Memory management in Delphi[4]

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type 
  TForm1 =class (TForm)
    Button1: TButton;
    procedure Button1Click (Sender: TObject);
  end ;

var
  Form1: TForm1;

implementation

{$ R * .dfm}

var 
  MyHeap: THandle; {heap handle}
  p: Pointer;

procedure TForm1.Button1Click (Sender: TObject);
var
  i, num: Integer;
  p2: Pointer;
  str: string ;
begin
   {build heap}
  MyHeap: = HeapCreate (HEAP_ZERO_MEMORY, 1024*1024*2, 0); {Build a 2M heap}
  if Myheap =0 then Exit; { Exit if creation fails}

  {Allocate memory from the heap}
  p: = HeapAlloc (MyHeap, 0, 7);
  if p =nil then Exit; {exit on error}

  {Get memory block size}
  num: = HeapSize (MyHeap, 0, p);

  {Assign a value to each byte of a memory block}
  p2: = p;
  for i: =0 to num-1 do
  begin 
    Byte (p2 ^): = i +65;
    p2: = Ptr (Integer (p2) + 1);
  end ;

  {Value}
  p2: = p;
  str: = '';
  for i: =0 to num-1 do
  begin
    str: = str + Chr (Byte (p2 ^));
    p2: = Ptr (Integer (p2) + 1);
  end ;

  {Display the content and size of the memory block}
  ShowMessageFmt ('% s,% d', [str, num]); {ABCDEFG, 7}

  ///////////////////////////////////////////////////////// ///

  {Expand memory, only this sentence is different, the following are repeated the above code}
  p: = HeapReAlloc (MyHeap, 0, p, 26);
  if p =nil then Exit; {exit on error}

  {Get memory block size}
  num: = HeapSize (MyHeap, 0, p);

  {Assign a value to each byte of a memory block}
  p2: = p;
  for i: =0 to num-1 do
  begin 
    Byte (p2 ^): = i +65;
    p2: = Ptr (Integer (p2) + 1);
  end ;

  {Value}
  p2: = p;
  str: = '';
  for i: =0 to num-1 do
  begin
    str: = str + Chr (Byte (p2 ^));
    p2: = Ptr (Integer (p2) + 1);
  end ;

  {Display the content and size of the memory block}
  ShowMessageFmt ('% s,% d', [str, num]); {ABCDEFGHIJKLMNOPQRSTUVWXYZ, 26}

  ///////////////////////////////////////////////////////// ///

  {Free up memory}
  HeapFree (MyHeap, 0, p);

  {Destroy heap}
  HeapDestroy (MyHeap);
end ;

end .