Re: converting pointer to value

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2021-03-04 17:55, Shark8 wrote:

>> type SQLPOINTER is private;
> ....
>> private
>> type SQLPOINTER is new System.Storage_Elements.Integer_Address;
> 
> And here we have SQLPOINTER, which is private, but which is something of the same representation that Integer_Address has; let's assume that the ADDRESS type is implementation-defined, and a private type.

SQLPOINTER is System.Address.

> What does this mean?
> It means that we don't know what the size of ADDRESS (and thus SQLPOINTER) actually is, but assuming you're on a 32- or 64-bit machine it's likely 2 to 4 times as large as the 16-bit SQLSMALLINT-- which is a good indication that a simple UNCHECKED_CONVERSION is the wrong answer.

You need not to know that:

    declare
       P : SQLPOINTER := ...;
       A : System.Address;
       pragma Import (Ada, A);
       for A'Address use P'Address;
       T : My_Fancy_Object;
       pragma Import (Ada, My_Fancy_Object);
       for T'Address use A;
    begin
       ... -- Use T at P

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de