Project Structure

• Callfrst.dpr
• CallForm.pas
• CallForm.dfm

program Callfrst;

uses
  ShareMem,
  Forms,
  CallForm in 'CallForm.pas' {Form1};

{$R *.RES}

begin
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

unit CallForm;

interface

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

type
  TForm1 = class(TForm)
    BtnDouble: TButton;
    SpinEdit1: TSpinEdit;
    Label1: TLabel;
    BtnTriple: TButton;
    Label2: TLabel;
    SpinEdit2: TSpinEdit;
    BtnDoubleString: TButton;
    BtnDoublePChar: TButton;
    EditSource: TEdit;
    EditDouble: TEdit;
    Label3: TLabel;
    Label4: TLabel;
    Bevel1: TBevel;
    Bevel2: TBevel;
    procedure BtnDoubleClick(Sender: TObject);
    procedure BtnTripleClick(Sender: TObject);
    procedure BtnDoubleStringClick(Sender: TObject);
    procedure BtnDoublePCharClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

{functions of the Delphi DLL}
function Double (N: Integer): Integer;
  stdcall; external 'FIRSTDLL.DLL';
function Triple (N: Integer): Integer;
  stdcall; external 'FIRSTDLL.DLL';
function DoubleString (S: string; Separator: Char): string;
  stdcall; external 'FIRSTDLL.DLL';
function DoublePChar (BufferIn, BufferOut: PChar;
  BufferOutLen: Cardinal; Separator: Char): LongBool;
  stdcall; external 'FIRSTDLL.DLL';

procedure TForm1.BtnDoubleClick(Sender: TObject);
begin
  SpinEdit1.Value := Double (SpinEdit1.Value);
end;

procedure TForm1.BtnTripleClick(Sender: TObject);
begin
  SpinEdit2.Value:= Triple (SpinEdit2.Value);
end;

procedure TForm1.BtnDoubleStringClick(Sender: TObject);
begin
  // call the DLL function directly
  EditDouble.Text :=
    DoubleString (EditSource.Text, ';');
end;

procedure TForm1.BtnDoublePCharClick(Sender: TObject);
var
  Buffer: string;
begin
  // make the buffer large enough
  SetLength (Buffer, 1000);
  // call the DLL function
  if DoublePChar (PChar (EditSource.Text), PChar (Buffer), 1000, '/') then
    EditDouble.Text := Buffer;
end;

end.

object Form1: TForm1
  Left = 250
  Top = 134
  Width = 352
  Height = 254
  Caption = 'Call Delphi DLL'
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clBlack
  Font.Height = -11
  Font.Name = 'MS Sans Serif'
  Font.Style = []
  OldCreateOrder = True
  PixelsPerInch = 96
  TextHeight = 13
  object Bevel1: TBevel
    Left = 8
    Top = 120
    Width = 321
    Height = 97
  end
  object Bevel2: TBevel
    Left = 8
    Top = 8
    Width = 321
    Height = 105
  end
  object Label1: TLabel
    Left = 152
    Top = 24
    Width = 30
    Height = 13
    Caption = 'Value:'
  end
  object Label2: TLabel
    Left = 152
    Top = 72
    Width = 30
    Height = 13
    Caption = 'Value:'
  end
  object Label3: TLabel
    Left = 149
    Top = 140
    Width = 37
    Height = 13
    Caption = 'Source:'
  end
  object Label4: TLabel
    Left = 152
    Top = 184
    Width = 37
    Height = 13
    Caption = 'Double:'
  end
  object BtnDouble: TButton
    Left = 32
    Top = 16
    Width = 89
    Height = 33
    Caption = 'Double'
    TabOrder = 0
    OnClick = BtnDoubleClick
  end
  object SpinEdit1: TSpinEdit
    Left = 192
    Top = 19
    Width = 81
    Height = 22
    MaxValue = 0
    MinValue = 0
    TabOrder = 1
    Value = 10
  end
  object BtnTriple: TButton
    Left = 32
    Top = 64
    Width = 89
    Height = 33
    Caption = 'Triple'
    TabOrder = 2
    OnClick = BtnTripleClick
  end
  object SpinEdit2: TSpinEdit
    Left = 192
    Top = 67
    Width = 81
    Height = 22
    MaxValue = 0
    MinValue = 0
    TabOrder = 3
    Value = 10
  end
  object BtnDoubleString: TButton
    Left = 32
    Top = 128
    Width = 89
    Height = 33
    Caption = 'Double String'
    TabOrder = 4
    OnClick = BtnDoubleStringClick
  end
  object BtnDoublePChar: TButton
    Left = 32
    Top = 176
    Width = 89
    Height = 33
    Caption = 'Double PChar'
    TabOrder = 5
    OnClick = BtnDoublePCharClick
  end
  object EditSource: TEdit
    Left = 195
    Top = 137
    Width = 121
    Height = 21
    TabOrder = 6
    Text = 'Hello, world'
  end
  object EditDouble: TEdit
    Left = 195
    Top = 180
    Width = 121
    Height = 21
    ReadOnly = True
    TabOrder = 7
    Text = '(result)'
  end
end