts is that the words in the > current standard (and those in the current WP) do not require distinct > variables and temporaries to have distinct addresses per se. > > Then what's the alternative model? That if two complete objects can never be distinguished by observing th...

On Thu, Oct 16, 2008 at 7:04 AM, David Vandevoorde <daveed at vandevoorde.com> wrote: > > On Oct 16, 2008, at 12:22 AM, Eli Friedman wrote: > [...] >>> The current consensus among CoreWG experts is that the words in the >> current standard (and those in the current WP) do not require distinct >> variables and temporaries to have distinct addresses per se. >> >> Then what's the alternative model? > > > That if two complete objects can never be di...

...ed with a const type can be merged, meaning > that objects with the same value may (implementation defined or > unspecified) refer to the address of one of them. A rule like this > could be added to C or C++, but has not been to the best of my > knowledge. The current consensus among CoreWG experts is that the words in the current standard (and those in the current WP) do not require distinct variables and temporaries to have distinct addresses per se. (In most cases, distinct addresses are the only possible implementation, but even without const qualification there are cases...

On Oct 15, 2008, at 1:09 PM, David Vandevoorde wrote: > On Oct 15, 2008, at 3:53 PM, Mike Stump wrote: > [...] >> Objects are defined like so: >> >> Two pointers of >> the same type compare equal if and only if they are both null, >> both >> point to the same object or function, or both point one past the >> end >> of the same array.

On Oct 15, 2008, at 9:43 AM, Duncan Sands wrote: >> True, but note that it is the address of a variable that is used, not >> the value. > > Yes, but why do you think they should get a different address? I can > understand that it is surprising that they do, but determining whether > this is legal or not requires reading the language standard. > Hopefully > a

...he foremost experts on this topic), and so far we don't have > a definite answer (we're looking at C99 and C++). We do think that a > strict reading of the standard allows the optimization, but there is > also some suspicion that that is unintended (at least in C++). FWIW, a C++ CoreWG issue has been opened to clarify this. (My own position is that different objects should have guaranteed different addresses. To alias them, a code generator must prove that it wouldn't change observable behavior.) Daveed