Динамическая и статическая загрузка DLL

{Project file name: c:\example\exdouble\exdouble.dpr}

library ExDouble;
// my simple dll

function calc_double(r: real): real; stdcall;
begin
  result := r * 2;
end;

exports
  calc_double index 1;

end;

unit untMain;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
end;

var
  Form1: TForm1;

implementation

function calc_double(r: real): real; stdcall; external 'ExDouble.dll';

{$R *.DFM}

procedure TForm1.Button1Click(Sender: TObject);
begin
  // в окошке сообщения будет цифра 21
  ShowMessage(FloatToStr(calc_double(10.5)));
end; 

end.

unit untMain;

interface

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

type
  Tcalc_double = function ( r: real ): real;

  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.Button1Click(Sender: TObject);
var
  hndDLLHandle: THandle;
  calc_double: Tcalc_double;
begin
  try
    // загружаем dll динамически
    hndDLLHandle := loadLibrary ( 'ExDouble.dll' );

    if hndDLLHandle <> 0 then
    begin

      // получаем адрес функции
      @calc_double := getProcAddress ( hndDLLHandle, 'calc_double' );

      // если адрес функции найден
      if addr ( calc_double ) <> nil then
      begin
        // показываем результат ( 21...)
        showMessage ( floatToStr ( calc_double ( 10.5 ) ) );
      end
      else
        // DLL не найдена ("handleable")
        showMessage ( 'Function not exists...' );

    end
    else
      // DLL не найдена ("handleable")
      showMessage ( 'DLL not found...' );

  finally
    // liberar
    freeLibrary ( hndDLLHandle );
  end;
end;

end.