Re: Generating Java Bytecode

Joe Hummel wrote:
:
: Bill Purvis <w.purvis@daresbury.ac.uk> wrote:
: >The Java VM does support the basic things you need for C's pointer
: >rules - it's the Java Compiler that excludes them.
:
: Actually, I think it's the JVM that excludes general pointers...
: But we have to be careful when we say "pointer". Ada has pointers,
: and working Ada-->bytecode compilers seem to exist. But I think the
: problem is in supporting general pointers, i.e. pointer arithmetic and
: pointers to any old location in RAM:
:
: void *p;
:
: p = (void *) 0x0080001F; /* some memory location */
: *((int *) p) = 10; /* let's store 10 there */
: p++;


Stop.
I'm no C legalist, but from what I understand about C "undefined
behavior", there is a perfect example of it (BTW, this concept
is very near to the concept of erroneous in Ada83).


And a given C compiler is able to do whatever it want with undefined
behavior, including rejecting the program at compile-time. Since you
will need to rewrite in part the compiler, it seems to me that this
would be a good idea in this case.


OTOH, if you really need such a program, then JavaVM and universality
and "protection" don't seem good features to me...


Cheers,


Antoine
[I believe that there are quite legal C programs that use pointer conversions
that are impossible in Java. Consider any call to malloc() which returns a
char * pointer that is invariably whomped into some other kind of pointer.
Yes, we could special-case malloc(), but you can equally well write your own
storage allocator which would have the same pointer behavior. -John]
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