String Copy Internals

Asked Oct 05 '15 at 07:44

Active Oct 05 '15 at 07:44

Viewed 44 times

Consider this code:

program Project11;

{$APPTYPE CONSOLE}

uses
  SysUtils;

function Test: string;
var
   r, s: string;
begin
   r := 'Hello';
   Writeln(Format('%.8x', [NativeInt(Pointer(r))]));
   s := r;
   Writeln(Format('%.8x', [NativeInt(Pointer(s))]));
   Result := r;
   Writeln(Format('%.8x', [NativeInt(Pointer(Result))]));
end;

var
  S1: string;

begin
  try
    S1:= Test;
    Writeln(Format('%.8x', [NativeInt(Pointer(S1))]));
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
  Readln;
end.

When running it on Delphi XE I get

0040F358
0040F358
020A28CC
020A28CC

The question: why the compiler makes a deep copy when assigning a local string variable to the function's result?

asked Oct 05 '15 at 07:44

kludg

27,213
5
67
118

Good question. Arnuad's answer at the dupe is excellent. It would be really great if somebody could cast the final delete vote on the erroneous accepted answer there..... – David Heffernan Oct 05 '15 at 07:55
Well it turns out that the reason is the string literal used in the function's code; no literal, no deep copy. – kludg Oct 05 '15 at 08:11
Which is what Arnaud said – David Heffernan Oct 05 '15 at 08:12

String Copy Internals

0 Answers0