I want my TCP client to connect to multiple servers(each server has a separate IP and port).
I am using async_connect. I can successfully connect to different servers but the read/write fails since the server's corresponding tcp::socket object is not available.
Can you please suggest how I could store each server's socket in some data structure? I tried saving the IP, socket to a std::map, but the first server's socket object is not available in memory and the app crashes.
I tried making the socket static, but it does not help either.

Please help me!!

Also, I hope I am logically correct in making a single TCP client connect to 2 different servers. I am sharing below the simplified header & cpp file.

class TCPClient: public Socket
{
public:
    TCPClient(boost::asio::io_service& io_service,
        boost::asio::ip::tcp::endpoint ep);
    virtual ~TCPClient();
    void Connect(boost::asio::ip::tcp::endpoint ep, boost::asio::io_service &ioService, void (Comm::*SaveClientDetails)(std::string,void*),
        void *pClassInstance);
    
    void TransmitData(const INT8 *pi8Buffer);
    void HandleWrite(const boost::system::error_code& err, 
    size_t szBytesTransferred);
    void HandleConnect(const boost::system::error_code &err, 
        void (Comm::*SaveClientDetails)(std::string,void*),
        void *pClassInstance, std::string sIPAddr);
    static tcp::socket* CreateSocket(boost::asio::io_service &ioService)    
        {   return new tcp::socket(ioService); }
    static tcp::socket *mSocket;
private:
    std::string sMsgRead;
    INT8 i8Data[MAX_BUFFER_LENGTH];
    std::string sMsg;
    boost::asio::deadline_timer mTimer;
};

tcp::socket* TCPClient::mSocket = NULL;

TCPClient::TCPClient(boost::asio::io_service &ioService,
        boost::asio::ip::tcp::endpoint ep) :
        mTimer(ioService)
{
}

void TCPClient::Connect(boost::asio::ip::tcp::endpoint ep, 
        boost::asio::io_service &ioService, 
        void (Comm::*SaveServerDetails)(std::string,void*),
        void *pClassInstance)
{
    mSocket = CreateSocket(ioService);
    std::string sIPAddr = ep.address().to_string();
    /* To send connection request to server*/
    mSocket->async_connect(ep,boost::bind(&TCPClient::HandleConnect, this,
            boost::asio::placeholders::error, SaveServerDetails,
            pClassInstance, sIPAddr));
}

void TCPClient::HandleConnect(const boost::system::error_code &err,
        void (Comm::*SaveServerDetails)(std::string,void*),
        void *pClassInstance, std::string sIPAddr)
{
    if (!err)
    {
        Comm* pInstance = (Comm*) pClassInstance;
        if (NULL == pInstance) 
        {
            break;
        }
        (pInstance->*SaveServerDetails)(sIPAddr,(void*)(mSocket));
    }
    else
    {
        break;
    }
}

void TCPClient::TransmitData(const INT8 *pi8Buffer)
{
    sMsg = pi8Buffer;
    if (sMsg.empty()) 
    {
        break;
    }
    mSocket->async_write_some(boost::asio::buffer(sMsg, MAX_BUFFER_LENGTH),
            boost::bind(&TCPClient::HandleWrite, this,
                    boost::asio::placeholders::error,
                    boost::asio::placeholders::bytes_transferred));
}

void TCPClient::HandleWrite(const boost::system::error_code &err,
        size_t szBytesTransferred) 
{
        if (!err) 
        {
            std::cout<< "Data written to TCP Client port! ";
        } 
        else 
        {
            break;
        }
}

CodePudding user response：

You seem to know your problem: the socket object is unavailable. That's 100% by choice. You chose to make it static, of course there will be only one instance.

Also, I hope I am logically correct in making a single TCP client connect to 2 different servers.

It sounds wrong to me. You can redefine "client" to mean something having multiple TCP connections. In that case at the very minimum you expect a container of tcp::socket objects to hold those (or, you know, a Connection object that contains the tcp::socket.

BONUS: Demo

For fun and glory, here's what I think you should be looking for.

Notes:

• no more new, delete
• no more void*, reinterpret casts (!!!)
• less manual buffer sizing/handling
• no more bind
• buffer lifetimes are guaranteed for the corresponding async operations
• message queues per connection
• connections are on a strand for proper synchronized access to shared state in multi-threading environments
• I added in a connection max idle time timeout; it also limits the time taken for any async operation (connect/write). I assumed you wanted something like this because (a) it's common (b) there was an unused deadline_timer in your question code

Note the technique of using shared pointers to have Comm manage its own lifetime. Note also that _socket and _outbox are owned by the individual Comm instance.