For each item, the program sends the control the LB_GETTEXTLEN message to get the item's length. It allocates space in a string for the item and then sends the LB_GETTEXT message to copy the item into the string. Notice that the program then uses the Left$ function to get the item's text. This removes the trailing Null character from the string.

Private Sub Command1_Click()
Dim num As Long
Dim i As Integer
Dim txt As String
Dim entry As String
Dim length As Long

    ' See how many entries the list has.
    num = SendMessage(List1.hwnd, LB_GETCOUNT, 0, 0)
    
    ' Read each entry.
    For i = 0 To num - 1
        ' See how long the entry is.
        length = SendMessage(List1.hwnd, LB_GETTEXTLEN, i, _
            0)
        
        ' Make entry big enough.
        entry = Space$(length + 1)

        ' Get the entry.
        length = SendMessage(List1.hwnd, LB_GETTEXT, i, _
            ByVal entry)
        txt = txt & Left$(entry, length) & vbCrLf
    Next i
    
    MsgBox txt
End Sub