调用 sendmessage 函数后的小问题

Option Explicit
Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByRef lParam As Any) As Long
Private Const EM_GETLINE As Long = &HC4
Private Const EM_GETLINECOUNT As Long = &HBA

Private Declare Sub CopyMemory Lib "kernel32.dll" Alias "RtlMoveMemory" (ByRef Destination As Any, ByRef Source As Any, ByVal length As Long)


Private Sub Form_Load()
Dim n As Integer
Text1.Text = vbNullString
For n = 0 To 19
Text1.Text = Text1.Text & "这是第" & Str(n + 1) & "行，I like vb6 very much." & vbCrLf
Next
End Sub

Private Sub GetLine_Click()
Dim S As String
Dim length As Integer
length = 40
S = Space(length)
CopyMemory ByVal S, length, 2 '传递前，S的前2个字节保存需获取字符串的长度
SendMessage Text1.hwnd, EM_GETLINE, 5, ByVal S '读取第六行的内容
Print S
Print "chr(0)的位置是 ", InStr(S, Chr(0))
End Sub

Private Sub LineCount_Click()
Dim count As Long
count = SendMessage(Text1.hwnd, EM_GETLINECOUNT, 0, ByVal 0&)
Print "一共", count - 1, "行"
End Sub