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Date: Fri, 4 Dec 2015 07:49:28 -0800 (PST)
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Subject: Problem with Unbounded Strings
From: Laurent <lutgenl@icloud.com>
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Xref: news.eternal-september.org comp.lang.ada:28631
Date: 2015-12-04T07:49:28-08:00
List-Id: <comp.lang.ada>

Hi

I have a problem with unbounded strings. When I append a String(1..10) to my Buffer which is an unbounded string it works. 

So my Buffer has the length 10. 

If I use this buffer of length 10 and append again a String(1..10) the length of the buffer should increase to 20 and I should have the content of both strings?

Somehow in the procedure I have written that doesn't happen. The Buffer seems to get fixed to the length of the first string and further appending doesn't change it. The new string gets appended but truncated at its begin and the buffer at the end.

I have no idea why that happens. I suppose something silly as always.

There is no difference between using append or "&". The behaviour is the same.

If someone could enlighten me I would be happy. 

Thanks

Laurent

   package U_B renames Ada.Strings.Unbounded;
   subtype Ub_S is U_B.Unbounded_String;

  function "+" (Right : U_B.Unbounded_String) return String
                 renames U_B.To_String;

   function "+" (Right : String) return U_B.Unbounded_String
   is (U_B.To_Unbounded_String (Right));

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

procedure Read_Message (File         : in Ada.Text_IO.File_Type;
                                           Buffer       : out Ub_S;
                                      Has_Finished : out Boolean)
   is
   begin -- Read_Message
      Has_Finished := False;
      Buffer := +"";

      while not Ada.Text_IO.End_Of_File (Log_File) loop
         declare
            S     : String := Ada.Text_IO.Get_Line (File => File);
            Line : String (1 .. S'Length - TStamp);
            -- removes this useless timestamp

         begin -- declare

            Line (1 .. Line'Last) := S (38 .. S'Last);
            
            if Line (1 .. 5) = EOT then
               -- we have reached the end of the message so we can exit the loop
               -- and hand over the Buffer for treatment
               -- Has_Finished has to be set to True

               Has_Finished := True;
               exit; -- end of message

            elsif Line (1 .. 5) = ETX
              or Line (1 .. 5) = ACK
              or Line (1 .. 5) = ENQ
              or Line (1 .. 5) = STX
              or Line (1 .. 4) = GS
            -- if Line contains ETX, ACK, ENQ, STX or GS commands,
            -- we don't need them, so just ignore
            then
               null;

            elsif Line (1 .. 4) = RS then
               -- so Line contains RS command which indicates the begin of
               -- a message so we have to take care of those lines

                 U_B.Append (Source   => Buffer,
                            New_Item => Line (5 .. Line'Last));

               -- Buffer := U_B."&" (Buffer,Line ( 5 .. Line'Last));

            else
               -- Line is something else, like some info about the succes of
               -- the backup engine. who cares?
               null;
            end if;
         end;
      end loop;
   end Read_Message;