Single server for multiple clients (chat) in C

See more:

C

server

multi-threading

sockets

I wrote a server-client chat for Windows (using threads and non-blocking socket), it works fine with single server but still not supports a few clients. Server works like echo (but only for last connected client). Client.c uses CreateThread function and non-blocking sockets.

I made 3 functions to keep socket values of connected clients in the list, print them and remove when client has left. It works fine:

    struct listElement
{
    SOCKET socket;
    struct listElement *next;
};

struct clientList
{
    struct listElement* head;
};

/*my implementation function, print and remove*/
int pushBackClient(struct clientList *list, SOCKET socket)
void print(struct clientList *list)
int removeFromList(struct clientList *list, SOCKET socket)

Well, this part is done. Now I can collect sockets of every connected client, when client has disconnected its socket is also removed.

But there is still no multiclient support. How should I realise that? I think my code is needed to change a few strings to reach my porpose. And the next question follows from the last: how should orginize my server to send echo-message to ALL the clients except the client who has sent the message?

What I have tried:

server.c

    /* before this cycle there are socket(), listen() and bind() functions */
	while (1)
			{
				FD_ZERO(&readSet);
				FD_SET(listeningSocket, &readSet);
			
				if (newSocketDescriptor)
				{
					FD_SET(newSocketDescriptor, &readSet);
				}
			
				tv.tv_sec = 5;
				retVal = select(listeningSocket + 1, &readSet, NULL, NULL, 0);
				if (retVal == SOCKET_ERROR)
				{
					printf("Select error");
					break;
				}
				else if (retVal == 0)
				{
					printf(". . .\n");
					continue;
				}
				else
				{
					if ((FD_ISSET(listeningSocket, &readSet)) != 0)
					{
						if ((newSocketDescriptor = accept(listeningSocket, (struct sockaddr *)&clientAddr, &clientAddrSize)) == SOCKET_ERROR)
						{
							printf("Accept error ");
							break;
						}
						/* newSocketDescriptor - new connected client, then implement the list */
						pushBackClient(&clientList, newSocketDescriptor);
						print(&clientList);

						FD_ZERO(&readSet);
						FD_SET(newSocketDescriptor, &readSet);
						nclients++; 
						PRINTUSERS

						HOSTENT *hst = gethostbyaddr((const char *)&serverAddr.sin_addr.s_addr, 4, AF_INET);
						printf("Welcome %s (%s:%d) new connected\n", hst->h_name, inet_ntoa(clientAddr.sin_addr), ntohs(clientAddr.sin_port));
					}
				
					// READ
					if (FD_ISSET(newSocketDescriptor, &readSet) != 0)
					{
						if ((numBytes = recv(newSocketDescriptor, &bufferData[0], sizeof(bufferData), 0)) == SOCKET_ERROR)
						{
								printf("Recv failed\n");
								break;
						}
						else
						{
							if (!strcmp(&bufferData[0], "quit\n"))
							{
								removeFromList(&clientList, newSocketDescriptor); // if server gets "quit" - remove socket from the list
								newSocketDescriptor = 0;
								nclients--; PRINTUSERS
								printf("Recv failed\n");
								printf("It seems client (%s:%d) has disconnected\n", inet_ntoa(clientAddr.sin_addr), ntohs(clientAddr.sin_port));
								FD_ZERO(&readSet);
							}
							else
							{
								bufferData[numBytes] = '\0';
								Sleep(250);
								printf("Client -> Server: %s", &bufferData[0]);
								FD_ZERO(&writeSet);
								FD_SET(newSocketDescriptor, &writeSet);
							}
						}
					}
					// WRITE (send)
					if (FD_ISSET(newSocketDescriptor, &writeSet) != 0)
					{
						if (send(newSocketDescriptor, &bufferData[0], strlen(&bufferData[0]), 0) == SOCKET_ERROR)
						{
							printf("Send error");
							break;
						}
						bufferData[numBytes] = '\0';
						Sleep(250);
						printf("Server -> Client: %s", &bufferData[0]);
					}
				}
			}

Thanks for attention and advices