🚀 go-pugleaf

pkt@lpi.liant.com (Scott Turner) writes:
|In article <1992Dec15.162202.11231@ucc.su.OZ.AU> John (Max) Skaller writes:
|It makes me uneasy, but I think Jim Adcock is correct: an implementation
|can define an extension, such as memory mapping, which overrides the usual
|execution time rules of C/C++, including the rule that pointers to the same
|object compare equal.  The rule that 1+1==2 would likewise be subject to
|"extension".

For C, this is my impression also.  Although I find the terminology
unfortunate; it's unsettling to think that a conforming implementation
could compile and run a conforming program - which could then compute
1+1 and get 3.

Has X3J16 adopted similar notions of conformity?


|Nevertheless, the C standard implies that the onus is on the invoker of memory 
|mapping to be aware of libraries and other code which may rely on the usual
|execution time rules of C/C++, such as the rule that pointers to the same
|object compare equal.  If we don't want libraries to make that assumption,
|then John (Max) Skaller is also correct to say
|
|> So the question is really whether the requirement that pointers to
|> the same object compare equal should be left implementation defined.

Here I would disagree.  I think the question is whether, if the C++
standard adopts the same notions of conformity as the C standard,
pointers to the same object should be required to compare equal
in a conforming program.

And the answer is _no_.  I hope this requirement would exist for
_strictly_ conforming programs.  And it might be _reasonable_ to
expect it to hold in conforming programs.  But in a conforming 
program which depends on behaviour undefined or unspecified by
the standard, none of the rules apply, so the standard doesn't
actually _require_ anything.  (It's not clear to me whether all
rules disappear if a program fails to be strictly programming
because it depends on implementation-defined behaviour, but it
doesn't depend on any undefined or unspecified behaviour.)

-- 
Patrick Smith
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