Socket programming chat application-CodePudding

I made a chat application using sockets in c language. When i run server and client on same device it works fine. But, when i run client and server on different device client shows connect error. is this problem related to ip address.

client side:

int main(int argc, char **argv){
    if(argc != 2){
        printf("Usage: %s <port>\n", argv[0]);
        return EXIT_FAILURE;
    }

    char *ip = "152.168.0.100";
    int port = atoi(argv[1]);

    signal(SIGINT, catch_ctrl_c_and_exit);

    printf("Please enter your name: ");
  fgets(name, 32, stdin);
  str_trim_lf(name, strlen(name));


    if (strlen(name) > 32 || strlen(name) < 2){
        printf("Name must be less than 30 and more than 2 characters.\n");
        return EXIT_FAILURE;
    }

    struct sockaddr_in server_addr;

    /* Socket settings */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
  server_addr.sin_family = AF_INET;
  server_addr.sin_addr.s_addr = inet_addr(ip);
  server_addr.sin_port = htons(port);


  // Connect to Server
  int err = connect(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr));
  if (err == -1) {
        printf("ERROR: connect\n");
        return EXIT_FAILURE;
    }

server side:

int main(int argc, char **argv){
    if(argc != 2){
        printf("Usage: %s <port>\n", argv[0]);
        return EXIT_FAILURE;
    }

    char *ip = "127.0.0.1";
    int port = atoi(argv[1]);
    int option = 1;
    int listenfd = 0, connfd = 0;
  struct sockaddr_in serv_addr;
  struct sockaddr_in cli_addr;
  pthread_t tid;

  /* Socket settings */
  listenfd = socket(AF_INET, SOCK_STREAM, 0);
  serv_addr.sin_family = AF_INET;
  serv_addr.sin_addr.s_addr = inet_addr(ip);
  serv_addr.sin_port = htons(port);

CodePudding user response：

So as far as I can tell, the codes that you posted are incomplete, but let's assume that, as you say, everything is working fine, it work in the local machine, but when you run the two programs in two different devices, the client fails to connect to the server.

Then I would ask you the question, as I also asked it in the comment: are the two devices in the same subnet? You have a home router, and both devices are connected to this router?

If not, then that will be the problem. I am not sure how deep you understand IP addresses and subnets, but here is a simple summary. When you look at the IP address on your PC, you see your private IP address that was given you by the router. Let's say, that you have two machines connected to the same router, one has the IP address of 192.168.0.101, the other 192.168.0.102. If 192.168.0.101 is the client and wants to connect to the server that runs on 192.168.0.102, it should work without problems.

But let's say that you send the server code to me. I run the server on my computer, which has the IP address of 192.168.0.103, you still run the client at home on 192.168.0.101. In this case, you won't be able to connect to my machine, because the 192.168.0.103 is the private IP address given out by my own router. For that to work, I would have to at least configure my router to open up a port and forward the packets coming to that port to my PC. Then I would have to give you the public IP and the port. And so if the firewall is configured so that it allows your packets into my network, then it might work.

Of course it is a bit more complicated than this, but this is the general idea.

If this is not the case for you, and the devices are on the same subnet, then we would simply need more information and the comlete code.