Question

I have a problem with a c++ socket.
I’m using CAsyncSocket from MFC that i want to join a multicast group.
Also I need to have multiple listener on this group and here is where i get in trouble.
I found some examples on the web but it doesn’t seems to work.
Here is my code:

//create socket on port 17233   
BOOL bRet = Create(17233,SOCK_DGRAM, FD_READ);

//set reuse socket option  
BOOL bMultipleApps = TRUE;
bRet = SetSockOpt(SO_REUSEADDR, (void*)&bMultipleApps, sizeof(BOOL), SOL_SOCKET);

//join multicast group
ip_mreq m_mrMReq;           // Contains IP and interface of the host group
m_mrMReq.imr_multiaddr.s_addr = inet_addr((LPCSTR)"224.30.0.1");    /* group addr */ 
m_mrMReq.imr_interface.s_addr = htons(INADDR_ANY);      /* use default */

int uRes =setsockopt(m_hSocket, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char FAR *)&m_mrMReq, sizeof(m_mrMReq));

There are no errors when i run this.
But when i try to run another instance of the app it fails to create a new socket on that port because the port is in use.

I have done this in C# and it worked fine like this:

IPEndPoint ipep = new IPEndPoint(IPAddress.Any, port);
s.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, 1);
s.Bind(ipep);
IPAddress ip = IPAddress.Parse(mcastGroup);
s.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(ip, IPAddress.Any));
s.SetSocketOption(SocketOptionLevel.IP,SocketOptionName.MulticastTimeToLive, int.Parse("1"));

So if any body sees a problem with my code or have some tips i will gladly appreciated.

EDIT 1:
Is CAsyncSocket a TCP socket?

EDIT 2:
After reading Can two applications listen to the same port?
I think i made a confusion. I need a Multicast UDP port that can be access by multiple application using SO_REUSEADDR

Edit for Clarification:

BOOL bRet = Create(17233,SOCK_DGRAM, FD_READ)

Creates an UDP socket and bind’s to to port 17223.
For SetSockOpt(SO_REUSEADDR, (void*)&bMultipleApps, sizeof(BOOL), SOL_SOCKET); to work you need to set it before binding as @Hasturkun said.
The final working code looks like this:

    BOOL bRet = Socket(SOCK_DGRAM, FD_READ);
    if(bRet != TRUE)
    {
        UINT uErr = GetLastError();
        std::cout<<"Error:"<<uErr<<std::endl;
        return FALSE;
    }else{
        std::cout<<"Create sock: OK"<<std::endl;
    }

    //add reuse
    BOOL bMultipleApps = TRUE;      /* allow reuse of local port if needed */
    SetSockOpt(SO_REUSEADDR, (void*)&bMultipleApps, sizeof(BOOL), SOL_SOCKET);

    //bind
    bRet = Bind(17233, NULL);
    if(bRet != TRUE)
    {
        UINT uErr = GetLastError();
        std::cout<<"Error(BIND):"<<uErr<<std::endl;
    }else{
        std::cout<<"BIND sock: OK"<<std::endl;
    }

Thanks,
Gabriel

;

Answer 1

You should be able to separate the creation of the socket from the binding, create the socket using Socket, eg.

BOOL bRet = Socket(SOCK_DGRAM, FD_READ);

Then bind it with Bind after setting the sockopt

BOOL bMultipleApps = TRUE;
bRet = SetSockOpt(SO_REUSEADDR, (void*)&bMultipleApps, sizeof(BOOL), SOL_SOCKET);

bRet = Bind(17233, NULL);