<font color=green>' zunächst die benötigten API-Deklarationen</font>
Private Declare Function OpenFile Lib "kernel32" (ByVal lpFileName As String, _
  lpReOpenBuff As Any, ByVal wStyle As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As _
  Long
Private Declare Function GetFileSizeA Lib "kernel32.dll" Alias "GetFileSize" _
  (ByVal hFile As Long, lpFileSizeHigh As Long) As Long
 
Private Const OFS_MAXPATHNAME = 128
 
Private Type OFSTRUCT
  cBytes As Byte
  fFixedDisk As Byte
  nErrCode As Integer
  Reserved1 As Integer
  Reserved2 As Integer
  szPathName As String * OFS_MAXPATHNAME
End Type

<font color=green>' Dateigröße einer lokalen Datei ermitteln</font>
Private Function GetLocalFileSize(ByVal FileName As String) As Long
  Dim Retval As Long
  Dim hFile As Long
  Dim SizeLng As Long
  Dim OF As OFSTRUCT
 
  <font color=green>' Datei öffnen</font>
  hFile = OpenFile(FileName, OF, 0&)
  If hFile = -1 Then
    <font color=green>' Datei existiert nicht!</font>
    GetLocalFileSize = -1
    Exit Function
  End If
 
  <font color=green>' Göße ermitteln und Datei schließen</font>
  GetLocalFileSize = GetFileSizeA(hFile, SizeLng)
  CloseHandle hFile
End Function