哪位高手能介绍一个简单的api函数？

Private Declare Function mciSendString Lib "winmm.dll" Alias "mciSendStringA" ( _
ByVal lpstrCommand As String, ByVal lpstrReturnString As String, ByVal uReturnLength As Long, _
ByVal hwndCallback As Long) As Long

Dim Ret As Long
Dim RetStr As String
'打开
Ret = mciSendString("set CDAudio door open", RetStr, 0, 0)
'关闭
Ret = mciSendString("set CDAudio door closed", RetStr, 0, 0)
这个API的功能就是弹出和弹入光驱。