高手进来看看~~！！

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Private lCurLineNum As Long, lTotLines As Long, lLineLength
''Private Declare Function OSWinHelp% Lib "user32" Alias "WinHelpA" (ByVal hWnd&, ByVal HelpFile$, ByVal wCommand%, dwData As Any)
                                    '下面的是为了撤消过程用的 ！！！！！
Const EM_CANUNDO = &HC6
Private Declare Function SendMessageU Lib "user32" Alias _
    "SendMessageA" _
    (ByVal hwnd0 As Long, _
    ByVal wMsg0 As Long, _
    ByVal wParam0 As Long, _
    ByVal lParam0 As Long) As Long
    Const EM_UNDO = &HC7
                                      '撤消过程用的 ！！！！
'得 到 TEXTBOX中 第 N行 字 符
Private Declare Function SendMessage Lib "user32" _
     Alias "SendMessageA" _
     (ByVal hWnd As Long, _
     ByVal wMsg As Long, _
     ByVal wParam As Long, _
     ByVal lParam As String) _
     As Long
   
Private Declare Function lstrlen Lib "kernel32" Alias "lstrlenA" (ByVal lpString As String) As Long
    '' Private Const EM_GETLINE = &HC4
     Private Const EM_GETLINECOUNT = &HBA
     Private Const EM_GETSEL = &HB0
     Private Const EM_LINEFROMCHAR = &HC9
    '' Private Const EM_LINEINDEX = &HBB
    '' Private Const EM_LINELENGTH = &HC1
     Private Const EM_REPLACESEL = &HC2




Private Sub EditUndo_Click()
   SendMessageU RichTextBox1.hWnd, EM_UNDO, 0&, 0&
End Sub