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From: nobody@REPLAY.COM (Anonymous)
Subject: Re: System.Address_to_Access_Conversions
Date: 1998/07/14
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Date: 1998-07-14T00:00:00+00:00
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On Mon, 13 Jul 1998 16:42:29 GMT, jsanchor@my-dejanews.com wrote:

> Hello Everyone:  In my program I have some system address and I have to move
> data to it. I am using access types to do this. I don't want to use Unchecked
> conversion. So I started looking at a new feature Ada95 has
> System.Address_to_Access_Conversions. I have
> 
> type Dummy_Type is tagged private;
> type Ptr_to_Data_Type is access all Dummy_Type'class;
> 
> private
>   type Dummy_Type is tagged
>       record
>          checksum : Storage_Element;
>       end record;
> 
> Dummy       : Dummy_Type;
> Ptr_to_Data : Ptr_to_Data_Type;
> 
> 
> I want Ptr_to_Data to point to some system address, say, 16#00E00000#
> 
> ...
> 
> I tried using System.Address_to_Access_Conversions,
> 
> package Convert_to_Pointer is new
>          System.Address_to_Access_Conversions(system.address);

This should be instantiated for type Dummy_Type'Class.

> 
> Data_Ptr : Convert_to_Pointer.Object_Pointer;
> 
> Data_Ptr := Convert_to_Pointer(16#00E00000#); --This is my problem!!
> -- I need a type Ptr_to_Data_Type, NOT Convert_to_Pointer.Object_Pointer

Try using

subtype Ptr_To_Data_Type is Convert_to_Pointer.Object_Pointer;

If you instantiate Address_to_Access_Conversions for type
Dummy_Type'Class, then this gives you what you want (access all
Dummy_Type'Class).

> 
> I tried casting
> Ptr_to_Data := Ptr_to_Data_Type(Data_Ptr); --It compiled..but when I ran it
> SEGMENTATION FAULT ERROR showed up.
> Can anybody suggest how do I get the correct access type to point to memory.

At this point you have a pointer to System.Address that you've been able
(somehow) to convert to pointer to Dummy_Type'Class. That might have
something to do with the Segmentation Fault. However, manipulation of
arbitrary addresses is tricky; here your operating system is telling you
that you are accessing memory outside the area allocated to you.

> ...

Jeff Carter  PGP:1024/440FBE21
My real e-mail address: ( carter @ innocon . com )
"You brightly-colored, mealy-templed, cranberry-smelling, electric
donkey-bottom biters."
Monty Python & the Holy Grail

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