What happens when AnsiString is cast to PAnsiString?

Question

I have the method (Delphi 2009):

procedure TAnsiStringType.SetData(const Value: TBuffer; IsNull: boolean = False);
begin
  if not IsNull then
    FValue:= PAnsiS         


        

Answer 1

Nice puzzle, but I have the solution:

• P2 and P3 are the address of the pointer to the buffer
• P1 and P4 are the address of the buffer
• P5 is the first element in the buffer

I have added comment in the code:

var
  Buffer: AnsiString;
  P1: Pointer;
  P2: Pointer;
  P3: Pointer;
  P4: Pointer;
  P5: Pointer;
begin
  P1:= PAnsiString(Buffer); 
  (* A cast from AnsiString to PAnsiString has no real meaning 
     because both are a pointer to a block of characters ()
  P2:= Addr(Buffer);
  P3:= @Buffer;
  (* Both Addr and @ give the address of a variable. The variable Buffer is 
     a pointer so we get the address of the pointer, not the value of the 
     pointer. *)
  P4:= Pointer(Buffer);
  (* See the remark on P1. Due to the cast both give the same result. *)
  P5:= PChar(Buffer[1]);
  (* This looks like a pointer to the first element. But the cast changes 
     it into the character. *)
  WriteLn('P1: ' + IntToStr(Integer(P1)));
  WriteLn('P2: ' + IntToStr(Integer(P2)));
  WriteLn('P3: ' + IntToStr(Integer(P3)));
  WriteLn('P4: ' + IntToStr(Integer(P4)));
  WriteLn('P5: ' + IntToStr(Integer(P5)));
end;