Imports System.Runtime.InteropServices

    'strutture per recuperare le informazioni sulla porta (per ora mi basta PORT_INFO_1)
    Public Structure PORT_INFO_1
        Dim pPortName As String
    End Structure
    Public Structure PORT_INFO_2
        Dim pPortName As String
        Dim pMonitorName As String
        Dim pDescription As String
        Dim fPortType As Integer
        Dim Reserved As Integer
    End Structure
    'aggiunge una porta
    Public Declare Function AddPortEx Lib "winspool.drv" Alias "AddPortExA" (ByVal pName As String, ByVal pLevel As Integer, ByRef lpBuffer As _
PORT_INFO_1, ByVal pMonitorName As String) As Integer

    'recupera l'elenco di porte installate
    'EnumPorts member descriptions:
    'pName: String specifying the name of the server whose
    'printer ports you wish to enumerate. If pName is
    'vbNullString, the function enumerates the local
    'machine's printer ports.

    'nLevel: Specifies the type of information returned in
    'the lpbPorts buffer. If nLevel is 1, lpbPorts receives
    'an array of PORT_INFO_1 structures. If nLevel is 2,
    'lpbPorts receives an array of PORT_INFO_2 structures.

    'lpbPorts: Pointer to a buffer that receives an array of
    'PORT_INFO_1 or PORT_INFO_2 structures. Each structure
    'contains data that describes an available printer port.
    'The buffer must be large enough to store the strings
    'pointed to by the structure members.

    'cbBuf: the size, in bytes, of the buffer pointed to by lpbPorts.

    'pcbNeeded: receives the number of bytes copied to the lpbPorts
    'buffer. If the the buffer is too small, the function fails and
    'the variable receives the number of bytes required.

    'pcReturned: variable that receives the number of PORT_INFO_1 or
    'PORT_INFO_2 structures returned in the pPorts buffer. This
    'corresponds to the number of printer ports that are available
    'on the specified machine.
    Declare Function EnumPorts Lib "winspool.drv" Alias "EnumPortsA" _
        (ByVal pName As String, ByVal Level As Integer, ByVal lpbPorts As IntPtr, _
        ByVal cbBuf As Integer, ByRef pcbNeeded As Integer, ByRef pcReturned As Integer) As Integer

    'controlla se la porta esiste, altrimenti la crea
    Private Sub AddPort(ByVal PortName As String)
        Dim ret, pcbNeeded, pcReturned As Integer
        Dim TempBuff As IntPtr, i As Short
        Dim FoundedPorts() As PORT_INFO_1 'elenco delle porte trovate
        Dim Found As Boolean = False 'indica se la porta è già installata
        Try
            'NOTA: modifica del codice proposto su http://vbcity.com/forums/topic.asp?tid=47438 utilizzando PORT_INFO_1 anziché PORT_INFO_2

            ' Make the first call to the function
            ret = EnumPorts("", 1, TempBuff, 0, pcbNeeded, pcReturned)
            ' Set the size of the pointer to return the data based upon the size of the buffer required
            TempBuff = Marshal.AllocHGlobal(pcbNeeded + 1)
            ' Make the call again with the buffer set
            ret = EnumPorts("", 1, TempBuff, pcbNeeded, pcbNeeded, pcReturned)
            ' Determine whether the call was successful
            If ret Then
                ' Set the pointer to process as the first one returned
                Dim CurrentPort As IntPtr = TempBuff
                ' Re-dimension the array of port structures
                ReDim FoundedPorts(pcReturned)
                ' Loop through the results
                For i = 1 To pcReturned
                    ' Convert the pointer to a structure
                    FoundedPorts(i) = Marshal.PtrToStructure(CurrentPort, GetType(PORT_INFO_1))
                    If FoundedPorts(i).pPortName = PortName Then
                        Found = True
                    End If
                    ' Obtain the next port pointer from the buffer
                    CurrentPort = IntPtr.op_Explicit(CurrentPort.ToInt32 + Marshal.SizeOf(GetType(PORT_INFO_1)))
                Next
            End If
            FoundedPorts = Nothing
            If Not Found Then 'se la porta non esiste già, viene aggiunta
                Dim Port As New PORT_INFO_1
                Port.pPortName = PortName
                AddPortEx(Nothing, 1, Port, "Local Port")
            End If
        Catch ex As Exception
            'gli errori andranno gestiti dal chiamante
            Throw ex
        End Try
    End Sub