Re: theApp.ExitInstance(); returns 20 - what does this mean?

Scot Brennecke <>
Mon, 09 Nov 2009 00:12:05 -0600
David Ching wrote:

"Mechi" <> wrote in message

I have a dialog based application. It always exits with 20 - though i
think it should exit with 0.

In a dialog application, you typically show the dialog in
InitInstance(), wait for the DoModal() call to return, then return FALSE
from InitInstance() so your app closes without starting a message pump.

Because you do not override ExitInstance() (and it is not even called)
in this scenario, you don't have the ability to set a proper return
code. Essentially the return code is garbage depending on the last
message pumped, I believe.

Bottom line is if you care about the return code, you can't call
DoModal() in InitInstance() like this. Instead you need to start a
message pump so that ExitInstance is called. This typically means
showing a CMainFrame (perhaps with no menu bar, toolbar, or status bar)
containing a CFormView of your original dialog.

The only thread that is opened is the
GUI/dialog itself. I open and then immediately (afte GUI is
displayed) close the application.

int nResponse = dlg.DoModal();


I call (just to be able to catch the error):

int err = theApp.ExitInstance();

err returns = 20.

I don't know how CWinApp::ExitInstance() determines it's return value,
but it doesn't really matter because there is no way for you to then set
this value to the return value of your app.

I traced into thrdcore.cpp, below.

MSG* AFXAPI AfxGetCurrentMessage()
_AFX_THREAD_STATE* pState = AfxGetThreadState();
return &(pState->m_msgCur);

There is obviously a thread wtill running - as I saw in the Thread
3084 __tmainCRTStartup CCamelotSampleApp::InitInstance Normal 0
2244 Win32 Thread _KiFastSystemCallRet@0 Normal 0

How do I ensure that the GUI thread closes before the application

It does. But you haven't returned from CCamelotSampleApp::InitInstance()
yet when you look at the call stack; you are looking too early.

-- David

Just some minor corrections, although the bulk of your answer is on
target. CWinApp is derived from CWinThread, and when InitInstance
returns false, this leads to a call to pThread->ExitInstance. This
becomes a call to CWinApp::ExitInstance. If AfxGetCurrentMessage
returns a non-NULL current MSG pointer, then ExitInstance will return
the wParam from that message.

But Joe's reply about it being unusual to care about the return value
from GUI app is appropriate here. A simple debugging session should
yield the answers, though.

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