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Hi.........
I wrote the following code to listen to UDP data sent at specified port by any machine using any application....
I used dialog box application....
m_DataReceived is variable of Edit Control box
m_PortNo is varible to get the port no.
When the connectme button is clicked the following code executes....
Code:
UpdateData( TRUE );
if( !m_PortNo )
MessageBox( "Please enter the Port No & then click \"Connect Me\"" );
return;
WSADATA wsaData;
SOCKET RecvSocket;
sockaddr_in RecvAddr;
int Port = 6791;
char RecvBuf[1024];
int BufLen = 1024;
sockaddr_in SenderAddr;
int SenderAddrSize = sizeof(SenderAddr);
char m_SocError[23];
// Initialize Winsock
WSAStartup(MAKEWORD(2,2), &wsaData);
// Create a receiver socket to receive datagrams
RecvSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
// Bind the socket to any address and the specified port.
RecvAddr.sin_family = AF_INET;
RecvAddr.sin_port = htons(m_PortNo);
RecvAddr.sin_addr.s_addr = inet_addr( "255.255.255.255" );
int BindCheck = bind(RecvSocket, (SOCKADDR *) &RecvAddr, sizeof(RecvAddr));
if( 0 != BindCheck )
AfxMessageBox("SocketBind");
if(recvfrom(RecvSocket,RecvBuf,BufLen,0,(SOCKADDR *)&SenderAddr,&SenderAddrSize)== SOCKET_ERROR)
MessageBox("ERROR");
m_DataReceived = RecvBuf;
UpdateData(FALSE);
closesocket(RecvSocket);
WSACleanup();
exit(1) ;
However though binding is successful I get the Error 10022 : WSAEINVAL
That means the parameter in the recvfrom() are invalid
Please suggest me How to remove this error? what changes to make in the recvfrom function
Please help me!
I came to realise that socket binding is failed!!!
By mistake I used Bindchek == 0; instead of BindChek != 0 in the if loop....
Now the question is why binding is failed???
char RecvBuf[500];
int BufLen = 501;
int SenderAddrSize = sizeof(SenderAddr);
CString MultiLine = _T("\r\n");
// Initialize Winsock
int iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
if (iResult != NO_ERROR)
MessageBox( "WSAStartup failed" );
return;
// Create a receiver socket to receive datagrams
RecvSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
// Bind the socket to any address and the specified port.
RecvAddr.sin_family = AF_INET;
RecvAddr.sin_port = htons( Port );
RecvAddr.sin_addr.s_addr = htonl( INADDR_ANY );
int BindCheck = bind( RecvSocket, ( SOCKADDR * ) &RecvAddr, sizeof( RecvAddr ) );
if( 0 != BindCheck )
wsprintf( m_SocError, "GetSockOpt failed to get SO_BROADCAST:%d", GetLastError());
MessageBox( "SocketBind Failed" );
return;
int RecvChek = recvfrom( RecvSocket, RecvBuf, BufLen, 0, (SOCKADDR *)&SenderAddr, &SenderAddrSize );
if( RecvChek == SOCKET_ERROR )
m_DataReceived = MultiLine + "ERROR in Receiving" ;
UpdateData( FALSE );
m_DataReceived = "";
RecvBuf[RecvChek] = '\0';
m_DataReceived = RecvBuf;
UpdateData( FALSE );
//goto AGAIN;
/*closesocket(RecvSocket);
WSACleanup();
exit(1) ;*/
This code just works for one event...I mean accept packet once only.....
How to make it run for long.....
If I use while loop....it does not show any problem but the dialog box doesnot get closed even if I cilck on close button on extreme upper right corner.
I have to close it through task manager.
Please tell me how to overcome this problem
Very strange... 
Anyway, since I don't use UDP (our and many many other sysadmins don't allow broadcasting, and without broadcasting I don't see any advantage of using UDP) I cannot help you more.
However, you might consider change the socket type to SOCK_STREAM: 
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