Private Declare Function SendMessage Lib "user32" _
  Alias "SendMessageA" (ByVal hwnd As Long, _
  ByVal wMsg As Long, ByVal wParam As Long, _
  ByVal lParam As Any) As Long
 
Private Const EM_GETLINE = &HC4
Private Const EM_GETLINECOUNT = &HBA
 
Public Function tbGetLine(ByVal hWnd As Long, _
  ByVal nLine As Long) As String
 
  Dim nLineCount As Long
  Dim nLen As Long
  Dim sLine As String
 
  ' zunächst die Anzahl der Zeilen ermitteln
  nLineCount = SendMessage(hwnd, EM_GETLINECOUNT, 0, 0&)
 
  If nLine > 0 And nLine <= nLineCount Then
    ' Jetzt Zeile auslesen
    sLine = Space$(1024)
    nLen = SendMessage(hwnd, EM_GETLINE, nLine - 1, sLine) ' <<< hier Fehler 
    ' und Abbruch
 
    tbGetLine = Left$(sLine, nLen)
  Else
    ' Ungültiger Zeilen-Index
    tbGetLine = vbNullString
  End If
End Function
 
Private Sub Command1_Click()
Dim sLine As String
 
' 1. Zeile ermitteln und auslesen
sLine = tbGetLine(Text1.hWnd, 1)
 
End Sub
 
Private Sub Form_Load()
' TextBox füllen (MultiLine = True)
Text1.Text = "123456789012345678901234567890123456789012345678901234567890"
End Sub