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Tip of the Day
Language: VB4,VB5,VB6
Expertise: beginner
Dec 4, 1999

Check whether a serial or parallel port is available

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:


' 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:


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"
Francesco Balena
 
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