//

include <stdio.h>
include <stdlib.h>
include <unistd.h>
include <string.h>
include <sys/types.h>
include <sys/socket.h>
include <netinet/in.h>
include <arpa/inet.h>
include <errno.h>
include <sys/select.h>
define MAXUSERS 5
define BUFFER_SIZE 64
define FD_LIMIT 65535
int USERS[MAXUSERS];
int user_count = 0;
void showclient()
{
    int i;
    printf("user_count: %d\n", user_count);
    for (i = 0; i < MAXUSERS; i++) {
        printf("[%d]:%d  ", i, USERS[i]);
    }
    printf("\n\n");
}
int main(int argc, const char * argv[])
{

struct sockaddr_in server_addr;
struct sockaddr_in client_addr;

socklen_t client_addrlength = sizeof(client_addr);


bzero(&server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(33333);
server_addr.sin_addr.s_addr = htonl(INADDR_ANY);

//創建
int sock_fd = socket( PF_INET, SOCK_STREAM, 0 );
if (sock_fd<0) {
    printf("socket error:%d",errno);
    close(sock_fd);
    exit(1);
}


int yes = 1;
if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
    perror("setsockopt");
    exit(1);
}


int sret;

//綁定
sret = bind( sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr) );
if (sret<0) {
    printf("bind error:%d",errno);
    close(sock_fd);
    exit(2);
}

//監聽
sret = listen(sock_fd, MAXUSERS);
if (sret<0) {
    printf("listen error:%d",errno);
    close(sock_fd);
    exit(3);
}
printf("start ok, listen port:%d\n", ntohs(server_addr.sin_port));

char buf[1024];
int maxsock = sock_fd;


fd_set read_fds;        //可讀
ssize_t ret;

while (1) {

    FD_ZERO(&read_fds);
    FD_SET(sock_fd, &read_fds);

    //需要監聽的集合
    for (int i =0; i<user_count; i++) {
        if (USERS[i] != 0) {
            FD_SET(USERS[i], &read_fds);
        }
    }

    //注冊監聽事件
    ret = select(maxsock+1, &read_fds, NULL, NULL, NULL);
    if (ret<0) {
        printf("select error\n");
        continue;
    }else if (ret==0){
        printf("select timeout\n");
        continue;
    }

    //讀取客戶端發來的數據
    for (int i =0; i<user_count; i++) {
        if (FD_ISSET(USERS[i], &read_fds)) {
            ret = recv(USERS[i], buf, sizeof(buf), 0);
            printf("client[%d] send:%s\n", i, buf);
        }
    }

    //處理新用戶鏈接
    if (FD_ISSET(sock_fd, &read_fds)) {
        printf("new client\n");
        int new_fd = accept(sock_fd, (struct sockaddr *)&client_addr, &client_addrlength);
        if (new_fd<0) {
            printf("accept error\n");
            close(new_fd);
            continue;
        }

        USERS[user_count] = new_fd;
        printf("new connection client[%d] %s:%d\n", user_count,
               inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
        user_count++;
        if (new_fd > maxsock){
            maxsock = new_fd;
        }
    }

    showclient();
}




close(sock_fd);
return 0;

}</pre>