How to enumerate available COM ports on a computer?

Other than looping from 1 to 32 and trying open each 开发者_运维知识库of them, is there a reliable way to get COM ports on the system?

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I believe under modern windows environments you can find them in the registry under the following key HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM. I'm not sure of the correct way to specify registry keys. However I have only ever tested this on Windows XP.

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Check out this article from Randy Birch's site: CreateFile: Determine Available COM Ports

There's also the approach of using an MSCOMM control: ConfigurePort: Determine Available COM Ports with the MSCOMM Control

The code's a bit too long for me to post here but the links have everything you need.

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It's 1 to 255. Fastest you can do it is using QueryDosDevice like this

Option Explicit

'--- for CreateFile
Private Const GENERIC_READ                  As Long = &H80000000
Private Const GENERIC_WRITE                 As Long = &H40000000
Private Const OPEN_EXISTING                 As Long = 3
Private Const INVALID_HANDLE_VALUE          As Long = -1
'--- error codes
Private Const ERROR_ACCESS_DENIED           As Long = 5&
Private Const ERROR_GEN_FAILURE             As Long = 31&
Private Const ERROR_SHARING_VIOLATION       As Long = 32&
Private Const ERROR_SEM_TIMEOUT             As Long = 121&

Private Declare Function QueryDosDevice Lib "kernel32" Alias "QueryDosDeviceA" (ByVal lpDeviceName As Long, ByVal lpTargetPath As String, ByVal ucchMax As Long) As Long
Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, ByVal lpSecurityAttributes As Long, ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long

Private Function PrintError(sFunc As String)
    Debug.Print sFunc; ": "; Error
End Function

Public Function IsNT() As Boolean
    IsNT = True
End Function

Public Function EnumSerialPorts() As Variant
    Const FUNC_NAME     As String = "EnumSerialPorts"
    Dim sBuffer         As String
    Dim lIdx            As Long
    Dim hFile           As Long
    Dim vRet            As Variant
    Dim lCount          As Long

    On Error GoTo EH
    ReDim vRet(0 To 255) As Variant
    If IsNT Then
        sBuffer = String$(100000, 1)
        Call QueryDosDevice(0, sBuffer, Len(sBuffer))
        sBuffer = Chr$(0) & sBuffer
        For lIdx = 1 To 255
            If InStr(1, sBuffer, Chr$(0) & "COM" & lIdx & Chr$(0), vbTextCompare) > 0 Then
                vRet(lCount) = "COM" & lIdx
                lCount = lCount + 1
            End If
        Next
    Else
        For lIdx = 1 To 255
            hFile = CreateFile("COM" & lIdx, GENERIC_READ Or GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0, 0)
            If hFile = INVALID_HANDLE_VALUE Then
                Select Case Err.LastDllError
                Case ERROR_ACCESS_DENIED, ERROR_GEN_FAILURE, ERROR_SHARING_VIOLATION, ERROR_SEM_TIMEOUT
                    hFile = 0
                End Select
            Else
                Call CloseHandle(hFile)
                hFile = 0
            End If
            If hFile = 0 Then
                vRet(lCount) = "COM" & lIdx
                lCount = lCount + 1
            End If
        Next
    End If
    If lCount = 0 Then
        EnumSerialPorts = Split(vbNullString)
    Else
        ReDim Preserve vRet(0 To lCount - 1) As Variant
        EnumSerialPorts = vRet
    End If
    Exit Function
EH:
    PrintError FUNC_NAME
    Resume Next
End Function

The snippet falls back to CreateFile on 9x. IsNT function is stubbed for brevity.

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Using VB6 or VBScript to enumerate available COM ports can be as simple as using VB.NET, and this can be done by enumerating values from registry path HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM. It's better than calling QueryDosDevice() and doing string comparison to filter out devices which's name is leading by COM since you will get something like CompositeBattery (or other stuff which have full upper case name leading by COM) that isn't a COM port. Another benefit of doing this is that the registry values also containing USB to COM devices, which could not be detected by using the codes such as WMIService.ExecQuery("Select * from Win32_SerialPort"). If you try to plug the USB to COM devices in or out of the computer, you can see the registry values also appear or disappear immediately, since it's keeping updated.

Option Explicit

Sub ListComPorts()
List1.Clear

Dim Registry As Object, Names As Variant, Types As Variant
Set Registry = GetObject("winmgmts:\\.\root\default:StdRegProv")
If Registry.EnumValues(&H80000002, "HARDWARE\DEVICEMAP\SERIALCOMM", Names, Types) <> 0 Then Exit Sub

Dim I As Long
If IsArray(Names) Then
    For I = 0 To UBound(Names)
        Dim PortName As Variant
        Registry.GetStringValue &H80000002, "HARDWARE\DEVICEMAP\SERIALCOMM", Names(I), PortName
        List1.AddItem PortName & " - " & Names(I)
    Next
End If

End Sub

Private Sub Form_Load()
ListComPorts
End Sub

The code above is using StdRegProv class to enumerate the values of a registry key. I've tested the code in XP, Windows 7, Windows 10, and it works without any complainant. The items which were added to the Listbox looks like below:

COM1 - \Device\Serial0
COM3 - \Device\ProlificSerial0

The downside of this code is that it could not detect which port is already opened by other programs since every port could only be opened once. The way to detect a COM port is opened by another program or not can be done by calling the API CreateFile. Here is an example.