Dll 文件:
--------------------------------------------------------------------------------

library Lib;

uses
SysUtils, Classes;

{$R *.res}

procedure Test(p: PChar);
const
Title = 'Title ';
var
str: string;
begin
str := p;
StrCopy(p, Title);
StrCat(p, PChar(str));
end;

exports Test;

begin
end.
--------------------------------------------------------------------------------
调用的代码文件:
--------------------------------------------------------------------------------

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}

procedure Test(p: PChar); external 'Lib.dll';

var num: Integer;

procedure TForm1.Button1Click(Sender: TObject);
var
p: PChar;
begin
Inc(num);
p := StrAlloc(255);
StrCopy(p, PChar(IntToStr(num)));
Test(p);
Text := p;
StrDispose(p);
end;

end.