温馨注意：
1、每次select前最好都要重新设置一下fd_set
2、不要忘记关闭socket
3、将server_sockfd用fcntl设置为非阻塞
4、select最后一个超时参数，0表示不阻塞，-1表示一直阻塞直到事件发送，还有自定义超时时间。
服务器端代码：
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/socket.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include <sys/fcntl.h>
void select_test(int port, int backlog) {
int rcd;
int new_cli_fd;
int maxfd;
int socklen, server_len;
int ci;
int watch_fd_list[backlog + 1];
for (ci = 0; ci <= backlog; ci++)
watch_fd_list[ci] = -1;
int server_sockfd;
//建立socket，类型为TCP流
server_sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (server_sockfd == -1) {
printf("create server_socket error!\n");
exit(1);
}
//设为非阻塞
if (fcntl(server_sockfd, F_SETFL, O_NONBLOCK) == -1) {
printf("Set server socket nonblock failed\n");
exit(1);
}
struct sockaddr_in server_sockaddr;
memset(&server_sockaddr, 0, sizeof(server_sockaddr));
server_sockaddr.sin_family = AF_INET;
server_sockaddr.sin_addr.s_addr = htonl(INADDR_ANY);
//设置监听端口
server_sockaddr.sin_port = htons(port);
server_len = sizeof(server_sockaddr);
//绑定
rcd = bind(server_sockfd, (struct sockaddr *) &server_sockaddr, server_len);
if (rcd == -1) {
printf("bind port %d error!\n", ntohs(server_sockaddr.sin_port));
exit(1);
}
//监听
rcd = listen(server_sockfd, backlog);
if (rcd == -1) {
printf("listen error!\n");
exit(1);
}
printf("Server is waiting on socket=%d \n", server_sockfd);
watch_fd_list[0] = server_sockfd;
maxfd = server_sockfd;
//初始化监听集合
fd_set watchset;
FD_ZERO(&watchset);
FD_SET(server_sockfd, &watchset);
struct timeval tv; /* 声明一个时间变量来保存时间 */
struct sockaddr_in cli_sockaddr;
while (1) {
tv.tv_sec = 20;
tv.tv_usec = 0; /* 设置select等待的最大时间为20秒*/
//每次都要重新设置集合才能激发事件
FD_ZERO(&watchset);
FD_SET(server_sockfd, &watchset);
//对已存在到socket重新设置
for (ci = 0; ci <= backlog; ci++)
if (watch_fd_list[ci] != -1) {
FD_SET(watch_fd_list[ci], &watchset);
}
rcd = select(maxfd + 1, &watchset, NULL, NULL, &tv);
switch (rcd) {
case -1:
printf("Select error\n");
exit(1);
case 0:
printf("Select time_out\n");
//超时则清理掉所有集合元素并关闭所有与客户端的socket
FD_ZERO(&watchset);
for (ci = 1; ci <= backlog; ci++){
shutdown(watch_fd_list[ci],2);
watch_fd_list[ci] = -1;
}
//重新设置监听socket，等待链接
FD_CLR(server_sockfd, &watchset);
FD_SET(server_sockfd, &watchset);
continue;
default:
//检测是否有新连接建立
if (FD_ISSET(server_sockfd, &watchset)) { //new connection
socklen = sizeof(cli_sockaddr);
new_cli_fd = accept(server_sockfd,
(struct sockaddr *) &cli_sockaddr, &socklen);
if (new_cli_fd < 0) {
printf("Accept error\n");
exit(1);
}
printf("\nopen communication with Client %s on socket %d\n",
inet_ntoa(cli_sockaddr.sin_addr), new_cli_fd);
for (ci = 1; ci <= backlog; ci++) {
if (watch_fd_list[ci] == -1) {
watch_fd_list[ci] = new_cli_fd;
break;
}
}
FD_SET(new_cli_fd, &watchset);
if (maxfd < new_cli_fd) {
maxfd = new_cli_fd;
}
continue;
} else {//已有连接的数据通信
//遍历每个设置过的集合元素
for (ci = 1; ci <= backlog; ci++) { //data
if (watch_fd_list[ci] == -1)
continue;
if (!FD_ISSET(watch_fd_list[ci], &watchset)) {
continue;
}
char buffer[128];
//接收
int len = recv(watch_fd_list[ci], buffer, 128, 0);
if (len < 0) {
printf("Recv error\n");
exit(1);
}
buffer[len] = 0;
//获得客户端的IP地址
struct sockaddr_in sockaddr;
getpeername(watch_fd_list[ci], (struct sockaddr*) &sockaddr,
sizeof(sockaddr));
printf("read data [%s] from Client %s on socket %d\n",
buffer,inet_ntoa(sockaddr.sin_addr),watch_fd_list[ci]);
//发送接收到到数据
len = send(watch_fd_list[ci], buffer, strlen(buffer), 0);
if (len < 0) {
printf("Send error\n");
exit(1);
}
printf("write data [%s] to Client %s on socket %d\n",
buffer, inet_ntoa(sockaddr.sin_addr),
watch_fd_list[ci]);
shutdown(watch_fd_list[ci],2);
watch_fd_list[ci] = -1;
FD_CLR(watch_fd_list[ci], &watchset);
//接收到的是关闭命令
if (strcmp(buffer, "quit") == 0) {
for (ci = 0; ci <= backlog; ci++)
if (watch_fd_list[ci] != -1) {
shutdown(watch_fd_list[ci],2);
}
printf("\nWeb Server Quit!\n");
exit(0);
}
}
}
break;
}
}
}
<p>#define backlog 5
const int port = 8888;</p><p>int main() {
select_test(port,backlog);
return 0;
}</p>
客户端代码：
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
int client_tcp(char *serIP,in_port_t serPort,char *data);
int main()
{
int port=8888;
client_tcp("127.0.0.1",port,"Hello Server1!");
client_tcp("127.0.0.1",port,"Hello Server2!");
client_tcp("127.0.0.1",port,"Hello Server3!");
client_tcp("127.0.0.1",port,"quit");
}
int client_tcp(char *serIP,in_port_t serPort,char *data)
{
//创建socket
int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (sock < 0) {
printf("socket Error!");
exit(0);
}
//填充sockaddr_in
struct sockaddr_in serAddr;
memset(&serAddr, 0, sizeof(serAddr));
serAddr.sin_family = AF_INET;
serAddr.sin_port = htons(serPort);
int rtn = inet_pton(AF_INET, serIP, &serAddr.sin_addr.s_addr);
//或者是 serAddr.sin_addr.s_addr=inet_addr(serIP);
if (rtn <= 0) {
printf("inet_pton Error!");
exit(0);
}
printf("目标服务器地址：%s: %d\n", inet_ntoa(serAddr.sin_addr), ntohs(serAddr.sin_port));
printf(" 网络层协议：%s\n", serAddr.sin_family == 2 ? "IPv4" : "IPv6");
printf(" 传输层协议：TCP\n");
//链接服务器
if (connect(sock, (struct sockaddr *) &serAddr, sizeof(serAddr)) < 0) {
printf("connect Error!!\n");
exit(0);
}
//show the other side
printf("connected Server %s : %d\n", inet_ntoa(serAddr.sin_addr), ntohs(serAddr.sin_port));
//发送数据
int bufsize = strlen(data);
int num = send(sock, data, bufsize, 0);
if (num <= 0) {
printf("Send Error!!\n");
exit(0);
}
//接收数据
fputs("Received: ", stdout);
char buffer[100];
int n = recv(sock, buffer, 100 - 1, 0);
if (n <= 0) {
printf("Receive Error!!\n");
exit(0);
} else {
buffer[n] = '\0';
printf("%s\n", buffer);
}
//关闭socket
close(sock);
//exit(0);
return 0;
}
