Type t is MOD c???

Type t is MOD c???

[Magnus Hakansson]

This probably a very simple question when you know the answer, 
but it is causing me some troubble. In "system.ads" there is a
declaraton:

type Address is mod Memory_Size;

and I want to know how to assign a specific address to a pointer.
How do I do? What is the syntax for an "address"? Is there any 
hidden packages avilable for accessing certain bytes of the memory 
of my PC, or is there any other tricks I don't know? 

Can anyone help me on this subject?
                                                            ****
---                                                        ******
mvh mh                              __o           __        ***
                 _____/\          _`\<,_         /  \        I  __---___
__________-------       \________(o)/_(*)____---/    \---___-+-/        \

Re: Type t is MOD c???

[Vladimir Vukicevic]

In article <3h5bei$npp@nyheter.chalmers.se> Magnus Hakansson
<z94magh@mtek.chalmers.se> writes:
> This probably a very simple question when you know the answer, but
> it is causing me some troubble. In "system.ads" there is a
> declaraton:
>
> type Address is mod Memory_Size;
>
> and I want to know how to assign a specific address to a pointer.
> How do I do? What is the syntax for an "address"? Is there any
> hidden packages avilable for accessing certain bytes of the memory
> of my PC, or is there any other tricks I don't know?
>
> Can anyone help me on this subject?

You would do something like:

with System.Storage_Elements;
package Q is
	X : Integer;
	for X'Address use System.Storage_Elements.To_Address (16#ffff#);
end Q;

to access the Integer at address 16#ffff#.

The type Address is left as implementation-defined in the standard; in
GNAT, it's private. The 'Address attribute rep clause takes a
System.Address, so you have to use the functions in System.Storage_Elements
to convert an integer to an Address. (See RM9X5.0 13.3(10), 13.7, 13.7.1)

	- Vladimir

Re: Type t is MOD c???

[Robert Dewar]

Magnus Hakansson asks:

   This probably a very simple question when you know the answer,
   but it is causing me some troubble. In "system.ads" there is a
   declaraton:

   type Address is mod Memory_Size;

   and I want to know how to assign a specific address to a pointer.
   How do I do? What is the syntax for an "address"? Is there any
   hidden packages avilable for accessing certain bytes of the memory
   of my PC, or is there any other tricks I don't know?

   Can anyone help me on this subject?

Magnus, clearly you are using Ada 95 (probably GNAT, though you did not say).
Assigning an address to a pointer can be done, but is usually not the best way
of doing things instead use:

  for x'address use expr;

where x is a variable, and expr is an address. For how to construct an
address, see the type Integer_Address and associated routines in the
package System.Storage_Elements.

If you really need to convert an address to a pointer, see package
System.Address_To_Access_Conversions.