🚀 go-pugleaf

joe (j.) halpin (jhalpin@bnr.ca) wrote:
: To Moderator: This may be a duplicate, my newsreader software was having
: trouble sending this, so I'm mailing it as well.
: 
: In 3.7.3.2.4 the January working paper says:
: 
: 4 A deallocation function can free the storage referenced by the pointer
:   given  as  its  argument and renders the pointer invalid.  The storage
:   can be made available for further allocation.  An invalid pointer con-
:   tains an unusable value:  it cannot even be used in an expression.
[...]
: Am I misunderstanding something, or is it illegal to zero out pointers
: after they've been deallocated? I'm assuming that the intent was to
: disallow dereferencing of pointers that have been handed to
: delete. The wording seems to disallow the above as well.
:
: In fact, it sounds like it also rules out things like 'if(pc == 0)
: ...' after the above fragment.

Apparently there are architectures (80386?) that perform such validity
checks on read access to pointer registers and trap on certain bogus
values.  So, the standard deems that after deallocation a pointer
object might contain a value that is so bogus that even reading it
will provoke "undefined behavior" and assigning the pointer a valid
value is the only valid operation.  It seems that to accomodate
certain hardware-based validity checkers for pointers, the standard
has precluded the possibility of portable software-based validity
checking.  IMHO an unfortunate decision.

Tom Payne (thp@cs.ucr.edu)
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