Question

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Detect When Network Cable Unplugged

I would need some help to check if somebody disconnected. At the moment my code says that somebody disconnected every time I connect to it. I tried to use send() to check if they are still “alive” but I’m not sure if I did it right.

#pragma comment (lib,"Ws2_32.lib")

#include <iostream>
#include <WinSock2.h>

using namespace std;

#pragma region shittyvars

int countcons = 0, connections[100];
char *dead = new char;
int error;
WSAData netinfo;
int mySocket;
HANDLE acceptth, discth;

#pragma endregion

void AcceptThread( int* a)
{
int clientSocket;
while ( (clientSocket = accept(mySocket,0,0))!=SOCKET_ERROR) 
   connections[countcons++]=clientSocket;
}
void DissconectThread(int*b)
{
for(;;)
  for(int i=0;i<countcons;i++)
   {
       error = send(connections[i],dead,4,0);
 error = WSAGetLastError();
       if(error != 0 )
       {
           closesocket(connections[i]);
           for(int j=i+1 ; j<countcons ;j++)
               connections[j-1]=connections[j];
           countcons--;
           cout<<"\nSomebody disconnected\n";
       }
   }
}

int main() {
#pragma region InitConnection
    error = WSAStartup(MAKEWORD(2,2), &netinfo);

    if (error == SOCKET_ERROR) {
        cout << "Error:Starting socket failed";
        return 1;
    }

    mySocket = socket(AF_INET, SOCK_STREAM, 0);

    if (mySocket == SOCKET_ERROR) {
        cout << "Error:Socket failed to initialize!";
        return 1;
    }
    cout << "Works!";

    struct sockaddr_in server; // network socket struct

    server.sin_family = AF_INET;
    server.sin_port = htons(7654);
    server.sin_addr.s_addr = INADDR_ANY; // Let's us accept any connection

    error = bind(mySocket, (sockaddr*) &server, sizeof(server));

    if (error == SOCKET_ERROR) {
        cout << "Error:Failed to bind socket";
        return 1;
    }

    error = listen(mySocket, 100);

    if (error == SOCKET_ERROR) {
        cout << "Error:The socket is deaf";
        return 1;
    }

#pragma endregion

    acceptth = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE) AcceptThread,
            &server, 0, (LPDWORD) &acceptth);
    discth = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE) DissconectThread,
            &server, 0, (LPDWORD) &discth);
    getchar();
    closesocket(mySocket);
    WSACleanup();
    getchar();
    return 0;
}

How do I solve this problem?

Answer 1

Check the error you get when the send fails… it might point you in the right direction (use WSAGetLastError() on Windows). Incidentally, your DissconectThread will just spin and chew CPU until there’s a connection, then it will jam out data until it blocks on one connection with a full send buffer… probably not what you intended.