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Date: Fri, 24 Apr 1992 21:24:08 UTC+0100
From: Borja TORON ANTONS <toron@ccucvx.unican.es>
Subject: Oh, no! Ada-strings...
Message-ID: <182*/S=toron/OU=ccucvx/O=unican/PRMD=iris/ADMD=mensatex/C=es/@MHS>
List-Id: <comp.lang.ada>

Brian, 

the problem with ADA-strings is that range is too static. Your "empty string" 
is 0-length, but your variable 'str' is a 100-length string... 

they're different types for the compiler.

The solution is to use 'variable strings' as follows:

==================

Package Var_string is

   type vstring(len: natural:=200) is record
          str : STRING (1..len);
   end record;

   function "&" (s1,s2: in vstring) return vstring;
   function "&" (s1: in vstring; car : in CHARACTER) return vstring;
   function find (todo,sub_str: in vstring) return NATURAL;
   function copy (cadena: in vstring; index, count: in natural) return vstring;
   procedure delete(cadena: in out vstring; index, count: natural);
   function convert(s:string) return vstring;
   function "<" (iz,de: in vstring) return BOOLEAN;
   function ">" (iz,de: in vstring) return BOOLEAN;
end Var_string;


==================

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

==================

package body Var_string is

   function "&" (s1,s2: in vstring) return vstring is

   begin
        return (s1.len+s2.len,s1.str&s2.str);
   end "&";

   function "&" (s1: in vstring; car : in CHARACTER) return vstring is

   begin
        return (s1.len+1,s1.str&car);
   end "&";

   function find (todo,sub_str : in vstring) return NATURAL is

   begin
        for i in 1..todo.len-sub_str.len+1 loop
           if todo.str(i..i+sub_str.len-1)=sub_str.str then
                   return i;
           end if;
        end loop;
        return 0;
   end;

   function copy(cadena: in vstring; index, count: in natural) return vstring i
s
     s:vstring;
     indice:natural:=index;
   begin
      s:=(0,"");
      while (indice<=cadena.len)and(indice<=(index+count-1)) loop
	 s:=s&cadena.str(indice);
	 indice:=indice+1;
      end loop;
      return s;
   end;

   procedure delete(cadena: in out vstring; index, count: natural) is
      final: natural :=index+count;
      sub1, sub2: vstring;
   begin
      sub1:=(index-1, cadena.str(1..index-1));
      if final<cadena.len then
	 sub2:=(cadena.len-count, cadena.str(final..cadena.len));
	 cadena:=sub1&sub2;
      else
	 cadena:= sub1;
      end if;
   end;

   function "<" (iz,de: in vstring) return BOOLEAN is

   begin
        return iz.str<de.str;
   end "<";

   function ">" (iz,de: in vstring) return BOOLEAN is

   begin
        return iz.str>de.str;
   end ">";

   function convert(s:string) return vstring is
   begin
      return(s'last+1-s'first,s);
   end;

end Var_string;
=======================

with this package, if you have:

   str: vstring;

you could do:

   str:=(0,"");

or

   str:=convert("");

It's a bit longer, but it helps! 


Borja TORON
Just an ADA user...