利用COPYDATASTRUCT传递命令行参数给驻留内存的进程（SendMessage应用）

我们知道Window进程之间通过API的SendMessage方法传递消息。但是方法参数lParam是Long型，那么如果传递一个字符串（譬如命令行参数）应该怎么办呢，甚至一个对象、结构呢。VB的发送接收需要通过传递指针实现（换言之是字符串的内存地址），下面总结VB方式、C#方式各自如何实现消息的发送与接收；各自是可以互换的，譬如C#发送的消息，VB窗口可以收到；相反亦可以。当然同种语言之间更加没问题了。

VB发送端 Form1.frm：

 Option Explicit

 Private Type COPYDATASTRUCT
     dwData As Long
     cbData As Long
     lpData As Long
 End Type

 Private Const WM_COPYDATA = &H4A

 Private Declare Function FindWindow Lib "user32" Alias _
    "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName _
    As String) As Long

 Private Declare Function SendMessage Lib "user32" Alias _
    "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal _
    wParam As Long, lParam As Any) As Long

 'Copies a block of memory from one location to another.
 Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
    (hpvDest As Any, hpvSource As Any, ByVal cbCopy As Long)

 Private Sub Command1_Click()
     Dim cds As COPYDATASTRUCT
     Dim ThWnd As Long
     Dim buf( To ) As Byte
     Dim a As String, i As Long, lLen As Long

     ' Get the hWnd of the target application
     ThWnd = FindWindow(vbNullString, "Target")
     a$ = "It Works on " & Format(Now, "yyyy-MM-dd HH:mm:ss") & " !"
     ' Copy the string into a byte array, converting it to ASCII
     lLen = LenB(StrConv(a, vbFromUnicode))
     Call CopyMemory(buf(), ByVal a, lLen)
     cds.dwData =
     cds.cbData = lLen +
     cds.lpData = VarPtr(buf())
     i = SendMessage(ThWnd, WM_COPYDATA, Me.hwnd, cds)
 End Sub

 Private Sub Form_Load()
     ' This gives you visibility that the target app is running
     ' and you are pointing to the correct hWnd
     Me.Caption = Hex$(FindWindow(vbNullString, "Target"))
 End Sub

VB接收端

1。MsgHook.bas：

 Option Explicit

 Type COPYDATASTRUCT
     dwData As Long
     cbData As Long
     lpData As Long
 End Type

 Public Const GWL_WNDPROC = (-)
 Public Const WM_COPYDATA = &H4A
 Global lpPrevWndProc As Long
 Global gHW As Long

 'Copies a block of memory from one location to another.
 Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
    (hpvDest As Any, hpvSource As Any, ByVal cbCopy As Long)

 Declare Function CallWindowProc Lib "user32" Alias _
    "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hwnd As _
    Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As _
    Long) As Long

 Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" _
    (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As _
    Long) As Long

 Public Sub Hook()
     lpPrevWndProc = SetWindowLong(gHW, GWL_WNDPROC, _
     AddressOf WindowProc)
     Debug.Print lpPrevWndProc
 End Sub

 Public Sub Unhook()
     Dim temp As Long
     temp = SetWindowLong(gHW, GWL_WNDPROC, lpPrevWndProc)
 End Sub

 Function WindowProc(ByVal hw As Long, ByVal uMsg As Long, _
    ByVal wParam As Long, ByVal lParam As Long) As Long
     If uMsg = WM_COPYDATA Then
         Call mySub(lParam)
     End If
     WindowProc = CallWindowProc(lpPrevWndProc, hw, uMsg, wParam, lParam)
 End Function

 Sub mySub(lParam As Long)
     Dim cds As COPYDATASTRUCT
     Dim buf( To ) As Byte
     Dim a As String

     Call CopyMemory(cds, ByVal lParam, Len(cds))

     Select Case cds.dwData
      Case
         Debug.Print "got a 1"
      Case
         Debug.Print "got a 2"
      Case
         Call CopyMemory(buf(), ByVal cds.lpData, cds.cbData)
         a$ = StrConv(buf, vbUnicode)
         a$ = Left$(a$, InStr(, a$, Chr$()) - )
         Form1.Label1.Caption = a$
     End Select
 End Sub

2。Target.frm：

 Option Explicit

 Private Sub Form_Load()
     gHW = Me.hwnd
     Hook
     Me.Caption = "Target"
     Me.Show
     Label1.Caption = Hex$(gHW)
 End Sub

 Private Sub Form_Unload(Cancel As Integer)
     Unhook
 End Sub

C#的发送端：

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Windows;
 using System.Windows.Controls;
 using System.Windows.Data;
 using System.Windows.Documents;
 using System.Windows.Input;
 using System.Windows.Media;
 using System.Windows.Media.Imaging;
 using System.Windows.Navigation;
 using System.Windows.Shapes;
 using System.Runtime.InteropServices;

 namespace CSMsgSender
 {
     /// <summary>
     /// MainWindow.xaml 的交互逻辑
     /// </summary>
     public partial class MainWindow : Window
     {
         public MainWindow()
         {
             InitializeComponent();
         }

         private void button1_Click(object sender, RoutedEventArgs e)
         {
             int hwnd = FindWindow(null, "Target");
             if (hwnd != )
             {
                 string str = "It Works on " + DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") + " !";
                 byte[] arr = System.Text.Encoding.Default.GetBytes(str);
                 int len = arr.Length;
                 COPYDATASTRUCT cdata;
                 cdata.dwData = ;
                 cdata.lpData = str;
                 cdata.cbData = len + ;
                 SendMessage(hwnd, WM_COPYDATA, , ref cdata);
             }
         }

         [DllImport("User32.dll")]
         public static extern int SendMessage(int hwnd, int msg, int wParam, ref COPYDATASTRUCT lParam);
         [DllImport("User32.dll")]
         public static extern int FindWindow(string lpClassName, string lpWindowName);

         private const int WM_COPYDATA = 0x004A;
         public struct COPYDATASTRUCT
         {
             public int dwData;
             public int cbData;
             [MarshalAs(UnmanagedType.LPStr)]
             public string lpData;
         }
     }
 }

C#接收端：

 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Data;
 using System.Drawing;
 using System.Linq;
 using System.Text;
 using System.Windows.Forms;
 using System.Runtime.InteropServices;

 namespace CSMsgReceiver
 {
     public partial class Form1 : Form
     {
         public Form1()
         {
             InitializeComponent();
             this.Text = "Target";
         }

         protected override void DefWndProc(ref Message m)
         {
             switch (m.Msg)
             {
                 case WM_COPYDATA:
                     COPYDATASTRUCT cdata = new COPYDATASTRUCT();
                     Type mytype = cdata.GetType();
                     cdata = (COPYDATASTRUCT)m.GetLParam(mytype);
                     this.textBox1.Text = cdata.lpData;
                     break;
                 default:
                     base.DefWndProc(ref m);
                     break;
             }
         }

         //WM_COPYDATA消息的主要目的是允许在进程间传递只读数据。
         private const int WM_COPYDATA = 0x004A;

         //Windows在通过WM_COPYDATA消息传递期间，不提供继承同步方式。
         //其中,WM_COPYDATA对应的十六进制数为0x004A
         public struct COPYDATASTRUCT
         {
             public int dwData;
             public int cbData;
             [MarshalAs(UnmanagedType.LPStr)]
             public string lpData;
         }
     }
 }