Delphi内でDLLを記述して呼び出す方法

次のコードは、2つの整数のうち大きい方を返す目的で、MinとMaxの2つの関数を含むDLLを作成します。

Delphiで新しいDLLプロジェクトを開始します（[ファイル]→ [新規]をクリックし、DLLを選択します）。
プロジェクトをdelhpdllとして保存します。
以下に示すように、ライブラリにコードを入力します。

//Uffe wrote: This is a toy dll to demonstrate the
//use of dll's
//
//The libary export two functions Max and Min
//
//The dll matches the MainProject which is a Delphi
//project which calls the DLL.

//{
//  DELPHI WROTE THIS:
//  Important note about DLL memory management: ShareMem
//  must be the first unit in your library's USES clause
//  AND your project's (select Project-View Source) USES
//  clause if your DLL exports any procedures or functions
//  that pass strings as parameters or function results.
//  This applies to all strings passed to and from your
//  DLL--even those that are nested in records and classes.
//  ShareMem is the interface unit to the BORLNDMM.DLL
//  shared memory manager, which must be deployed along
//  with your DLL. To avoid using BORLNDMM.DLL, pass
//  string information using PChar or ShortString
//  parameters.
//}

uses
   SysUtils,
   Classes;

//Declare stdcall to make interface to other languages

function Min(X, Y: Integer): Integer; stdcall;
begin
   if X < Y then Min := X else Min := Y;
end;

function Max(X, Y: Integer): Integer; stdcall;
begin
   if X > Y then Max := X else Max := Y;
end;

exports//Make available to calling applications
   Min index 1,
   Max index 2;

begin
end.

DLLプロジェクトをビルドして保存します。

（コマンドラインのような人なら、コマンドラインから「dcc32 delhpdll.dpr」を実行するだけで… それはあなたに同じDLLを与えるでしょうが、IDEのものなしで…）。

次に、DLLを呼び出すためのアプリケーションが必要です。

新しい「メイン」アプリケーションプロジェクトを開始します。
DLLのテストに必要なGUIコントロールを作成します。 *以下に示すように、DLLをインターフェースするためのソースコードを入力します。

//Main Applet to demonstrate how to call a dll.
//

//SEARCH PATHS:
//  The code makes no special effort to search for the DLL.
//  Easiest if everything (including DLL) is in the same
//  directory.
//

//DLL CALLING:
//  This applet demonstrates both Win API calling and
//  external calling (see below)
//
//

//NOTICE: I wasted a lot of time not declaring the
//functions "stdcall" throughout. If you
//declare it "stdcall" in the DLL and not
//in the calling application, then you get hard-to-find
//errors - "external" will crash on you,
//the Win API does not type-check so the function
//just gives "weird" results. (OK this is
//obvious when you think about it .. problem is,
//I didn't)

//Jump to "implementation" section,
//no DLL specs before.
interface

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

type
   TForm1 = class(TForm)

   Edit1: TEdit;
   Edit2: TEdit;

   Button1: TButton;
   Label1: TLabel;
   Label2: TLabel;

   Button2: TButton;
   Label3: TLabel;
   Label4: TLabel;
   Label5: TLabel;

   procedure Button1Click(Sender: TObject);
   procedure Button2Click(Sender: TObject);

   private
   { Private declarations }

   public
   { Public declarations }
   end;

  //TMaxFun becomes a function variable (think of
  //a "pointer to function" without the pointer)

   TMaxFun = function(i,j: integer):integer; stdcall;

var
   Form1: TForm1;

implementation

{$R* .DFM}

//This declares Max as a function which should be found
//externally, in the dll
function Max(i,j:integer): integer;  stdcall; external 'delhpdll.dll';

//This procedure uses the "external" call to the DLL
   procedure TForm1.Button1Click(Sender: TObject);
var
   i,j: integer;

begin
   i := strtoint(Edit1.Text);
   j := strtoint(Edit2.Text);

   Label1.Caption := inttostr(Max(i,j));
  //Easy, eh?
end;

//This calls the DLL directly through the Win API.
//More code, more control.

procedure TForm1.Button2Click(Sender: TObject);
var
   i,j,k: integer;
   Handle: THandle;

  //mmax is a function variable; see type declaration
  //of TMaxFun above.
   mmax : TMaxFun;

begin
   i := strtoint(Edit1.Text);
   j := strtoint(Edit2.Text);

  //Load the library
   Handle := LoadLibrary('DELHPDLL.DLL');

  //If succesful ...

   if Handle <> 0 then
      begin

     //Assign function Max from the DLL to the
     //function variable mmax

      @mmax := GetProcAddress(Handle, 'Max');

     //If successful

      if @mmax <> nil then
         begin
            k := mmax(i,j);
            Label1.Caption := inttostr(k);
         end;

     //Unload library
      FreeLibrary(Handle);
   end;
end;
end.

行って、飛んで、プログラムを実行してください。

Dll-delphi-example

Delphi内でDLLを記述して呼び出す方法