Thread: Sockets Problem C++

Well, I don't know how much help this will be to you but here is how I do it (with UDP) in ANSI-C... The example is very incomplete since I'm not about to give away all my secrets However you can see how to open a port, wait till it's not busy before sending, receive datagrams asynchronously using a thread, and how to shut things down when you're done....

Code:

/////////////////////////////////////////////////////////////////////////////////////////
// LAN status

// quick check network status
BOOL CheckNetwork(void)
  { DWORD ct;
    return IsNetworkAlive(&ct) & (GetLastError() == 0); }


// wait until network is connected
BOOL WaitNetwork(BYTE Tries,BYTE Delay)
  { BYTE  rt = 0; // retry count
    while (!CheckNetwork())
      { if (++rt > Tries)
          return 0;
        Sleep(Delay * 1000); }
    return 1; }


/////////////////////////////////////////////////////////////////////////////////////////
// send datagrams
//

// compose and send datagrams
BOOL SendDatagram(PSOCKADDR To,DWORD PassCode,BYTE Command,PVOID Data,INT DataSize)
  { DATAGRAM  dgram = {0};  // blank datagram
    INT       sdgram;       // datagram size
    FD_SET    st;           // socket to be tested
    TIMEVAL   tv;           // delay time for test
    // insert passcode
    dgram.PassCode = PassCode;
    // insert command
    dgram.Command = Command;           
    // copy data
    if (DataSize > 0)
      memcpy(&dgram.Data,Data,DataSize);
    // calculate size
    sdgram = ((DWORD)&dgram.Data - (DWORD)&dgram) + DataSize + sizeof(TCHAR); 
    // wait then send
    st.fd_count    = 1;
    st.fd_array[0] = hSocket;
    tv.tv_sec      = 5;
    tv.tv_usec     = 0;
    if (select(1,NULL,&st,NULL,&tv) > 0)
      if (sendto(hSocket,(PCHAR)&dgram,sdgram,0,To,sizeof(SOCKADDR)) > 0)
        return 1;
    return 0; }

/////////////////////////////////////////////////////////////////////////////////////////
// Receive Datagrams
//

// datagram tosser prototype
BOOL CALLBACK (*Toss)(PSOCKADDR,DWORD,BYTE,LPVOID);

// receiver thread 
DWORD Listener(LPVOID DgramTosser)
  { DATAGRAM  dgram;          // blank datagram 
    INT       sdg;            // size of datagram
    SOCKADDR  from;           // return address
    INT       sf;             // size of reply addr     
    // set callback
    Toss = DgramTosser;
    // receiver loop
    while(!KillWSA)
      { // clear old data
        memset(&dgram,0,sizeof(DATAGRAM));
        // set address size
        sf = sizeof(SOCKADDR);
        // receive datagram
        sdg = recvfrom(hSocket,(PCHAR)&dgram,sizeof(DATAGRAM),0,&from,&sf);
        // hand to tosser
        if (sdg > 0)
          { Toss(&from,dgram.PassCode,dgram.Command,&dgram.Data); } }
    return WSAGetLastError(); }



// resolve server name and port to useable LAN addr
BOOL GetHostAddr(PTCHAR Name, WORD Port, PSOCKADDR Addr, BYTE Tries, BYTE Delay)
  { ADDRINFOT   hints = {0};    // hints for search
    PADDRINFOT  res   = NULL;   // pointer to search result
    BYTE        rt    = 0;      // retry count
    // wait for connection
    WaitNetwork(20,1);
    // fill in struct
    hints.ai_flags    = AI_PASSIVE;
    hints.ai_family   = AF_INET;
    hints.ai_socktype = SOCK_DGRAM;
    hints.ai_protocol = IPPROTO_UDP;
    // get ip address
    while(GetAddrInfo(Name,NULL,&hints,&res))
      { if (++rt > Tries)
          return 0; 
        Sleep(Delay * 1000); }
    // transfer to local IP struct
    memcpy(Addr,res->ai_addr,sizeof(SOCKADDR));
    ((PSOCKADDR_IN) Addr)->sin_family = AF_INET;
    ((PSOCKADDR_IN) Addr)->sin_port = htons(Port);
    // release memory 
    FreeAddrInfo(res);
    return 1; }



// for incremental port search
VOID SetHostPort(WORD Port,PSOCKADDR Addr)
  { ((PSOCKADDR_IN) Addr)->sin_port = htons(Port);
    ((PSOCKADDR_IN) Addr)->sin_family = AF_INET; }



/////////////////////////////////////////////////////////////////////////////////////////
// start and stop
//

// initialize Client port/return port number
WORD InitNetwork(WORD Port,BOOL Scan,LPVOID DgramTosser )
  { WSADATA     wsadata;              // winsock startup
    TCHAR       hn[MAX_HOSTNAME];     // host name
    DWORD       hs = MAX_HOSTNAME;    // host name size
    SOCKADDR    la;                   // local address
    INT         x = 0;                // counter
    ULONG       bl = 0;               // blocking flag
    WORD        lp = Port;            // local port
    // Load the Winsock DLL
    if (WSAStartup(MAKEWORD(2,0),&wsadata))
      return 0;
    // initialize local socket
    hSocket = socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP);
    if (hSocket == INVALID_SOCKET)
      return 0;
    // set full blocking mode
    ioctlsocket(hSocket,FIONBIO,&bl);
    // initialize localhost IP  
    GetComputerName(hn,&hs);
    if (!GetHostAddr(hn,Port,&la,10,1))
      return 0;
    // bind on user designated Port
    while(bind(hSocket,&la,sizeof(SOCKADDR)))
      { if (!Scan)
          return 0;
        SetHostPort(++lp,&la);
        if (lp > (Port + 256))
          return 0; }
    // launch the listener thread
    KillWSA = FALSE;
    hReceiver = CreateThread(NULL,0,&Listener,DgramTosser,0,NULL); 
    if (hReceiver == NULL)
      return 0;
    return lp; }



// shut down the network
VOID KillNetwork(void)
  { //let packets clear
    Sleep(100);
    // stop receiver
    KillWSA = TRUE;
    // teminate the receiver
    TerminateThread(hReceiver,0);
    // close the socket
    shutdown(hSocket,SD_BOTH);
    closesocket(hSocket);
    // let winsock close
    Sleep(100);
    // cleanup handles
    WSACleanup(); 
    CloseHandle(hReceiver); }