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How to write broadcast message using MFC

HI Expert,

I'm writing a MFC program and want to detect all the nodes in one subnet.

I know a boradcast message will let me get  replys from all the nodes in this subnet. But, how can I send a boradcast message in VC++. (Put the taget address as a broadcast address)).

And how could I handle a lot of replies which might come almost together?


1 Solution
1. Derive a new class from CAsyncSocket. Lets call CMySocket.
2. Open this socket allow transmission of brodcast packets.
3. Generate a unique identifyer for the session and store for the life of the app.

CMySocket   sock;
UUID        uuid;
UINT        nPort = 999;    // Use another port number if you like

BOOL CMyApp::OnInitInstance()


    VERIFY(sock.Create(nPort, SOCK_DGRAM, FD_READ));
    BOOL bTrue = TRUE;
    VERIFY(sock.SetSockOpt(SO_BROADCAST, &bTrue, sizeof(bTrue)));


    return TRUE;

4. Override OnReceive function in CMySocket. This function will be called every
   time a packet is ready to be received.

extern UUID uuid;
extern UINT nPort;

void CMySocket::OnReceive(int nErrorCode)
    char sz[1024];

    CString strFromAddr;
    UINT    nFromPort;

    int nLen = ReceiveFrom(sz, 256, strFromAddr, nFromPort);
    if(nLen != SOCKET_ERROR)
        sz[nLen] = 0;
        TRACE("Received: '%s' from %s:%d\n", sz, strFromAddr, nFromPort);

        // When we receive a PING then reply with: PONG,<computer name>,<uuid>
        if(!_strnicmp(sz, "PING", 4))
            unsigned char* pszUUID = NULL;
            char szName[256];
            DWORD dw = sizeof(szName);
            GetComputerName(szName, &dw);

            UuidToString(&uuid, &pszUUID);

            CString s;
            s.Format("PONG,%s,%s", szName, pszUUID);
            VERIFY(SendTo(s, s.GetLength(), nPort));


            SendTo(s, s.GetLength(), nFromPort, strFromAddr);
        else if(!_strnicmp(sz, "PONG", 4))
            TRACE("Found node at %s:%d\n", strFromAddr, nFromPort);

            char *pToken = strtok(sz, ",");

            pToken = strtok(NULL, ",");
            TRACE("ComputerName: %s\n", pToken);

            pToken = strtok(NULL, ",");
            TRACE("UUID:         %s\n", pToken);
            // TODO: process other commands

5. Now to enummerate nodes on the netword execute this code

sock.SendTo("PING", 4, nPort);


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