Theodoros Bebekis wrote:
> An recent coding error revealed that it is possible to pass a bounded array
> to a dynamic array. Here is how.
>
>
> type
> TIntArray = array of integer;
> PIntArray = ^TIntArray;
>
>
> (* helper, it displays the ref counter of a dynamic array *)
> procedure DisplayRefCount(A: TIntArray);
> var
> P : Pointer;
> begin
> P := A;
>
> P := Pointer(Integer(P) - 4);
> ShowMessage(IntToStr(PInteger(P)^));
That displays the array's length, not its reference count. Be careful
about passing empty arrays!
Also note that since you're passing the array non-const, the function
increments the reference count before proceeding with your code.
> (* I have the type address ($TYPEDADDRESS) compiler directive as {$T-}, the
> default
> setting, wich makes the @ operator to return an un-typed pointer.
> The fact that it is valid to pass an un-typed pointer to a typed pointer,
> is the source of the error
Yes, well, there's your problem. Always turn on the "typed @ operator"
compiler option. I've never understood why that's not the default. It
just makes so much more sense.
I think I asked about it once. Apparently, it's left turned off because
otherwise some perfectly valid code won't compile, requiring a
type-cast. Code that needs to equate, say, PInteger with PIntegerArray.
Also code that takes the address of a resourcestring to get a
PResStringRec. (The compiler thinks it has the type PString, which is
wrong.)
--
Rob
