🚀 go-pugleaf

David Vandevoorde (vandevod@cs.rpi.edu) wrote:
: >>>>> "TP" == Tom Payne <thp@cs.ucr.edu> writes:
: [...]
: TP> This is probably the hub of our difference: I have difficulty
: TP> imagining a reasonable architecture that does something other than
: TP> ignoring or trapping the reading of invalid pointers.  (Granted,
: TP> "reasonable" is in the eye of the beholder.)
: 
: On the contrary, I think it could be a quite common thing. Many
: architectures memory-map I/O and it's perfectly imaginible that:
: 
: 	int x = *p;
: 
: where p is an invalid pointer triggers some I/O operation because
: p happens to point into such an ``I/O area''. The standard cannot
: reasonably be expected to say what can or cannot happen in those
: cirucmstances.

Right!  Everyone agrees that dereferencing an invalid pointer should
yield undefined hehavior.  

By "reading of invalid pointers", I mean the reading of a pointer
object at a time when it happens to contain an invalid value, as in:
     delete p;
     cout << int(p);
which yields "undefined behavior" under the current standards.
As I understand memory-mapped I/O, it is the reading of those
I/O locations themselves that produces the side effects, not
simply reading the value of a pointer to one.

Tom Payne (thp@cs.ucr.edu)
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