library TestDLL;

{ 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;

function ADD(X,Y:Integer):Integer;stdcall;

begin

  Result :=X+Y;

end;

function Txx(x,y:Double):Double ;stdcall ;

begin

  Result :=x+y+y+x;

end;

function EncryVncPassStrHex(Str: PChar): PChar;stdcall;

var

  TempResult: String;

begin

  TempResult := WideCharToString(str);

  Result := PChar(TempResult);

end;

{$R *.res}

exports

   ADD,

   EncryVncPassStrHex,

   Txx;

begin

end.

using System;

using System.Collections.Generic;

using System.Drawing;

using System.Windows.Forms;

using System.Runtime.InteropServices;

namespace UseDLL

{

    /// <summary>

    /// Description of MainForm.

    /// </summary>

    public class UseDLL

    {

        [DllImport("TestDLL.DLL",EntryPoint="ADD",CharSet= CharSet.Auto,CallingConvention=CallingConvention.StdCall)]

        public static extern int add(int x,int y);

        [DllImport("TestDLL.DLL",EntryPoint="Txx",CharSet= CharSet.Auto,CallingConvention=CallingConvention.StdCall)]

        public static extern double PP(double x,double y);

        [DllImport("TestDLL.DLL", EntryPoint="EncryVncPassStrHex",CharSet=CharSet.Auto, CallingConvention = CallingConvention.StdCall)]

         public static extern string EncryVncPassStrHex( string Str);

    }

    public partial class MainForm : Form

    {

        public MainForm()

        {

            //

            // The InitializeComponent() call is required for Windows Forms designer support.

            //

            InitializeComponent();

            //

            // TODO: Add constructor code after the InitializeComponent() call.

            //

        }

        void Button1Click(object sender, EventArgs e)

        {

            int x=;

            int y=;

            int z=UseDLL.add(x,y);

            this.textBox1.Text=z.ToString();

            double oo=0.123;

            double pp=0.254;

            this.button1.Text=UseDLL.PP(oo,pp).ToString();

            this.Text =UseDLL.EncryVncPassStrHex("我是XXX");

        }

    }

}