Private Declare Function DeleteFile Lib "kernel32" Alias "DeleteFileA" (ByVal lpFileName As String) As Long
Private Declare Function GetShortPathName Lib "kernel32" Alias "GetShortPathNameA" (ByVal lpszLongPath As String, ByVal lpszShortPath As String, ByVal lBuffer As Long) As  Long
Private Declare Function MakeSureDirectoryPathExists Lib  "imagehlp.dll" (ByVal lpPath As String) As Long
'
Function GetShortPath(ByVal sFile As String, Optional bCreate As Boolean = False)  As String
    If bCreate Then
        Call MakeSureDirectoryPathExists(Left$(sFile, InStrRev(sFile, "\")))
        Dim FF As Integer: FF = FreeFile
        Open sFile For Output As #FF
            Print #FF, vbNullString
        Close #FF
        DoEvents
    End If
    
    Dim lRet As Long
    GetShortPath = String(1024, Chr$(0))
    lRet = GetShortPathName(sFile, GetShortPath, Len(GetShortPath))
    GetShortPath = Left$(GetShortPath, lRet)
    
    If bCreate Then Call DeleteFile(sFile)
End Function
'
' ========
' EXEMPLE
' ========
'
MsgBox Environ$("PROGRAMFILES") & "\outlook express\un fichier au hasard.txt" & vbCrLf & _
        GetShortPath(Environ$("PROGRAMFILES") & "\outlook express\un fichier  au  hasard.txt", True)

Shared Function GetShortPathName_CreateDestroy(ByVal Path As String) As String
  Dim fCreate As Boolean = Not System.IO.File.Exists(Path)
  If fCreate Then System.IO.File.Create(Path).Dispose()
  Dim shortPath As String = GetShortPathName(Path)
  If fCreate Then System.IO.File.Delete(Path)
  Return shortPath
End Function
Shared Function GetShortPathName(ByVal Path As String) As String
  Dim shortPath As New System.Text.StringBuilder(255)
  GetShortPathName(Path, shortPath, shortPath.Capacity)
  Return shortPath.ToString()
End Function
<System.Runtime.InteropServices.DllImport("kernel32.dll", SetLastError:=True, _
  CharSet:=System.Runtime.InteropServices.CharSet.Auto)> _
Private Shared Function GetShortPathName(ByVal Path As String, _
  ByVal ShortPath As System.Text.StringBuilder, _
  ByVal ShortPathLength As Integer) As Integer
End Function

[System.Runtime.InteropServices.DllImport("kernel32.dll", CharSet=System.Runtime.InteropServices.CharSet.Auto)]

private static extern int GetShortPathName(
  string Path,
  System.Text.StringBuilder ShortPath,
  int ShortPathLength
);

public static string GetShortPathName_CreateDestroy(string Path) {
  bool fCreate = !System.IO.File.Exists(Path);
  if (fCreate)
    System.IO.File.Create(Path).Dispose();
  string shortPath = GetShortPathName(Path);
  if (fCreate)
    System.IO.File.Delete(Path);
  return shortPath;
}

public static string GetShortPathName(string Path) {
  System.Text.StringBuilder shortPath = new System.Text.StringBuilder(255);
  GetShortPathName(Path, shortPath, shortPath.Capacity);
  return shortPath.ToString();
}