Com port availability

Question

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i want to select a comport from a list of ports using combobox using vb6.i'm unable to write a code on that so pls help me.

What I have tried:

VB

Private Sub form_load()

    Dim i As Long
    For i = 1 To 16
        If COMAvailable(i) Then
            Combo1.AddItem "COM" & i & ""
        Else
            Combo1.AddItem "COM" & i & ""
        End If
    Next
    
End Sub

Private Sub Command1_Click()
    
    If COMAvailable(i) = True Then
        
        Label1.Caption = "READY FOR COMMUNICATION"
    Else
        Label1.Caption = "PORT NOT OPEN PLEASE CONFIGURE"
    End If
    
End Sub

Posted 7-Dec-17 23:27pm

Member 13396059

Updated 8-Dec-17 0:27am

CPallini

v2

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Comments

Richard MacCutchan 8-Dec-17 5:45am

Where is the code for the COMAvailable method?

Member 13396059 8-Dec-17 5:50am

Public Function COMAvailable(ByVal iPortNum As Integer) As Boolean

Dim hCOM As Long
Dim ret As Long
Dim sec As SECURITY_ATTRIBUTES

'try to open the COM port

hCOM = CreateFile("COM" & iPortNum & "", 0, FILE_SHARE_READ + FILE_SHARE_WRITE, _
sec, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0)
If hCOM = -1 Then
COMAvailable = False
Else
COMAvailable = True
'close the COM port
ret = CloseHandle(hCOM)
End If

End Function

Richard MacCutchan 8-Dec-17 5:57am

OK, so are you going to tell us what the problem is?

Member 13396059 8-Dec-17 6:03am

i am askin for help

Richard MacCutchan 8-Dec-17 6:07am

Then tell us what the problem is. We cannot read your mind.

Member 13396059 8-Dec-17 6:08am

i want to select a comport from a combo box and open the com port which is available

Richard MacCutchan 8-Dec-17 6:10am

And? What is preventing you from doing that?

Member 13396059 8-Dec-17 6:12am

every time when i'm running the program when i'm selecting the com port which is available also its showing that port not open pls configure

CPallini 8-Dec-17 6:08am

Why are you unhappy with such code?

Member 13396059 8-Dec-17 6:10am

i want to select a comport and open it to send and receive data from a combo box

Richard MacCutchan 8-Dec-17 6:12am

Please stop posting non-explanations, and telling us what you want. Explain in proper detail exactly what is not working.

Richard MacCutchan 8-Dec-17 6:11am

The usual reason I suspect.

Member 13396059 8-Dec-17 6:14am

i'm unable to open the port

[no name] 8-Dec-17 6:31am

a.) You add the COM Port to the Combo box also if it is not detected by COMAvailable
b.) What I think to remember is for COM Ports >= 10 you need to use this Filename: "\\.\COM10"

Member 13396059 8-Dec-17 6:59am

i have already added com port to combo box.but its not working

[no name] 8-Dec-17 7:08am

That is you Problem I think, you add it in any case, even it is not available. Your code:


If COMAvailable(i) Then
            Combo1.AddItem "COM" & i & ""
        Else
            Combo1.AddItem "COM" & i & ""
        End If

Richard Deeming 8-Dec-17 11:55am

Where does the variable i come from in your Command1_Click method? The only place it seems to be declared is as a local variable with the form_load method, and that's not going to be available outside of that method.

Are you compiling your code without setting Option Explicit on?

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Jochen Arndt · Answer 1 · 2017-12-08T00:27:00

If you really need to do it with VB6, search the web for solutions using something like "vb6 enumerate serial ports" as search term.

Don't try to do it yourself. There are a lot of things to observe like naming of ports with numbers above 9 and that CreateFile fails not only for not existing ports but also for existing ports that are actually opened (in use).

The only reliable method besides the .NET SerialPort.GetPortNames method is using the Windows Setup API. But I don't know if someone has used that with VB6.

[EDIT: Notes on code posted as comment]

Quote:
every time when i'm running the program when i'm selecting the com port which is available also its showing that port not open pls configure

That is because this always fails due to the wrong share mode:

VB

hCOM = CreateFile("COM" & iPortNum & "", 0, FILE_SHARE_READ + FILE_SHARE_WRITE, _
sec, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0)

CreateFile function (Windows)[^]:
For communications resources, the dwCreationDisposition parameter must be OPEN_EXISTING, the dwShareMode parameter must be zero (exclusive access), and the hTemplateFile parameter must be NULL. Read, write, or read/write access can be specified, and the handle can be opened for overlapped I/O.

To specify a COM port number greater than 9, use the following syntax: "\\.\COM10". This syntax works for all port numbers and hardware that allows COM port numbers to be specified.

So it should be:

VB

hCOM = CreateFile("\\.\COM" & iPortNum, GENERIC_READ + GENERIC_WRITE, 0, _
ByVal 0&, OPEN_EXISTING, 0, 0&)

[/EDIT]