On 9 Sep, 09:47, Alan Fitch <alan.fi...@spamtrap.com> wrote:
> Tricky wrote:
> > the following code works, and Im just making sure that it is garanteed
> > to work and Im not just hitting some luck that the pointer address has
> > remained constant this time only. Look at the following code:
>
> > * process
> > * * *type a_p_t is access integer;
>
> > * * *variable ap1 : a_p_t;
> > * * *variable ap2 : a_p_t;
> > * begin
> > * * ap1 := new integer;
> > * * ap1.all := 1;
>
> > * * ap2 := ap1;
>
> > * * DEALLOCATE(ap1);
>
> > * * ap1 := new integer;
> > * * ap1.all := 5;
>
> > * * echo(integer'image(ap2.all) & LF);
> > * * wait;
> > * end process;
> > ......
>
> > I thought that ap2 would hold be a copy of the origional ap1,
> > therefore when new memory was alocated you couldnt garantee that ap2
> > would now point to the correct place, and in this case when I run it
> > Im just lucky ap1 doesnt change when a new integer is created?. or Is
> > it actually the case that the address will hold valid for ever, and
> > ap2 will now always point to the value inside ap1.
>
> Hi Tricky,
> * *from the VHDL 2002 LRM p47
>
> "NOTE—If an access value is copied to a second variable and is then
> deallocated, the second variable is not set to null
> and thus references invalid storage."
>
> So there is no guarantee that ap2.all will work, as far as I can see.
> I expect you have just been lucky.
>
> > am I correct in thinking, that if I assign ap1 to something else, ap2
> > then wont work?
>
> No I don't think so. I would guess that in your case with your
> particular simulator it may well carry on working - but that is just
> luck. You could try it and see!
>
> regards
> Alan
>
> --
> Alan Fitch
> Senior Consultant
>
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Thanks Alan.
On further messing around, I have seen it break. I have also seen it
run fine once, and after a restart and run again, the simulator hangs
(I think because its trying to allocated already leaked memory, and it
doesnt like it).
This was all in modelsim. Looks like Im going to have to move into
pointers to pointers for what I need to do.
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