Broadcasting in UDP

[scorrpeio]

I want to know the IP & port of the machines. For this purpose I am broadcasting any message through UDP socket.

But I dont receive any message(even from my machine).
Is it possible to code such a way that when dialog box is created, the constructor itself broadcast the message & listen to the reply. If reply occurs it will find out the IP & port of that machine.

If it is possible in VC++. PLease let me know how. I have done this(sorry, for it is wrong) but not up to the mark..............

int BroadCastInitial;
		int iBroadCast = 0;
		int rflag = 0, flag =1, len = 0;

		BroadCastInitial = UDPSockptr -> SetSockOpt( SO_BROADCAST, &flag, sizeof( int ) );

		if ( !BroadCastInitial )
		{
			wsprintf(m_SocError, "SetSockOpt failed to set SO_BROADCAST:% d", UDPSockptr->GetLastError());
			delete UDPSockptr;
			UDPSockptr = NULL;
			AfxMessageBox ( m_SocError );
			
		}
		
		sockaddr_in m_RemoteAdd;
		m_RemoteAdd.sin_family = AF_INET;
		m_RemoteAdd.sin_addr.s_addr = inet_addr( "255.255.255.255" );
		m_RemoteAdd.sin_port = htonl( INADDR_BROADCAST );
		
		iBroadCast = UDPSockptr -> SendTo("AnyBody here me?",20, (const SOCKADDR*) &m_RemoteAdd, sizeof ( m_RemoteAdd ) );
		if ( !iBroadCast )
		{
			
			wsprintf(m_SocError, " Broadcasting failed % d", UDPSockptr->GetLastError());
			AfxMessageBox ( m_SocError );
			
		}
		else
		{
			AfxMessageBox ( "Broadcasting successful" );
		}
		
        len = sizeof(rflag);

		if ( UDPSockptr -> GetSockOpt( SO_BROADCAST, &rflag, &len ) && rflag == 0 )
		{
			wsprintf( m_SocError, "GetSockOpt failed to get SO_BROADCAST:% d", UDPSockptr -> GetLastError());
			delete UDPSockptr;
			UDPSockptr = NULL;
			AfxMessageBox ( m_SocError );			
		}
		else
		{
			AfxMessageBox( "Msg received" );  
		}

I called this function in the constructor. It gets executed without error. But, sent message is not displayed

[VictorN]

Note that the most of network administrators do NOT allow any UDP (neither sockets nor mailslots).
However, your own computer is supposed to receive those messages.

[Edders]

@VictorN - are you sure about your statement that "most of network administrators do NOT allow any UDP" as I've never come across that situation. Or did you mean broadcast messages?

[VictorN]

... Or did you mean broadcast messages?

You are right! I meant broadcast messages. Sorry!

[scorrpeio]

In my network broadcast messages are allowed as I have checked out the same using another EXE.

The issue is how to achieve this, I mean get the IP of the machine using the application

[VictorN]

Have a look at this thread and at the pointed out FAQ.

[Maximus_X]

Scorrpeio, I should expect a while() { ... } block that contains the messages received code, not only a single GetSockOpt() call.

[scorrpeio]

@Maximus X, I dont get your point clearly

@Victor, Thank you for the link. But, corresponding discussion was about getting the IP/name of the machine which uses the application(sorry, I did mistake in last reply by saying that I want such function which could give me the name of only single PC )
I want to know the IP/names of all the machines which are using the application. just like in LAN messenger we can see the available names.

Please suggest me the solution

[Maximus_X]

@Maximus X, I dont get your point clearly

At this moment your code fails because I cannot received instantaneous good result. So you need to wait the right answer in a while block.
I suppose and guess that you are using a second thread code for this broadcast code. Well from the application interface, you can control this while using a bool flag:

while(!pObject->m_bStatus)
{
  		if ( UDPSockptr -> GetSockOpt( SO_BROADCAST, &rflag, &len ) && rflag == 0 )
		{
			wsprintf( m_SocError, "GetSockOpt failed to get SO_BROADCAST:% d", UDPSockptr -> GetLastError());
			delete UDPSockptr;
			UDPSockptr = NULL;
			AfxMessageBox ( m_SocError );			
		}
		else
		{
			AfxMessageBox( "Msg received" );  
		}     
}

But be careful... don't use AfxMessageBox() inside of while block because it stops your thread over it.

[scorrpeio]

Have a look at this thread and at the pointed out FAQ.

Thank you for the link. But, corresponding discussion was about getting the IP/name of the machine which uses the application(sorry, I did mistake in last reply by saying that I want such function which could give me the name of only single PC )
I want to know the IP/names of all the machines which are using the application. just like in LAN messenger we can see the available names.

Please suggest me the solution

[Mihai Greavu]

salve scorrpeio,

Something looks a bit dubious.
Are you positive on this line: m_RemoteAdd.sin_port = htonl( INADDR_BROADCAST ); ?
INADDR_BROADCAST is usually a placeholder for the bcast addr 255.255.255.255.

You should pass a port number. INADDR_BROADCAST is equivalent to 0xffffffff.
sin_port being an unsigned short gives you portnumber 65535. Is this your intended usage ?

Also check the send/receive buffer sizes.