Private Shared Function SearchMidString(ByVal s As String, ByVal s1 As String, ByVal s2 As String) As String
        '获取搜索到的数目  
        Dim n1 As Integer, n2 As Integer
        n1 = s.IndexOf(s1, 0) + s1.Length
        '开始位置  
        n2 = s.IndexOf(s2, n1)
        '结束位置  
        Return s.Substring(n1, n2 - n1)
        '取搜索的条数，用结束的位置-开始的位置,并返回  
    End Function

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        'MsgBox(GetFileName("/dir1001/aaa.txt"))
        MsgBox(SearchMidString("/dir1001/ghghjghj/aaa.txt", "/", "/"))
    End Sub