My C Chat Program is unable to communicate.

mcp_achindra · 03-20-2004, 01:10 AM

I have written a code in c to work on Linux. I m looking to write a program to chat, but being a newbie in this field, I am facing problems. Please help me with that. All I want to design is a wall like command. A server to listen for connections, and echos back the message to all the connected clients. The most gruesome prob;lem I m facing is to make my server listen for multiple connections through a single port, because I can't ask all the clients to connect to different ports. Help me with some working code, I can learn from. If any one could give me the code to simply accept the connection and echo back whatever a client has sent and the welcome message. To the best if any one can help me use the same port for multiple connecions.

Server Code ......

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

#define DestIP "127.0.0.1"
#define SourcePort 12004

char *msg = "Hello World !";

main ()
{
int sockfd;
struct sockaddr_in source_addr;

if ((sockfd = socket (AF_INET, SOCK_STREAM, 0)) == -1)
{
printf ("Cannot create socket !\n");
exit (-1);
}

source_addr.sin_family = AF_INET;
source_addr.sin_port = htons(SourcePort);
source_addr.sin_addr.s_addr = htonl(INADDR_ANY);
memset (&(source_addr.sin_zero), '\0', 8);

if (bind (sockfd, (struct sockaddr *) &source_addr, sizeof(struct sockaddr))== -1)
{
printf ("Unable to bind connection to the OS.");
exit(-1);
}

for (;

{
msg = "";
recv (sockfd, msg, sizeof (msg), 0);
printf ("%s", msg);
}
}

________________________________________________________________________

Client Code:......

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

#define DestIP "127.0.0.1"
#define DestPort 12004

char *msg="Hello World !";

main()
{
int sockfd;
struct sockaddr_in dest_addr;

if (sockfd=socket(AF_INET,SOCK_STREAM,0)==-1)
{
printf("Cannot create socket !\n");
exit(-1);
}

dest_addr.sin_family=AF_INET;
dest_addr.sin_port=htons(DestPort);
dest_addr.sin_addr.s_addr=inet_addr(DestIP);
memset(&(dest_addr.sin_zero),'\0',8);

if ((connect(sockfd,(struct sockaddr *)&dest_addr, sizeof(struct sockaddr)))==-1)
{
printf("Unable to connect to remote host !");
exit(-1);
}

if (send(sockfd, msg, sizeof(msg),0)==-1)
{
printf("Error sending data...");
exit(-1);
}

}

________________________________________________________________________

Please help me write a better code.

deiussum · 03-20-2004, 10:04 AM

I didn't look too closely at your code, but for what you want you only need to create a single listen socket on a single port. Each accept() you do returns a new socket that you use for the communication. The listen socket remains, and you can do further accepts on it.

As a general idea of how I would structure your program, here's a bit of pseudo code for you.

Code:

int main()
{
       int listenSock = CreateListenSocket(4444); // made-up function to create and bind a listen socket
       int clientSock;
       SocketList clientList; // made-up object to store list of sockets

       while(1)
       {
             if (PendingAccept(listenSock))
             {
                  clientSock = accept(listenSock);
                  clientList.Add(clientSock);
             }

             for (all clients in list)
             {
                 int client = GetClientFromListSomehow();
                 if (CanRecv(client))
                 {
                      int bytesRecvd = recv(client);

                      if (bytesRecvd == 0) // client disconnected
                      {
                           clientList.Remove(client);
                      }
                      else
                      {
                           for (each client in client list)
                           {
                                send(receivedText);
                           }
                      }
                 }
             }
       }
}

To check if there are pending accepts, or data that can be read from a socket, you can use the fd_set stuff. Checking if a listen socket can "receive" without blocking is how you check if you can successfully accept a socket connection.

Hope that helps. As I said, it's pseudo code, so you have to fill in a lot of the details, but hopefully it gives you an idea of how you can structure your code.

Edit: Looked at the code a bit more. You are missing 2 major steps in your server code.
1. You must set the socket to a listen state with the listen function.
2. You must accept a connection with the accept function.