Pool Specific Access Types?

Pool Specific Access Types?

[Mr.Clueless]

Alright...I'm creating an access type like this...

type Number;

type Numb_pnt is access Number;

type Number is
       record
	  The_Numb: Integer;
	   Next: Numb_pt;
	end record;
	
	N: Numb_pnt;

Now I know I got that part right...but I'm running into a problem in
reading and assigning  numbers (or any other kind of data) from/to the
linked list.

For example, I'll assign a new value from a variable like this...

	N := new Number'(<variable>, N);

which seems to work alright.  But then when I try to read from it using a
procedure such as...

	function Sum(List: Cell_Ptr) return Integer is
	   Local: Cell_Ptr := List; S: Integer := 0;
	begin
		while Local /= null loop
		  S := S + Local.Value; Local := Local.Next;
		 end loop;
		return S;
	end Sum;

I get an error in s-valuns at line 85.  Note I'm using the above code
segment that I found in  the Barnes book. This is a Constraint Error that
pops up at runtime and terminates the program. I suspect I'm not passing
data to or reading data from the List correctly, but I'm following the
examples in the book by wrote.

Any advice would help. Note, I am using Ada.Text_IO so as to pull the
Integers in off a text  string entered by the user at runtime.

Thanks.

Clueless. 
chris@dont.spam.me

Re: Pool Specific Access Types?

[Ted Dennison]

In article <CvLl7.84584$K6.34880767@news2>, Mr.Clueless says...
>	function Sum(List: Cell_Ptr) return Integer is
>	   Local: Cell_Ptr := List; S: Integer := 0;
>	begin
>		while Local /= null loop
>		  S := S + Local.Value; Local := Local.Next;
>		 end loop;
>		return S;
>	end Sum;

It looks cool. Try stepping through this in the debugger, paying attention to S
and Local.Value. It could be that your ".Value" got huge numbers (garbage) in it
somehow. If you add two or more of those together, then I could see you getting
a Constraint_Error.

Another possibility is that you somehow ended up with a circular queue when you
built it, and it is just iterating around in a circle until you blow S past
Integer'Last.

---
T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html
          home email - mailto:dennison@telepath.com

Re: Pool Specific Access Types?

[James Rogers]

Could the problem be that your record is defined with two fields:
The_Numb and Next, while your loop is accessing two fields:
Value and Next? You also have your access type defined as Numb_pnt
while your Next field is defined as being type Numb_pt.

I suspect these are typos in your posting and not in your
code. It would be easier to diagnose the problem without such
errors.

Jim Rogers
Colorado Springs, Colorado USA

"Mr.Clueless" wrote:
> 
> Alright...I'm creating an access type like this...
> 
> type Number;
> 
> type Numb_pnt is access Number;
> 
> type Number is
>        record
>           The_Numb: Integer;
>            Next: Numb_pt;
>         end record;
> 
>         N: Numb_pnt;
> 
> Now I know I got that part right...but I'm running into a problem in
> reading and assigning  numbers (or any other kind of data) from/to the
> linked list.
> 
> For example, I'll assign a new value from a variable like this...
> 
>         N := new Number'(<variable>, N);
> 
> which seems to work alright.  But then when I try to read from it using a
> procedure such as...
> 
>         function Sum(List: Cell_Ptr) return Integer is
>            Local: Cell_Ptr := List; S: Integer := 0;
>         begin
>                 while Local /= null loop
>                   S := S + Local.Value; Local := Local.Next;
>                  end loop;
>                 return S;
>         end Sum;
> 
> I get an error in s-valuns at line 85.  Note I'm using the above code
> segment that I found in  the Barnes book. This is a Constraint Error that
> pops up at runtime and terminates the program. I suspect I'm not passing
> data to or reading data from the List correctly, but I'm following the
> examples in the book by wrote.
> 
> Any advice would help. Note, I am using Ada.Text_IO so as to pull the
> Integers in off a text  string entered by the user at runtime.
> 
> Thanks.
> 
> Clueless.
> chris@dont.spam.me

Re: Pool Specific Access Types?

[Mr.Clueless]

In article <WiMl7.6560$4z.25901@www.newsranger.com>, Ted
Dennison<dennison@telepath.com> wrote:

> In article <CvLl7.84584$K6.34880767@news2>, Mr.Clueless says...
>>	function Sum(List: Cell_Ptr) return Integer is
>>	   Local: Cell_Ptr := List; S: Integer := 0;
>>	begin
>>		while Local /= null loop
>>		  S := S + Local.Value; Local := Local.Next;
>>		 end loop;
>>		return S;
>>	end Sum;
> 
> It looks cool. Try stepping through this in the debugger, paying
> attention to S and Local.Value. It could be that your ".Value" got huge
> numbers (garbage) in it somehow. If you add two or more of those
> together, then I could see you getting a Constraint_Error.
> 
> Another possibility is that you somehow ended up with a circular queue
> when you built it, and it is just iterating around in a circle until you
> blow S past Integer'Last.

I tried loading it up using both GVD and GDB (They're both essentially the
same thing, I know.)

And I get the error right from the start "Cannot access memory at
<address>" 

I tried the same list with...

	while N /= null loop
		Put_Line( N.The_Numb'img); N := N.Next;
	end loop;

And got the exact same error message. Even when theres only one number in
the entire list. Even a 0 gives me this message.  At least in the book it
works. I even tried using...

	while N /= null loop
		numb_var := N.The_Numb; 
		Put_Line( numb_var'img ); 
		N := N.Next;
	end loop;

Thinking that maybe I needed to pull the number out of the list and assign
it to a static variable first. Same error.

Somethings fishy here.  I'm still working on it.

Thanks.

Clueless chris@dont.spam.me

Re: Pool Specific Access Types?

[Mr.Clueless]

In article <3B9797BF.B6FEA4A@worldnet.att.net>, James Rogers
<jimmaureenrogers@worldnet.att.net> wrote:

> Could the problem be that your record is defined with two fields:
> The_Numb and Next, while your loop is accessing two fields: Value and
> Next? You also have your access type defined as Numb_pnt while your Next
> field is defined as being type Numb_pt.
> 
> I suspect these are typos in your posting and not in your code. It would
> be easier to diagnose the problem without such errors.
> 
> Jim Rogers Colorado Springs, Colorado USA
> 
> "Mr.Clueless" wrote:
>> 
>> Alright...I'm creating an access type like this...
>> 
>> type Number;
>> 
>> type Numb_pnt is access Number;
>> 
>> type Number is
>>        record
>>           The_Numb: Integer;
>>            Next: Numb_pt;
>>         end record;
>> 
>>         N: Numb_pnt;
>> 
>> Now I know I got that part right...but I'm running into a problem in
>> reading and assigning  numbers (or any other kind of data) from/to the
>> linked list.
>> 
>> For example, I'll assign a new value from a variable like this...
>> 
>>         N := new Number'(<variable>, N);
>> 
>> which seems to work alright.  But then when I try to read from it using
>> a procedure such as...
>> 
>>         function Sum(List: Cell_Ptr) return Integer is
>>            Local: Cell_Ptr := List; S: Integer := 0;
>>         begin
>>                 while Local /= null loop
>>                   S := S + Local.Value; Local := Local.Next;
>>                  end loop;
>>                 return S;
>>         end Sum;


Your right, it is a typo.  Should read...

function Sum(List: Numb_ptr) return Integer is
	Local : Numb_ptr := List;  S : Inter := 0;
begin
	while Local /= null loop
		S := S + Local.The_Numb; Local := Local.Next;
	end loop; return S;
end Sum;

Also, I'm not sure how accessing two fields in a loop would cause an
error. I can possibly see issues with regards to scope, but it's a little
fuzzy. Perhaps a nested loop, one accessing the "The_Numb" value and the
other accessing the "Next" value would do it?

Clueless chris@dont.spam.me

Re: Pool Specific Access Types?

[Darren New]

"Mr.Clueless" wrote:
>         N: Numb_pnt;

Not that I have more than a textbook knowledge of Ada, 
but shouldn't this be 
   N : Numb_pnt := null;

Where do you initialize the tail of your linked list?
 
-- 
Darren New 
San Diego, CA, USA (PST). Cryptokeys on demand.

Re: Pool Specific Access Types?

[Ted Dennison]

In article <3B97AA97.1548F906@san.rr.com>, Darren New says...
>
>"Mr.Clueless" wrote:
>>         N: Numb_pnt;
>
>Not that I have more than a textbook knowledge of Ada, 
>but shouldn't this be 
>   N : Numb_pnt := null;
>
>Where do you initialize the tail of your linked list?

Sometimes its good to be explicit. However, all Ada pointers get automaticly
initialized to null, if you don't explicitly give an initialization.

---
T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html
          home email - mailto:dennison@telepath.com

Re: Pool Specific Access Types?

[James Rogers]

"Mr.Clueless" wrote:
> 
> Your right, it is a typo.  Should read...
> 
> function Sum(List: Numb_ptr) return Integer is
>         Local : Numb_ptr := List;  S : Inter := 0;
                                         ^^^^^
              Another transcription error
> begin
>         while Local /= null loop
>                 S := S + Local.The_Numb; Local := Local.Next;
>         end loop; return S;
> end Sum;
> 
> Also, I'm not sure how accessing two fields in a loop would cause an
> error. I can possibly see issues with regards to scope, but it's a little
> fuzzy. Perhaps a nested loop, one accessing the "The_Numb" value and the
> other accessing the "Next" value would do it?

There is nothing wrong with your logic. I must assume there is
something wrong with your syntax. 

Perhaps, if you posted some of the actual code, instead of your
manual transcriptions, we might be able to find your error.

Jim Rogers
Colorado Springs, Colorado USA

Re: Pool Specific Access Types?

[Stephen Leake]

"Mr.Clueless" <chris@dont.spam.me> writes:

> <snip> 
> Your right, it is a typo.  Should read...
> <snip>

If you post a _complete_, _compileable_ example, it would be _much_
easier to help.

-- 
-- Stephe

Re: Pool Specific Access Types?

[Warren W. Gay VE3WWG]

Ted Dennison wrote:
> In article <3B97AA97.1548F906@san.rr.com>, Darren New says...
> >
> >"Mr.Clueless" wrote:
> >>         N: Numb_pnt;
> >
> >Not that I have more than a textbook knowledge of Ada,
> >but shouldn't this be
> >   N : Numb_pnt := null;
> >
> >Where do you initialize the tail of your linked list?
> 
> Sometimes its good to be explicit. However, all Ada pointers get automaticly
> initialized to null, if you don't explicitly give an initialization.

Coming from a C/C++ background, this is one of the really _great_
features of Ada, that I continue to smile at!  :-)
-- 
Warren W. Gay VE3WWG
http://members.home.net/ve3wwg

Re: Pool Specific Access Types?

[Darren New]

> Sometimes its good to be explicit. However, all Ada pointers get automaticly
> initialized to null, if you don't explicitly give an initialization.

Cool beans. This I didn't know. 

-- 
Darren New 
San Diego, CA, USA (PST). Cryptokeys on demand.

Re: Pool Specific Access Types?

[Wannabe h4x0r]

In article <3B97ACBA.26FB053F@worldnet.att.net>, James Rogers
<jimmaureenrogers@worldnet.att.net> wrote:

> "Mr.Clueless" wrote:
>> 
>> Your right, it is a typo.  Should read...
>> 
>> function Sum(List: Numb_ptr) return Integer is
>>         Local : Numb_ptr := List;  S : Inter := 0;
>                                          ^^^^^
>               Another transcription error
>> begin
>>         while Local /= null loop
>>                 S := S + Local.The_Numb; Local := Local.Next;
>>         end loop; return S;
>> end Sum;
>> 
>> Also, I'm not sure how accessing two fields in a loop would cause an
>> error. I can possibly see issues with regards to scope, but it's a
>> little fuzzy. Perhaps a nested loop, one accessing the "The_Numb" value
>> and the other accessing the "Next" value would do it?
> 
> There is nothing wrong with your logic. I must assume there is something
> wrong with your syntax. 
> 
> Perhaps, if you posted some of the actual code, instead of your manual
> transcriptions, we might be able to find your error.
> 
> Jim Rogers Colorado Springs, Colorado USA

Your right. Sorry. I was afraid that readers of this group really didnt like the posting of 
whole programs, as they can get rather lengthy. But here it is anyways.

-- This is a file so I can learn how to do pointers in Ada95 --
-- Try not to laugh too much. I'm a former C junkie, and it shows. --

with Ada.Text_IO; use Ada.Text_IO;

procedure Point_pract is

	type Numb_holder;
	type Numb_ptr is access Numb_holder;

	type Numb_holder is
		record
		  Number: Integer;
		  Next:   Numb_Ptr;
		end record;

	N: Numb_ptr;

	s : string(1..15);
	len : natural;
	quit : constant String := "q";

	anthr_numb : integer := 0;

begin

	loop
		Put_Line("Enter a number here: ");
		Get_Line( s , len);
		if s /= quit then
			while N /= null loop
					
			   Put_Line( N.Number'img );
			   N := N.Next;	   
			  exit;						
			end loop;
		else										
	            anthr_numb := Integer'value(s(1..len));
                    N := new Numb_holder'(anthr_numb, N);

		New_Line;

		
	       end if;
	end loop;

end Point_pract;

Re: Pool Specific Access Types? Screw up in the previous post.

[Clueless]

I put an "exit;" statement inside the loop;  It shouldnt be there.

Ignore it. It does the same thing with or without the exit.

Blah. Too much caffiene.

Anyways...the program should loop indefinitely, until I hit "q"  and then
it should crap out...which is exactly what I wanted it to do.

Thanks.

Clueless chris@dont.spam.me

Re: Pool Specific Access Types?

[Ted Dennison]

In article <mqRl7.85388$K6.35118504@news2>, Wannabe h4x0r says...
>-- This is a file so I can learn how to do pointers in Ada95 --
>-- Try not to laugh too much. I'm a former C junkie, and it shows. --
>
>with Ada.Text_IO; use Ada.Text_IO;
>
>procedure Point_pract is
>
>	type Numb_holder;
>	type Numb_ptr is access Numb_holder;
>
>	type Numb_holder is
>		record
>		  Number: Integer;
>		  Next:   Numb_Ptr;
>		end record;
>
>	N: Numb_ptr;
>
>	s : string(1..15);
>	len : natural;
>	quit : constant String := "q";
>
>	anthr_numb : integer := 0;
>
>begin
>
>	loop
>		Put_Line("Enter a number here: ");
>		Get_Line( s , len);
>		if s /= quit then
s is a 15 character string, and quit is a 1 character string. They will *always*
be different, so you will never go to the else for this "if". You should instead
compare "s(s'first..len) /= quit"

>			while N /= null loop

N starts off null, and nothing reachable ever sets it, so the code inside this
loop won't run either.

Unreachable code:
>					
>			   Put_Line( N.Number'img );
>			   N := N.Next;	   
>			  exit;						
>			end loop;
>		else							

More unreachable code:		
>	            anthr_numb := Integer'value(s(1..len));
>                    N := new Numb_holder'(anthr_numb, N);
>
>		New_Line;
end Unreachable code.

>
>		
>	       end if;
>	end loop;
>
>end Point_pract;

Given this code, I'd expect to see a program that loops endlessly asking for a
number.

---
T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html
          home email - mailto:dennison@telepath.com

Re: Pool Specific Access Types? Thanks Ted...everyone.

[Clueless]

It finally works. Ted pointed out that I had my if/else backwards. 

Heres the code...does exactly what I'm expecting now. The Pool fills up
quite nicely...

-- This is a file so I can learn how to do pointers in Ada95 --
-- Try not to laugh too much. I'm a former C junkie, and it shows. --

with Ada.Text_IO; use Ada.Text_IO;

procedure Point_pract is

	type Numb_holder; type Numb_ptr is access Numb_holder;

	type Numb_holder is
		record
		  Number: Integer; Next:   Numb_Ptr;
		end record;

	N: Numb_ptr;

	s : string(1..15); len : natural; quit : constant String := "q";

	anthr_numb : integer := 0;

begin

	loop
		Put_Line("Enter a number here: "); Get_Line( s , len); if
		s(s'first..len) /= quit then
			anthr_numb := Integer'value(s(1..len)); N := new
			Numb_holder'(anthr_numb, N); New_Line;
		else
			N := N.Next;
			
			while N /= null loop
					
			   Put_Line( N.Number'img ); N := N.Next;	   
										
			end loop;										
		end if;
		
	end loop;

end Point_pract;

Now I can go over to a real program, and put this to use.

Thanks for your patience.

Clueless.

chris@dont.spam.me

Re: Pool Specific Access Types?

[Jeffrey Carter]

Wannabe h4x0r wrote:
> 
> with Ada.Text_IO; use Ada.Text_IO;
> 
> procedure Point_pract is
> 
>         type Numb_holder;
>         type Numb_ptr is access Numb_holder;
> 
>         type Numb_holder is
>                 record
>                   Number: Integer;
>                   Next:   Numb_Ptr;
>                 end record;
> 
>         N: Numb_ptr;
> 
>         s : string(1..15);
>         len : natural;
>         quit : constant String := "q";
> 
>         anthr_numb : integer := 0;
> 
> begin
> 
>         loop
>                 Put_Line("Enter a number here: ");
>                 Get_Line( s , len);
>                 if s /= quit then

S will never be equal to Quit. S'Length is 15, and Quit'Length is 1.

>                         while N /= null loop
> 
>                            Put_Line( N.Number'img );
>                            N := N.Next;
>                           exit;
>                         end loop;

This appears to be what you want to do when S = Quit. Is the test in
your "if" wrong?

>                 else
>                     anthr_numb := Integer'value(s(1..len));

This is what you do if S = Quit, which is never true. However, if it
were true, this call to Integer'Value would raise an exception, since S
(S'First .. Len) does not contain the textual representation of an
Integer.

>                     N := new Numb_holder'(anthr_numb, N);
> 
>                 New_Line;
> 
> 
>                end if;
>         end loop;
> 
> end Point_pract;


-- 
Jeffrey Carter