checking if program's opened

In VB, how do I write the codings so that the program checks if it has been opened already? and stop further execution at that?
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How to Prevent Multiple Instances of a VB Application;en-us;q142937
Try this code, it will also activate the previously stared instance of your program before terminating.

Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, _
                                                                    ByVal lpWindowName As String) As Long
Private Declare Function ShowWindow Lib "user32" (ByVal hwnd As Long, _
                                                ByVal nCmdShow As Long) As Long

Private Declare Function SetForegroundWindow Lib "user32" (ByVal hwnd As Long) As Long

' Put this in Form_Load

Dim Title As String

' Check if an instance of this app is already running...
If App.PrevInstance Then
    '... if so, terminate this instance and activate the previous one
    Title = frmMain.Caption
    frmMain.Caption = "NOTITLE"       ' Change title of this window to avoid finding ourself witth 'FindWindow'
    hwnd = FindWindow(vbNullString, Title)      ' Find previous instance (by looking for a window with the same caption as this one)
    If hwnd <> 0 Then
        Call SetForegroundWindow(hwnd)         ' Bring previous instance to front
        Call ShowWindow(hwnd, SW_RESTORE)
        Call CloseHandle(hwnd)
    End If
    Unload Me        ' Kill this instance
    Exit Sub
End If

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To detect if a previous instance of the application is running:

If (App.PrevInstance) Then
    MsgBox "Another instance of this application is already running.", vbExclamation + vbOKOnly, "Error"
End If
p.s., you could end it then:

To detect if a previous instance of the application is running (and End it):

If (App.PrevInstance) Then
    MsgBox "Another instance of this application is already running.", vbExclamation + vbOKOnly, "Error"
End If
java_kevinAuthor Commented:
Jonyv  , how do i declare hwnd as?
hwnd is the window handle of the form.... dim newHWnd as long

newHWnd = form1.hwnd

if you read my second comment it should explain how to prevent the same instance of the program running.  Are you trying to prevent the anohter instance of your VB program or some other program?
java_kevinAuthor Commented:
supnr, sorry about it...

You've answered quite a number of my questions. As this is an easy one, I shall give it to jonyv.

I noted that FindWindow is a declared function. It  takes in a param of Long. But I ain't sure if hwnd should be of the same type. I do not why hwnd, being a window type could be Long.

Anyway, I do agree that supnr's second comment is much simplier.. I will have to test everything in win98SE, winXP/2k. if it works (provided I can install properly as supnr should understand), points will be awarded haha.. *do I sound odd??*
"I shall give it to jonyv", that is fine with me.  As long as I could help you out.   (Another option is you could split the points between us.  But I think it is not necessory.  I got plenty of points.  Give it to jonyv)
A windowhandle (hWnd) is nothing more than a 32-bit number (= a Long), so there is no problem at all using Long as type for window handles.

Give your points to whoever provided the best solution (in your opinion) - I'm doing this mostly for fun (yeah, I'm crazy...)
"I'm doing this mostly for fun"

same here.  I like challenges and trying to find solutions for those.  this give me a chance to learn more new things every day.  Most of these questions, when I read for the first time, I don't have a clue.  But by reading and experimenting I learn a lot.  as Jonyv suggested give the points to the best solution.
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Visual Basic Classic

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