help: String Sets in ADA???

help: String Sets in ADA???

[Arash Vahidi]

Hi' everyone

I'm an Ada-newbie and have a newbie question for you older guys :
How do you write a String-Set in adda without knowing the range of used
strings??
Here is my code, but lloks like I get Cosntraint_Error as soon as I make
an assigment (see the code).
Can I use some kind of pointers here ?? If yes, how?? (I tried every
forms of "access" and "'address" combinations I could think of)

If you come up with somthing, please let me know (vahidi@cd.chalmers.se)

Thanks for any help
  /Arash



----------------------------------   
with Ada.Text_Io; use Ada.Text_Io;


package body String_Set is

   type Node;
   type Node_Pointer is access Node;
   
   -- subtype String_Pointer is String(1..1024);  
   -- type String_Pointer is new String(1..1024);
   
   type Node is record
      Object : String( 1..1024 );
      -- Object : String_Pointer;
      Next   : Node_Pointer;
   end record;              
         
   First : Node_Pointer;
   
   procedure Init is
   begin
      First := null;
   end;

      
   procedure Insert( Object : in String) is
      Tmp : Node_Pointer;
   begin
      if in_Set( Object) = true then
         return;
      end if;
      
      if First = null then
         First := new Node;
         -- First.Object := String_Pointer(Object);
         First.Object := object;
         First.Next := null;
      else
         Tmp := First;
         loop exit when Tmp.Next = null;
            Tmp := Tmp.Next;
         end loop;         
         Tmp.Next := new Node;
         Tmp := Tmp.Next;
         Tmp.Object := Object;
         Tmp.Next := null;         
      end if;               
   end;      
                  
         
   function Is_Empty return Boolean is
   begin
      return First = null;
   end;
      
   function In_Set(Object : in String) return Boolean is
      Tmp : Node_Pointer;
   begin   
      Tmp := First;
      loop exit when Tmp = null;         
         if Tmp.Object = Object then
            return True;
         end if;            
         Tmp := Tmp.Next;         
      end loop;                           
      return False;
   end;
   
end String_Set;       

----------------------------------

Re: help: String Sets in ADA???

[Bob Fletcher]

It might be worth having a look at the standard library package
Ada.Strings_Unbounded. This has an implementation of a string class that
can be of any length, and can dynamically change over its lifetime. I don't
know if there are any issues regarding run-time overheads when using it,
but I don't imagine there would be.
-- 
Bob Fletcher
Consultant, Logica UK

// All opinions are my own, not my employers'

Arash Vahidi <vahidi@ios.chalmers.se> wrote in article
<360B9AFA.1F99D1CD@ios.chalmers.se>...
> Hi' everyone
> 
> I'm an Ada-newbie and have a newbie question for you older guys :
> How do you write a String-Set in adda without knowing the range of used
> strings??

Re: help: String Sets in ADA???

[dennison]

In article <360B9AFA.1F99D1CD@ios.chalmers.se>,
  Arash Vahidi <vahidi@ios.chalmers.se> wrote:

Having troube with our homework, are we? :-)

> Here is my code, but lloks like I get Cosntraint_Error as soon as I make
> an assigment (see the code).
...
>    type Node is record
>       Object : String( 1..1024 );
>       -- Object : String_Pointer;
>       Next   : Node_Pointer;
>    end record;
...
>    procedure Insert( Object : in String) is
>       Tmp : Node_Pointer;
>    begin
...
>          First.Object := object;
This line  ^^^^^^^^^^^^^^^^^^^^^^^ will raise a constraint error if the string
passed in to Insert isn't *exactly* 1024 characters long. You could change it
to:
   First.Object(1..Object'length) := Object;

If you want the rest of the string blanked out, you could add another line:
   First.Object (Object'length + 1..First.Object'last) := (others => ' ');

The problem with all this is that after the call you don't have any way of
finding out how many characters in a node's object contain valid data. I'd
suggest looking into using the type Ada.Strings.Unbounded.Unbounded_String
instead of String(1..1024).

--
T.E.D.

-----== Posted via Deja News, The Leader in Internet Discussion ==-----
http://www.dejanews.com/rg_mkgrp.xp   Create Your Own Free Member Forum