Re: put of access type

[Rob Solomon <usenet@drrob1-noreply.com>]

On Wed, 19 Aug 2009 21:54:05 -0400, Rob Solomon
<usenet@drrob1-noreply.com> wrote:

>>> >You probably meant the address of the pointed object. Here you go. Let Ptr
>>> >be a pointer to some object
>>>
>>> >(with System.Storage_Elements; �use System.Storage_Elements;)
>>>
>>> > � Integer_Address'Image (To_Integer (Ptr.all'Address)));
>>>
>>> >Ptr.all'Address is the address of the object. To_Integer converts the
>>> >address to a plain integer type (Integer_Address defined in
>>> >System.Storage_Elements). This type can be output as any other.
>>>
>>> I am trying to understand this. �
>>>
>>> Back when I learned Modula-2, I learned that pointer types are
>>> assignment compatible with System.Address and I understand them as
>>> being the same thing. �They �differ in context, not value.
>>>
>>> I see that access types are being used the same as pointer types, but
>>> if I understand correctly, are actually quite different. �But I don't
>>> understand how. �ie, how are access types and pointers different?
>>
>>For simple types (integer; simple records) there's probably no
>>difference. For types with constraints/discriminants, bets are off:
>>consider
>>
>>  S : access String := "foo";
>>
>>S will most likely (this is compiler-dependent) *not* point to the 'f'
>>in "foo"; it might point to a structure containing
>>
>>   4-byte integer, lower bound of string (= 1)
>>   4-byte integer, upper bound of string (= 3)
>>   1-byte character = f
>>   1-byte character = o
>>   1-byte character = o
>>
>>> What is the difference between integer_address and address?
>>
>>integer_address is some sort of integer, with 'image, "=", "-" etc;
>>address is private, with no such operations (it does have comparators;
>>see package System).
>>
>>integer_address'image is going to be up to about 10 (32-bit addresses)
>>or 20 (64-bit addresses) characters long, and you are assigning it to
>>a string of length 255; that won't work.
>
>This is what I came up with, that works.  But I have another question,
>to follow the code:
>
>procedure adr is
>
>   type card32 is mod 4_294_967_296;
>   package card32_IO is new Ada.Text_IO.Modular_IO(card32);
>
>
>   X : aliased Integer := 1;
>   c,k : card32 := 0;
>
>   P1,P2,P3 : Access Integer;
>   Str,S : String(1..255);
>   begin
>   P1 := X'Access;
>   P2 := P1;
>   P3 := new integer;
>
>Ada.Strings.Fixed.Move(Integer_Address'Image(To_Integer(P1.all'Address)),Str);
>   Move(System.Address_Image(P1.all'address),s);
>   C   :=
>card32'value(Integer_Address'Image(To_Integer(P2.all'Address)));
>   K   :=
>card32'value(Integer_Address'Image(To_Integer(P3.all'Address)));
>   put("Str = ");
>   put(Str);
>   new_line;
>   put("s = ");
>   put(s);
>   put("C = ");
>   Card32_io.put(c);
>   new_line;
>   put("K = ");
>   Card32_io.put(k);
>   new_line;
>   end adr;
>
>My question is that the value of Str and S should be equal, after
>converting  hex <-> decimal.  They are not.  I am getting this as the
>relevent output
>Str = 3215841220
>S = BFADD7C4
>
>These numbers are not equal, according to my conversion.
>
>What am I missing?

NEVERMIND

I figured it out.  The output is not putting all digits on the same
line.  When I corrected for this, the actual output does match when
converting from hex <-> dec