HOWTO: List Local Network Connections with WNetEnumResources

• Microsoft Visual Basic Professional and Enterprise Editions for Windows, versions 4.0, 5.0, 6.0
• Microsoft Windows NT versions 3.51, 4.0
• Microsoft Windows 95
• Microsoft Win32 Software Development Kit (SDK)

SUMMARY

WNetOpenEnum and WNetEnumResources can be used to list the local drives, printer ports that have been redirected, and any UNC connections on a machine running Windows NT, Windows 95, or Windows 98.

The code below demonstrates how to do this from Visual Basic by first calling WNetOpenEnum with the dwType parameter set to RESOURCETYPE_ANY. A valid handle returned via the last parameter is passed to WNetEnumResources. This function fills a temporary buffer with an array of NETRESOURCE structures, which includes information about the local network connections.

Note that this functionality will not list the resources that are redirected on a remote machine. No such functionality exists in either operating system.

MORE INFORMATION

The sample includes one form and one module. Follow the steps below to create the sample.

1. Create a new project and add the following code to the form:

   
         Option Explicit
   
         Private Const GMEM_FIXED = &H0
         Private Const GMEM_ZEROINIT = &H40
         Private Const GPTR = (GMEM_FIXED Or GMEM_ZEROINIT)
   
         Private Declare Function GlobalAlloc Lib "KERNEL32" ( _
            ByVal wFlags As Long, ByVal dwBytes As Long) As Long
         Private Declare Function GlobalFree Lib "KERNEL32" ( _
            ByVal hMem As Long) As Long
   
         Private Declare Sub CopyMemory Lib "KERNEL32" Alias "RtlMoveMemory" _
           (hpvDest As Any, hpvSource As Any, ByVal cbCopy As Long)
   
         Private Declare Function CopyPointer2String Lib "KERNEL32" _
            Alias "lstrcpyA" ( _
            ByVal NewString As String, ByVal OldString As Long) As Long
   
         Private Sub Form_click()
            Dim hEnum As Long, lpBuff As Long, nr As NETRESOURCE
            Dim cbBuff As Long, cCount As Long
            Dim p As Long, res As Long, i As Long
   
            'Setup the NETRESOURCE input structure.
            nr.dwUsage = RESOURCEUSAGE_CONTAINER
            nr.lpRemoteName = 0
            cbBuff = 1000
            cCount = &HFFFFFFFF
   
            'Open a Net enumeration operation handle: hEnum.
            res = WNetOpenEnum(RESOURCE_CONNECTED, RESOURCETYPE_ANY, _
                               0, nr, hEnum)
            If res = 0 Then
               'Create a buffer large enough for the results.
               '1000 bytes should be sufficient.
               lpBuff = GlobalAlloc(GPTR, cbBuff)
               'Call the enumeration function.
               res = WNetEnumResource(hEnum, cCount, lpBuff, cbBuff)
               If res = 0 Then
                  p = lpBuff
                  Cls
                  'WNetEnumResource fills the buffer with an array of
                  'NETRESOURCE structures. Walk through the list and print
                  'each local and remote name.
                  For i = 1 To cCount
                     CopyMemory nr, ByVal p, LenB(nr)
                     p = p + LenB(nr)
                     Print PointerToString(nr.lpLocalName), _
                           PointerToString(nr.lpRemoteName)
                  Next i
               Else
                  MsgBox "Error: " & Err.LastDllError, vbOKOnly, _
                         "WNetEnumResources"
               End If
               If lpBuff <> 0 Then GlobalFree (lpBuff)
               WNetCloseEnum (hEnum) 'Close the enumeration
            Else
               MsgBox "Error: " & Err.LastDllError, vbOKOnly, "WNetOpenEnum"
            End If
         End Sub
   
         Private Function PointerToString(p As Long) As String
            'The values returned in the NETRESOURCE structures are pointers to
            'ANSI strings so they need to be converted to Visual Basic
      Strings.
            Dim s As String
            s = String(255, Chr$(0))
            CopyPointer2String s, p
            PointerToString = Left(s, InStr(s, Chr$(0)) - 1)
         End Function
    




2. Add a new module to the project and add the following code:

   
         Option Explicit
   
         Public Type NETRESOURCE
                 dwScope As Long
                 dwType As Long
                 dwDisplayType As Long
                 dwUsage As Long
                 lpLocalName As Long
                 lpRemoteName As Long
                 lpComment As Long
                 lpProvider As Long
         End Type
   
         Public Declare Function WNetOpenEnum Lib "mpr.dll" Alias _
             "WNetOpenEnumA" ( _
             ByVal dwScope As Long, _
             ByVal dwType As Long, _
             ByVal dwUsage As Long, _
             lpNetResource As Any, _
             lphEnum As Long) As Long
   
         Public Declare Function WNetEnumResource Lib "mpr.dll" Alias _
             "WNetEnumResourceA" ( _
             ByVal hEnum As Long, _
             lpcCount As Long, _
             ByVal lpBuffer As Long, _
             lpBufferSize As Long) As Long
   
         Public Declare Function WNetCloseEnum Lib "mpr.dll" ( _
             ByVal hEnum As Long) As Long
   
         'RESOURCE ENUMERATION.
         Public Const RESOURCE_CONNECTED = &H1
         Public Const RESOURCE_GLOBALNET = &H2
         Public Const RESOURCE_REMEMBERED = &H3
   
         Public Const RESOURCETYPE_ANY = &H0
         Public Const RESOURCETYPE_DISK = &H1
         Public Const RESOURCETYPE_PRINT = &H2
         Public Const RESOURCETYPE_UNKNOWN = &HFFFF
   
         Public Const RESOURCEUSAGE_CONNECTABLE = &H1
         Public Const RESOURCEUSAGE_CONTAINER = &H2
         Public Const RESOURCEUSAGE_RESERVED = &H80000000
    




3. Execute the program. When you click on the form, a list of all the local network connections should be displayed, along with the shares they are connected to.

Keywords : kbnokeyword kbNTOS351 kbNTOS400 kbVBp400 kbVBp500 kbVBp600 kbWinOS95 kbWNet kbGrpVB
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Issue type : kbhowto