Related:  

If you are using Windows 2000 or later, IsNetDrive can be used to determine whether a particular drive is mapped to a share and the connection state.  The value passed to IsNetDrive is not the drive letter to check, but rather an integer that indicates which drive letter you want to test, i.e. 0 for A:, 1 for B:, 2 for C:, and so on.

IsNetDrive returns 0 if the drive specified is not a network drive, 1 if the specified drive is a network drive that is properly connected to the network, or 2 if the specified drive is a network drive that is disconnected or in an error state.

In testing, I've determined that the state returned by this API reflects the success or failure of Windows to reconnect to shares when Windows boots up (session logon), or reflects the state of new mapped  or disconnected drives during the session. It can not be used as a test to ensure that a successful connection to a particular drive exists at a specific point in time (is still valid).  If all drives were successfully reconnected at boot then calls to this API return the state of the drives at logon. Drives that were mapped or disconnected by the user during the session are properly reflected as a change in state (e.g. from 1 or 2 to 0, or from 0 to 1). In other words, if you have a successful map and then turn off the server or network card, Windows still shows the connection state as 1 (properly connected).  While this may limit the use of this API as a test to ensure that a connection is valid before reading from or writing to a mapped share, the return value of 1 at least indicates that the share was valid at boot and correspondingly, a value of 2 indicates that Windows was unable to reattach the share and has been unsuccessful since.

The illustration shows that my mapped drives P: and Z: were successfully restored to the server when I logged on (values=1), while drive X was not successfully reconnected (value=2) as that server was off.

Option Explicit

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Private Declare Function IsNetDrive Lib "shell32" _
  (ByVal iDrive As Long) As Long


Private Sub Form_Load()

   Command1.Caption = "IsNetDrive"
   
End Sub


Private Sub Command1_Click()

   Dim cnt As Long
   
   List1.Clear
   
   For cnt = 0 To 25
      List1.AddItem Chr$(65 + cnt) & ":" & vbTab & IsNetDrive(cnt)
   Next
   
End Sub