Binaryworld - Check whether a serial or parallel port is available ... [ VB -> Windows ]

The Open statement also supports special device names such as COM1 or LPT2. You can build on this feature and use the Open command to test whether a given serial or parallel port is available. Here are two functions that perform this task:

Click here to copy the following block

' Check whether a given COM serial port is available

Function IsComPortAvailable(ByVal portNum As Integer) As Boolean
  Dim fnum As Integer
  On Error Resume Next
  fnum = FreeFile
  Open "COM" & CStr(portNum) For Binary Shared As #fnum
  If Err = 0 Then
    Close #fnum
    IsComPortAvailable = True
  End If
End Function

' Check whether a given LPT parallel port is available

Function IsLptPortAvailable(ByVal portNum As Integer) As Boolean
  Dim fnum As Integer
  On Error Resume Next
  fnum = FreeFile
  Open "LPT" & CStr(portNum) For Binary Shared As #fnum
  If Err = 0 Then
    Close #fnum
    IsLptPortAvailable = True
  End If
End Function

You can use the above function also for determining how many serial or parallel ports are installed, using a loop:

Click here to copy the following block

Dim count As Integer, i As Integer
For i = 1 To 16
If IsComPortAvailable(i) Then count = count + 1
Next
MsgBox "Found " & count & " serial ports"