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This article mainly introduces "how to realize simple chat room with Select multiplexing under Linux". In daily operation, I believe that many people have doubts about how to realize simple chat room with Select multiplexing under Linux. Xiaobian consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts about "how to realize simple chat room with Select multiplexing under Linux". Next, please follow the editor to study!

Preface

There are similarities and differences with the previous udp chat room. This time, our client send is an encapsulated packet, recv is a string, the server recv is a packet, and send is a string. When the user connects, a login request is sent, then the server processes it and broadcasts it to other clients.

The principle of Multiplexing

Basic concept

Multiplexing means that multiple descriptors can be monitored through a mechanism, and once a descriptor is ready (usually read-ready or write-ready), the program can be informed to read and write accordingly. It's actually an asynchronous operation, waiting for a runnable descriptor.

Compared with multi-process and multi-thread technology, the biggest advantage of Icano multiplexing technology is that the system overhead is small, the system does not need to create processes / threads, and does not have to maintain these processes / threads, thus greatly reducing the system overhead.

There are generally three ways to implement multiplexing:

Select

Poll

Epoll

This code mainly shows the usage of select:

Selectint select (int nfds, fd_set * readfds, fd_set * writefds, fd_set * exceptfds, struct timeval * timeout)

This is the select statement given in Linux's man manual.

The first parameter, ndfs

The first parameter is nfds, which represents the largest file descriptor + 1 in the file description collection, because the traversal of select is used by [0MagneNfds)

The second parameter, readfds

Readfds represents a collection of read events

The third parameter, writefds

Writefds represents a collection of read events

The fourth parameter exceptfds

Exceptfds represents a collection of exception parameters

The fifth parameter timeout

Indicates a timeout, and timeout tells the kernel how long it can take to wait for any one of the specified descriptions to be ready. Its timeval structure is used to specify the number of seconds and microseconds during this period.

Struct timeval {long tv_sec; / / second long tv_usec; / / microseconds} fd_set

The definition of the fd_set structure actually contains an array of fds_bits bits, and each element of the array is marked with a file descriptor of a fixed size, specified by FD_SETSIZE. In general, the size of FD _ SETSIZE is 1024.

All we need to care about is how to use it:

The following functions are functions that operate on fd_set

Void FD_ZERO (fd_set * fdset); / / empty the collection void FD_SET (int fd, fd_set * fdset); / / add a given file descriptor to the collection void FD_CLR (int fd, fd_set * fdset); / / remove a given file descriptor from the collection int FD_ISSET (int fd, fd_set * fdset) / / check whether the file descriptor specified in the collection can read and write to the server Code

The functions implemented are:

When the client connects to the client, the server broadcasts to other clients.

Send a message to the server, and then the server broadcasts it online to other clients

The client exits and the server broadcasts to other clients

# include # define N 1024int FD [FD _ SETSIZE]; / / set of users, char type;// message type char name [20]; char text [N]; / / message content} MSG;typedef struct User {int fd; struct User * next;} USE;USE * head USE* init () {USE* p = (USE*) malloc (sizeof (USE)); memset (preco 0USE* Sizeof (USE)); p-> next = NULL; return p;} void Link (int new_fd) {/ / add new connections to the user list USE* p = head; while (p-> next) {pprecp-> next;} USE* k = (USE*) malloc (sizeof (USE)) K-> fd = new_fd; k-> next = NULL; p-> next = k;} void login (int fd,MSG msg) {USE * p = head; char buf [Niss30]; strcpy (buf,msg.name); strcat (buf, "online! Come and play with me! ") ; printf ("fd =% d% s\ n", fd,buf); while (p-> next) {/ / send online message if (fd! = p-> next- > fd) send (p-> next- > fd,&buf,sizeof (buf), 0); p = p-> next;} / / puts ("Over login") } void chat (int fd,MSG msg) {/ / printf ("% d\ n", msg.text [0]); if (strcmp (msg.text, "\ n") = = 0) return; USE * p = head; char buf [Niss30]; strcpy (buf,msg.name); strcat (buf, ":"); strcat (buf,msg.text); printf ("% s\ n", buf) While (p-> next) {/ / send messages to other users if (fd! = p-> next- > fd) send (p-> next- > fd,&buf,sizeof (buf), 0); p = p-> next;}} void quit (int fd,MSG msg) {USE * p = head; char buf [Niss30]; strcpy (buf,msg.name); strcat (buf, "sadly quit group chat!") ; printf ("% s\ n", buf); while (p-> next) {/ / send online information if (fd! = p-> next- > fd) send (p-> next- > fd,&buf,sizeof (buf), 0); p = p-> next Initialize the TCP server and return the server's socket descriptor * * / int init_tcp_server (unsigned short port) {int ret; int opt; int listen_fd; struct sockaddr_in self; / / listening descriptor listen_fd = socket (AF_INET, SOCK_STREAM, 0); if (listen_fd)

< 0) { perror("socket"); return -1; } // 配置监听描述符地址复用属性 opt = 1; ret = setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR,&opt, sizeof(opt)); if (ret < 0) { perror("set socket opt"); return -1; } // 填充服务器开放接口和端口号信息 memset(&self, 0, sizeof(self)); self.sin_family = AF_INET; self.sin_port = htons(port); self.sin_addr.s_addr = htonl(INADDR_ANY); ret = bind(listen_fd, (struct sockaddr *)&self, sizeof(self)); if (ret == -1) { perror("bind"); return -1; } // 默认socket是双向，配置成监听模式 listen(listen_fd, 5); return listen_fd;}// 监听处理器int listen_handler(int listen_fd) { int new_fd; new_fd = accept(listen_fd, NULL, NULL); if (new_fd < 0) { perror("accpet"); return -1; } return new_fd;}// 客户端处理器int client_handler(int fd) { int ret; MSG msg; // 读一次 ret = recv(fd, &msg, sizeof(MSG), 0);//读取消息// printf("name = %s\n",msg.name); if (ret < 0) { perror("recv"); return -1; } else if (ret == 0) {//断开连接 quit(fd,msg); return 0; } else {//数据处理 if(msg.type == 'L') {//登陆处理 login(fd,msg); } else if(msg.type == 'C') {//聊天处理 chat(fd,msg); } else if(msg.type == 'Q') {//退出处理 quit(fd,msg); } }// puts("Over client_handler"); return ret;}// 标准输入处理器int input_handler(int fd) { char buf[1024]; fgets(buf, sizeof(buf), stdin); buf[strlen(buf) - 1] = 0; printf("user input: %s\n",buf); return 0;}void main_loop(int listen_fd) { fd_set current, bak_fds; int max_fds; int new_fd; int ret; // 把监听描述符、标准输入描述符添加到集合 FD_ZERO(¤t); FD_SET(listen_fd, ¤t); FD_SET(0, ¤t); max_fds = listen_fd; while (1) { bak_fds = current; // 备份集合 ret = select(max_fds+1, &bak_fds, NULL, NULL, NULL); if (ret < 0) { perror("select"); break; } // 判断内核通知哪些描述符可读，分别处理 for (int i = 0; i = FD_SETSIZE) { printf("客户端连接过多！"); close(new_fd); continue; } // 正常连接更新系统的集合，更新系统的通信录 Link(new_fd);//将新的连接描述符放进链表里面 FD_SET(new_fd, ¤t); max_fds = new_fd >

Max_fds? New_fd: max_fds;} else {/ / New connection descriptor readable recv ret = client_handler (I); if (ret

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