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From: "bubble" <bubble@riskm.com.tw>
Newsgroups: comp.lang.ada
Subject: Re: function "&" for strings type cause memory problem.
Date: Fri, 11 Nov 2005 16:25:21 +0800
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Date: 2005-11-11T16:25:21+08:00
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dear all:
thank your reply.
correct me if I'm wrong.


maybe the subject should be
 function "&"  crash in thread's stack size is too small, even if you have a 
big heap memory.

I knew to allocate a "large" object in stack is a bad idea.(another 
question:how to define "large"  to stack?)
and I allocate the large object in heap memory  in previous case.
It's seem so beauty :)

if "&" is  creating its result on the stack ,it still has potential risk.

in others.
I don't want to tell my programer:
" you can not use & for string or array,it has 1% probability to crash"

I want to say.
"  & for string or array merge don't crash, but you will get worst 
performace"
" you can change code and you will get better performance"


To Jeff and Dmitry.

in fact.
the the kernel(ada part) just crash "few" times.
It work perfectly until now after I change something like new test case .

my string are not so big,
I give you the extreme example.
because I just want to say bugs often happen in extreme case.
and I have not find any documents to increasing stack size in VB6.


please see new test case.

--------for test.adb-----------------------
with Ada.Text_IO;
Use Ada.Text_Io;
With stringFunctionPatch;

procedure test Is
   Type Access_String Is Access String;
   String1 : String := (1 .. 10_000_000 => 'a');
   String2 : String := (1 .. 10_000_000 => 'b');
   function "&" (Left,Right:string)Return String Renames 
StringFunctionPatch."&"; --enable/disable the line

begin
   declare
      Nstring2 : access_string := null;
   begin
      Nstring2 := new String'(String1 & String2);
      Put_Line("Test 2 Passed ");
   end;
end test;



---------------------stringFunctionPatch.ads-------------------
package stringFunctionPatch is
   Function  "&"(Left,Right:string)Return String;
end stringFunctionPatch;



--------------------stringFunctionPatch.adb-------------------
with Ada.Finalization;
With Ada.Unchecked_Deallocation;

package body stringFunctionPatch is
   type string_pointer is access String;
   Procedure  Free Is New Ada.Unchecked_Deallocation(String,String_Pointer);

   type Buffer is new Ada.Finalization.Controlled with record
      Data:string_pointer:=Null;
   end record;

   procedure Finalize   (Object : in out Buffer) Is
   Begin
      Free(Object.Data);
   End;

   function "&" (Left, Right : String) return String Is
      StringBuffer:Buffer;
   Begin
      Stringbuffer.Data:=New String (1 .. Left'Length + Right'Length);
      Stringbuffer.Data.all (1 .. left'Last) := left;
      Stringbuffer.Data.all ( Left'Last+1 .. Left'Last + Right'Last):=Right 
;
      return Stringbuffer.Data.all;
   end "&";

end stringFunctionPatch;