socket chat application i.e i want to chat with multiple clients at a time?

I am working on socket chat application, i.e I want to chat with multiple clients at a time. I have written the folllowing program. The server accepts multiple clients, but I am able to chat with only latest client. I am not able chat with previous client, can someone explain to me why?

/* tcpserver.c */

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <pthread.h>

void *thread(int *);

int main()
{
        int sock, connected, true = 1,n=1; 
    pthread_t tid;
        struct sockaddr_in server_addr,client_addr;   
        int sin_size;

        if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
            perror("Socket");
            exit(1);
        }

        if (setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&true,sizeof(int)) == -1) {
            perror("Setsockopt");
            exit(1);
        }

        server_addr.sin_family = AF_INET;        
        server_addr.sin_port = htons(5000);    
        server_addr.sin_addr.s_addr = INADDR_ANY;
        bzero(&(server_addr.sin_zero),8);

        if (bind(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr))
                                                                       == -1) {
            perror("Unable to bind");
            exit(1);
        }

        if (listen(sock, 5) == -1) {
            perror("Listen");
            exit(1);
        }

    printf("\nTCPServer Waiting for client on port 5000");
        fflush(stdout);


        while(n<=5)
        { 

            sin_size = sizeof(struct sockaddr_in);

            connected = accept(sock, (struct sockaddr *)&client_addr,&sin_size);

            printf("\n I got a connection from (%s , %d)",
                   inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port));
        pthread_create(&tid,NULL,thread,&connected);
        n++;
    }

      close(sock);
      return 0;
}


void *thread(int *nfd)
{
        char send_data [1024] , recv_data[1024];      
        int bytes_recieved;   
        while (1)
            {
              printf("\n SEND (q or Q to quit) : ");
              gets(send_data);

              if (strcmp(send_data , "q") == 0 || strcmp(send_data , "Q") == 0)
              {
                send(*nfd, send_data,strlen(send_data), 0);
                close(nfd);
                break;
              }

              else
                 send(*nfd, send_data,strlen(send_data), 0); 

              bytes_recieved = recv(*nfd,recv_data,1024,0);

              recv_data[bytes_recieved] = '\0';

              if (strcmp(recv_data , "q") == 0 || strcmp(recv_data , "Q") == 0)
              {
                close(*nfd);
                break;
              }

              else
              printf("\n RECIEVED DATA = %s " , recv_data);
              fflush(stdout);
            }

}







/* tcpclient.c */

#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>


int main()

{

        int sock, bytes_recieved; 
        char send_data[1024],recv_data[1024];
        struct hostent *host;
        struct sockaddr_in server_addr; 

        host = gethostbyname("127.0.0.1");

        if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
            perror("Socket");
            exit(1);
        }

        server_addr.sin_family = AF_INET;    
        server_addr.sin_port = htons(5000);  
        server_addr.sin_addr = *((struct in_addr *)host->h_addr);
        bzero(&(server_addr.sin_zero),8);

        if (connect(sock, (struct sockaddr *)&server_addr,
                    sizeof(struct sockaddr)) == -1)
        {
            perror("Connect");
            exit(1);
        }

        while(1)
        {

          bytes_recieved=recv(sock,recv_data,1024,0);
          recv_data[bytes_recieved] = '\0';

          if (strcmp(recv_data , "q") == 0 || strcmp(recv_data , "Q") == 0)
          {
           close(sock);
           break;
          }

          e开发者_如何学Golse
           printf("\nRecieved data = %s " , recv_data);

           printf("\nSEND (q or Q to quit) : ");
           gets(send_data);

          if (strcmp(send_data , "q") != 0 && strcmp(send_data , "Q") != 0)
           send(sock,send_data,strlen(send_data), 0);

          else
          {
           send(sock,send_data,strlen(send_data), 0);  
           close(sock);
           break;
          }

        }  
return 0;
}

---

Other post will help you debug the current error. This advice will hopefully save you time and patience if you decide to expand the project instead of a basic server - client model.

The advice is: Don't use threads. Poll() takes a lot of resources. Use select().

Threads should be used when you really need to use them. John Ousterhout illustrated this a long time ago and for some reason I always remember it when people are lost debugging basic thread behaviour.

---

(Not really an answer:) You should only use multiple threads when you want to force a multi-processor machine into using its different processors simultaneously. For instance, when drawing a complicated mathematical graph, you may well split the graph into several parts so each processor can calculate a different part of it simulatenously. Many may disagree but if you need to multi-thread because you want to unblock I/O you're doing it wrong.

Here, you want to multi-thread simply because you want to unblock I/O. One simpler way is to fork() the server into child processes that perform a simple write of the message to their designated sockets.
A better way is multi-casting as mentioned by Alastair. But multi-casting can also be done poorly. This is a good text on it

---

This is a trick question, right?

You're passing the address of "connected" to the thread, not the value. As soon as a new connection comes in the value gets overwritten and you end up with two threads talking to the same connection.

Incidentally, why are you using multi-threading? poll() is a better solution. You should easily be able to build a server that handles multiple clients with a single thread. It really isn't difficult.

Also if you want a true multi-person chat application, look into multi-casting. It means you only need to write a message once, not multiple times, once per socket. I haven't done any multi-casting myself, so can't tell you any more than that.