介绍：运行在ubuntu linux系统，需要先打开一个终端运行服务端代码，这时，可以打开多个终端同时运行多个客户端代码（注意客户端数目要小于MAX_FD）;在客户端输入数据后回车，可以看见服务器收到数据，并回复客户端确认信息，客户端输入：exit，按回车，该客户端关闭，在服务器端显示退出信息;所有客户端关闭后，服务器不会自动关闭，需要按ctrl+c强制关闭。
服务器端代码：
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/select.h>
#define SERV_PORT 8888
#define SERV_IP "127.0.0.1" //本地回环接口
#define LIST 20 //服务器最大接受连接
#define MAX_FD 10 //FD_SET支持描述符数量
int main(void)
{
int sockfd;
int err;
int i;
int connfd;
int fd_all[MAX_FD]; //保存所有描述符，用于select调用后，判断哪个可读
//下面两个备份原因是select调用后，会发生变化，再次调用select前，需要重新赋值
fd_set fd_read; //FD_SET数据备份
fd_set fd_select; //用于select
struct timeval timeout; //超时时间备份
struct timeval timeout_select; //用于select
struct sockaddr_in serv_addr; //服务器地址
struct sockaddr_in cli_addr; //客户端地址
socklen_t serv_len;
socklen_t cli_len;
//超时时间设置
timeout.tv_sec = 10;
timeout.tv_usec = 0;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if(sockfd < 0)
{
perror("fail to socket");
exit(1);
}
memset(&serv_addr, 0, sizeof(serv_addr));
memset(&cli_addr, 0, sizeof(cli_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(SERV_PORT);
serv_addr.sin_addr.s_addr = inet_addr(SERV_IP);
serv_len = sizeof(serv_addr);
err = bind(sockfd, (struct sockaddr *)&serv_addr, serv_len);
if(err < 0)
{
perror("fail to bind");
exit(1);
}
err = listen(sockfd, LIST);
if(err < 0)
{
perror("fail to listen");
exit(1);
}
//初始化fd_all数组
memset(&fd_all, -1, sizeof(fd_all));
fd_all[0] = sockfd; //第一个为监听套接字
FD_ZERO(&fd_read);
FD_SET(sockfd, &fd_read); //将监听套接字加入fd_set
char buf[1024]; //读写缓冲区
int num;
int maxfd;
maxfd = fd_all[0]; //监听的最大套接字
while(1)
{
//每次都需要重新赋值
fd_select = fd_read;
timeout_select = timeout;
// err = select(maxfd+1, &fd_select, NULL, NULL, NULL);
err = select(maxfd+1, &fd_select, NULL, NULL, (struct timeval *)&timeout_select);
if(err < 0)
{
perror("fail to select");
exit(1);
}
if(err == 0)
printf("timeout\n");
//检测监听套接字是否可读
if(FD_ISSET(sockfd, &fd_select))
{
//可读，证明有新客户端连接服务器
cli_len = sizeof(cli_addr);
connfd = accept(sockfd, (struct sockaddr *)&cli_addr, &cli_len);
if(connfd < 0)
{
perror("fail to accept");
exit(1);
}
//将新连接套接字加入fd_all及fd_read
for(i=0; i<MAX_FD; i++)
{
if(fd_all[i] != -1)
{
continue;
}
else
{
fd_all[i] = connfd;
printf("client fd_all[%d] join\n", i);
break;
}
}
FD_SET(connfd, &fd_read);
if(maxfd < connfd)
{
maxfd = connfd; //更新maxfd
}
}
//从1开始查看连接套接字是否可读，因为上面已经处理过0（sockfd）
for(i=1; i<maxfd; i++)
{
if(FD_ISSET(fd_all[i], &fd_select))
{
printf("fd_all[%d] is ok\n", i);
num = read(fd_all[i], buf, 1024);
if(num > 0)
{
if(strncmp("exit", buf, 4) == 0)
{
//客户端退出，关闭套接字，并从监听集合清除
printf("client:fd_all[%d] exit\n", i);
FD_CLR(fd_all[i], &fd_read);
close(fd_all[i]);
fd_all[i] = -1;
continue;
}
//收到 客户端数据并打印
buf[num] = '\0';
printf("receive buf from client fd_all[%d] is: %s\n", i, buf);
}
//回复客户端
num = write(fd_all[i], "ok", sizeof("ok"));
if(num < 0)
{
perror("fail to write ");
exit(1);
}
else
{
printf("send reply\n");
}
}
else
{
//printf("no data\n");
}
}
}
return 0;
}
客户端代码：
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define SERV_PORT 8888
#define SERV_IP "127.0.0.1"
int main(void)
{
int sockfd;
int err;
int connfd;
struct sockaddr_in serv_addr;
struct sockaddr_in cli_addr;
socklen_t serv_len;
socklen_t cli_len;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if(sockfd < 0)
{
perror("fail to socket");
exit(1);
}
memset(&serv_addr, 0, sizeof(serv_addr));
memset(&cli_addr, 0, sizeof(cli_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(SERV_PORT);
serv_addr.sin_addr.s_addr = inet_addr(SERV_IP);
serv_len = sizeof(serv_addr);
//客户端不需要绑定，直接连接即可
err = connect(sockfd, (struct sockaddr *)&serv_addr, serv_len);
if(err < 0)
{
perror("fail to bind");
exit(1);
}
char buf[1024];
int num;
while(1)
{
sleep(2);
num = read(STDIN_FILENO, buf, 1024);
if(num > 0)
{
//exit代表退出
if(strncmp("exit", buf, 4) == 0)
{
write(sockfd, buf, num);
break;
}
}
write(sockfd, buf, num);
}
num = read(sockfd, buf, 1024);
if(num > 0)
{
buf[num] = '\0';
printf("server reply: %s\n", buf);
}
else
printf("error to read\n");
}
close(sockfd);
return 0;
}