如何获取本机当前登陆的QQ号码

Private Function GetQQ() As String
    Dim i As Long
    Dim cls As Long
    Dim hWin As Long
    Dim szTmp As String
    Dim l As Long
   
    cls = &H61A00000
   
    For i = 0 To 17
        cls = cls + &H10000
        Do
            hWin = FindWindowEx(0, hWin, "Afx:" & Hex(cls) & ":2", vbNullString) 'ws的qq，用版本号当做类名。。。
            szTmp = String(260, vbNullChar)
            Call GetWindowText(hWin, szTmp, 260)
            szTmp = Left$(szTmp, GetWindowTextLength(hWin))
            l = InStr(szTmp, "_QQMusic_SmallClient")
            If l > 0 Then
                GetQQ = Left$(szTmp, l - 1)
                Exit Function
            End If
            If hWin = 0 Then Exit Do
        Loop
    Next
End Function
为什么得到的是“”空值