#include <sys/types.h>#include <sys/socket.h>#include <stdio.h>#include <netinet/in.h>#include <sys/time.h>#include <sys/ioctl.h>#include <unistd.h>#include <stdlib.h>int main(){    int server_sockfd, client_sockfd;    int server_len, client_len;    struct sockaddr_in server_address;    struct sockaddr_in client_address;    int result;    fd_set readfds, testfds;    server_sockfd = socket(AF_INET, SOCK_STREAM, 0);    server_address.sin_family = AF_INET;    server_address.sin_addr.s_addr = htonl(INADDR_ANY);//允许任何ip连接    server_address.sin_port = htons(9734);    server_len = sizeof(server_address);    bind(server_sockfd, (struct sockaddr*)&server_address, server_len);    listen(server_sockfd, 5);    FD_ZERO(&readfds);    FD_SET(server_sockfd, &readfds);//将监听套接字放到可读集合中    while(1){        char ch;        int fd;        int nread;        testfds = readfds;        printf("server waiting\n");        result = select(FD_SETSIZE, &testfds,  (fd_set*)0, (fd_set*)0, (struct timeval*)0);//时间指针为0：表示一直阻塞，如果返回小于1表示程序出错        if(result < 1){            perror("server5");            exit(1);        }        for(fd = 0; fd < FD_SETSIZE; ++fd){            if(FD_ISSET(fd, &testfds)){                if(fd == server_sockfd){//监听套接字可读表示，有新连接                    client_len = sizeof(client_address);                    client_sockfd = accept(server_sockfd, (struct sockaddr*)&client_address, &client_len);                    FD_SET(client_sockfd, &readfds);//将客户端套接字放到可读集合中                    printf("adding client on fd %d\n", client_sockfd);                }else{                    ioctl(fd, FIONREAD, &nread);                    if(nread == 0){//读到0字节表示客户端断开socket                        close(fd);                        FD_CLR(fd, &readfds);//将套接字从集合中清除                        printf("removing client on fd %d\n", fd);                    }else{                                            read(fd, &ch, 1);                        sleep(5);                        printf("serving cient on fd  %d\n", fd);                        ch++;                        write(fd, &ch, 1);                    }                }            }        }    }}