select server

server with select

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

 #define ERR_EXIT(m) \
     do { \
         perror(m); \
         exit(EXIT_FAILURE); \
     } while ()

 int main(void)
 {

     signal(SIGPIPE, SIG_IGN);
     int listenfd; //被动套接字(文件描述符），即只可以accept, 监听套接字
     if ((listenfd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < )
 //  listenfd = socket(AF_INET, SOCK_STREAM, 0)
         ERR_EXIT("socket error");

     struct sockaddr_in servaddr;
     memset(&servaddr, , sizeof(servaddr));
     servaddr.sin_family = AF_INET;
     servaddr.sin_port = htons();
     servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
     /* servaddr.sin_addr.s_addr = inet_addr("127.0.0.1"); */
     /* inet_aton("127.0.0.1", &servaddr.sin_addr); */

     int on = ;
     if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < )
         ERR_EXIT("setsockopt error");

     if (bind(listenfd, (struct sockaddr*)&servaddr,sizeof(servaddr)) < )
         ERR_EXIT("bind error");

     if (listen(listenfd, SOMAXCONN) < ) //listen应在socket和bind之后，而在accept之前
         ERR_EXIT("listen error");

     struct sockaddr_in peeraddr; //传出参数
     socklen_t peerlen = sizeof(peeraddr); //传入传出参数，必须有初始值

     int conn; // 已连接套接字(变为主动套接字，即可以主动connect)
     int i;
     int client[FD_SETSIZE];
     int maxi = ; // client数组中最大不空闲位置的下标
     for (i = ; i < FD_SETSIZE; i++)
         client[i] = -;

     int nready;
     int maxfd = listenfd;
     fd_set rset;
     fd_set allset;
     FD_ZERO(&rset);
     FD_ZERO(&allset);
     FD_SET(listenfd, &allset);

     while () {
         rset = allset;
         nready = select(maxfd + , &rset, NULL, NULL, NULL);
         if (nready == -) {
             if (errno == EINTR)
                 continue;
             ERR_EXIT("select error");
         }

         if (nready == )
             continue;

         if (FD_ISSET(listenfd, &rset)) {

             conn = accept(listenfd, (struct sockaddr*)&peeraddr, &peerlen);  //accept不再阻塞
             if (conn == -)
                 ERR_EXIT("accept error");

             for (i = ; i < FD_SETSIZE; i++) {
                 if (client[i] < ) {
                     client[i] = conn;
                     if (i > maxi)
                         maxi = i;
                     break;
                 }
             }

             if (i == FD_SETSIZE) {
                 fprintf(stderr, "too many clients\n");
                 exit(EXIT_FAILURE);
             }

             printf("recv connect ip=%s port=%d\n", inet_ntoa(peeraddr.sin_addr),
                 ntohs(peeraddr.sin_port));

             FD_SET(conn, &allset);
             if (conn > maxfd)
                 maxfd = conn;

             if (--nready <= )
                 continue;
         }

         for (i = ; i <= maxi; i++) {
             conn = client[i];
             if (conn == -)
                 continue;

             if (FD_ISSET(conn, &rset)) {

                 char recvbuf[] = {};
                 int ret = read(conn, recvbuf, );
                 if (ret == -)
                     ERR_EXIT("readline error");
                 else if (ret  == ) { //客户端关闭
                     printf("client close \n");
                     FD_CLR(conn, &allset);
                     client[i] = -;
                     close(conn);
                 }

                 fputs(recvbuf, stdout);
                 write(conn, recvbuf, strlen(recvbuf));

                 if (--nready <= )
                     break;
             }
         }

     }

     return ;
 }

ref1      ref2