C / C++ / MFC

7-Apr-04 5:45

Hi,

How can I add something to a listbox, AFTER it's initialized?
First, I use this code:

BOOL CDialog1::OnInitDialog()
{
CDialog::OnInitDialog();
m_ListBox.AddString("jef");
return true ;
}

and this works fine. But I want to be able to add other items afterwards (to be precise, I would like to be able to show the user which webcams are available.)

So I made a function:

void CCamDialog::AddListBox()
{
m_ListBox->AddString("camera");
}

But this gives an error (debg assertion failed).

any ideas?

thanks

David Crow7-Apr-04 5:47

David Crow

7-Apr-04 5:47

When is AddListBox() getting called? If it is before the listbox window actually exists, you obviously cannot add to it.

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Wes Aday7-Apr-04 11:13

Wes Aday

7-Apr-04 11:13

You are trying to do 2 different things.

BOOL CDialog1::OnInitDialog()
m_ListBox.AddString("jef");

This list box belongs to CDialog1.

void CCamDialog::AddListBox()
{
m_ListBox->AddString("camera");
}

This listbox belongs to CCamDialog.

As I understand what you are trying to do, you are trying to add "camera" to the same listbox as "jef". Unless you have a pointer to the CDialog1::m_Listbox in the CCamDialog, you are trying to add "camera" to a listbox that may or may not exist. My guess is that CCamDialog::m_Listbox doesn't exists and that will give you a assertion failure.

Artificial intelligence is no match for natural
stupidity.

Qualvis7-Apr-04 11:46

7-Apr-04 11:46

Sorry for that, Guess I copied it wrong (I was trying to make it work in an other application)
It should be

BOOL CDialog1::OnInitDialog()
{
CDialog::OnInitDialog();
m_ListBox.AddString("jef");
return true ;
}

and

void CDialog1::AddListBox()
{
m_ListBox.AddString("camera");
}

Wes Aday7-Apr-04 12:09

Wes Aday

7-Apr-04 12:09

Okay. Now I have 2 questions. Where is the AddListBox function being called from? and what is the assertion failure that you are getting?

Artificial intelligence is no match for natural
stupidity.

Qualvis7-Apr-04 22:08

7-Apr-04 22:08

Addlistbox is being called like this:

void CDialogTestApp::OnTest1()
{
CDialog1 d1;
d1.AddListBox();
d1.DoModal();
}

(with ontest1 being an eventhandler when i press a menuitem)

The Failure isn't much of a help (well, not for me...) , It only says Debug Assertion Failure, and when I press "retry", it gives another error, "unhandled exception at 0x7c25bec6(mfc70d.dll) in DialogTest.exe: User Breakpoint"

thanks for your help btw! It's very much appreciated...

Qualvis7-Apr-04 22:32

7-Apr-04 22:32

I found a way (well somebody told me a way Wink | ;-)

) to do it.

I just added a stringarray to my Dialog, which I could fill before the Initialization, and then I could just add the items in the string to my listbox.

Thanks for helping me!

Re: setting page orientation

Wes Aday8-Apr-04 7:08

Wes Aday

8-Apr-04 7:08

Qualvis wrote:
void CDialogTestApp::OnTest1()
{
CDialog1 d1;
d1.AddListBox();
d1.DoModal();
}

I believe that would be your problem. You are instantiating the dialog but then trying to add things to a control that doesn't exist yet.

Artificial intelligence is no match for natural
stupidity.

setting page orientation

kzyczynski7-Apr-04 5:31

kzyczynski

7-Apr-04 5:31

Hello

I have in my app. print button. My app. must print in "landscape" mode
only, because there are some long tables to print.

Could someone tell me how to set up this option (page orientation) programatically? Or some tips. Anything will do Smile | :)

thank you
Chris

Roger Allen7-Apr-04 5:38

Roger Allen

7-Apr-04 5:38

If its an MFC app, it will have an DEVMODE object which is a member of your CWinApp class. Call these functions and pass throught the required page orientation

bool SetPrintOrientation(HANDLE &hDevMode, int mode) const
{
	if (hDevMode == INVALID_HANDLE_VALUE)
		return false ;

	switch (mode)
		{
		case DMORIENT_PORTRAIT :
				{
				// portrait mode
				LPDEVMODE pDevMode = (LPDEVMODE)::GlobalLock(hDevMode) ;
				// set orientation to portrait
				pDevMode->dmOrientation = DMORIENT_PORTRAIT ;
				::GlobalUnlock(hDevMode) ;
				}
				break ;
		case DMORIENT_LANDSCAPE :
				{
				// landscape mode
				LPDEVMODE pDevMode = (LPDEVMODE)::GlobalLock(hDevMode) ;
				// set orientation to landscape
				pDevMode->dmOrientation = DMORIENT_LANDSCAPE ;
				::GlobalUnlock(hDevMode) ;
				}
				break ;
		default :	
				ASSERT(FALSE) ;		// invalid parameter
				return false ;
		}
	return true ;
}

int GetPrintOrientation(HANDLE &hDevMode)
{
	int	val = DMORIENT_PORTRAIT ;
	if (hDevMode != INVALID_HANDLE_VALUE && hDevMode != NULL)
		{
		// get the current value from the structure
		LPDEVMODE pDevMode = (LPDEVMODE)::GlobalLock(hDevMode) ;
		val = pDevMode->dmOrientation ;
		::GlobalUnlock(hDevMode) ;
		}
	return val ;
}

Roger Allen - Sonork 100.10016
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Re: setting page orientation

kzyczynski7-Apr-04 10:20

kzyczynski

7-Apr-04 10:20

thanks. it looks good. And Yes it Is MFC application but there is a problem.
i tried it on:
protected:
HGLOBAL m_hDevMode;
member of CWinApp
and in pInfo->m_pPD->m_pd.hDevMode in CPrintInfo.
And the problem is that this variables are always 0 and i have an exception
in SetPrintOrientation(..) function

Can you give me some more tips?

thanks in advance

-- added later ---
ok i found solution
i must call GetPrinterDeviceDefaults(..) first

Socket listen backlog woes

Rob Caldecott7-Apr-04 5:15

Rob Caldecott

7-Apr-04 5:15

OK, I think I might know what the answer to this is going to be, put I'll post my problem anyway, as you never know, there may be a simpler solution...

I have a service app that listems for incoming socket connections using good old Berkeley style socket code - I have code that creates the socket to listen on and then a thread that uses "select" to wait for the connections, spawning a new thread per-connection to handle the data, e.g.:

<br />
for ( ; ; )<br />
{<br />
    ...<br />
    fd_set read;<br />
    FD_ZERO(&read);<br />
    FD_SET(m_hSocket, &read);<br />
    int nResult = ::select(-1, &read, NULL, NULL, &tv);<br />
    if (nResult == 1)<br />
    {<br />
        // Accept the connection<br />
        SOCKET s = ::accept(read.fd_array[i], NULL, NULL);<br />
       // Create a thread to process the incoming connection<br />
      AfxBeginThread(...);<br />
    }<br />
}<br />

The problem is that if I hammer the app using a test program that creates lots of simultaneous connections to the server (using a separate thread for each all started at once), before long some of these connections will fail with WSAECONNREFUSED. This seems to be because creating the thread to handle the accepted socket in the code above is expensive in terms of CPU and the incoming connections piling up whilst I am doing this are causing the backlog (5 sockets?) to be exceeded.

I *think* the answer will be to use IO completion ports but this is going to be a big job. The threads I create to process each socket are short-lived, and I know IOCP can ensure fewer are needed but will it also help with this backlog problem or is there another more generic way to handle this? At some point in the distant future I may want to port the code to Linux (yikes!) so I wanted to avoif anything MS specific.

Comments?

The Rob Blog

beetung7-Apr-04 8:14

beetung

7-Apr-04 8:14

Why spawn a thread *AFTER* a connection attempt? Prepare a pool of worker threads all waiting on a single semaphore would be the easiest fix I believe(least effort on your part)... after all, triggering a single semaphore event should cost a fraction of AfxBeginThread(...)

try Recycle all threads instead of respawn... and dont harm any animals. Unsure | :~

-Dan

Rob Caldecott7-Apr-04 9:53

Rob Caldecott

7-Apr-04 9:53

Cheers for the tip - I will investigate further...

The Rob Blog

Johnny ²7-Apr-04 8:56

Johnny ²

7-Apr-04 8:56

First, you should be able to set the backlog value to much higher than 5. This will ease most problems immediatley. You've not shown the listen section so I will assume you've used a large value.

Second, you could split the code into two threads:

Thread 1 sits waiting for new connections, accepts them, and puts the socket handle into a queue. Thats all it does - it then immediatley resumes accepting other connections.

Thread 2 sits on the queue, and creates a thread for each socket.

This detachs the (slow) thread creation process from the (fast) accept process, and you should be able to pretty much reach the maximum accept rate you can.

Rob Caldecott7-Apr-04 9:52

Rob Caldecott

7-Apr-04 9:52

Using winsock2, the maximum backlog value is apparently now 0x7fffffff (SOMAXCONN) but I tried this without any success. I will experiment with new values.

I also tried two threads as you suggested, using a shared array of SOCKETs - the accept thread adds the accepted socket to the list and then signals the second thread via a semaphore, but still I had problems. I used a critical section to protect the shared socket array, but perhaps I need to revisit this.

Thanks for the advice - switching to IOCP and AcceptEx is a major task that itself looks fraught with problems if my search of Google Groups is anything to go by! Wink | ;)

The Rob Blog