// servfd监听描述符，acceptfd连接描述符

int servfd, acceptfd;

struct sockaddr_in my_addr;

// 创建套接字（IPv4 + TCP）

if((servfd == socket(AF_INET, SOCK_STREAM, 0) == -1)) {

perror("socket");

return -1;

}

printf("socket ok \n");

// 设置sockaddr_in结构的类型，端口号，IP地址

my_addr.sin_family = AF_INET;

my_addr.sin_port = htons(6666);

my_addr.sin_addr.s_addr = htonl(INADDR_ANY);

// 对my_addr清零

bzero(&(my_addr.sin_zero), 0);

// 将套接字描述符和sockaddr_in结构绑定

if(bind(servfd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr)) == -1){

perror("bind");

return -2;

}

printf("bind ok\n");

int maxsock = servfd;

fd_set client_fdset;

struct timeval tv;

int client_sockfd[5];

bzero((void *)client_sockfd, sizeof(client_sockfd));

int conn_amount = 0;

char buffer[1024];

int ret = 0;

while(1){

// 将fd_set集合置零并重设fd位，设置超时时间

FD_ZERO(&client_fdset);

FD_SET(servfd, &client_fdset);

tv.tv_sec = 30;

tv.tv_usec = 0;

// 把已连上的client描述符加入集合中

for(int i = 0; i < 5; ++i){

if(client_sockfd[i] != 0)

FD_SET(client_sockfd[i], &client_fdset);

}

// 调用select函数并检查是否正确

ret = select(maxsock + 1, &client_fdset, NULL, NULL, &tv);

if(ret < 0){

perror("select error \n");

break;

}

else if(ret == 0){

printf("timeout \n");

continue;

}

// 遍历每一个已连上的client的fd，查看是否有数据，conn_amount初始为0

for(int i = 0; i < conn_amount; ++i) {

if(FD_ISSET(client_sockfd[i], &client_fdset)){

printf("start recv from client[%d] : \n", i);

ret = recv(client_sockfd[i], buffer, 1024, 0);

// 无数据可读则关闭连接且在集合中清理掉

if(ret <= 0){

printf("client[%d] close\n", i);

close(client_sockfd[i]);

FD_CLR(client_sockfd[i], &client_fdset);

client_sockfd[i] = 0;

}

// 有数据可读

else

printf("recv from client[%d] : %s\n", i, buffer);

}

}

// 检查是否有新连接

if(FD_ISSET(servfd, &client_fdset)){

struct sockaddr_in client_addr;

size_t size = sizeof(struct sockaddr_in);

// 服务器接收新连接并返回连接描述符sock_client

int sock_client = accept(servfd, (struct sockaddr *)(&client_addr), (unsigned int *)(&size));

if(sock_client < 0){

perror("accept error \n");

continue;

}

// 已连接数小于5接受新连接

if(conn_amount < 5){

client_sockfd[conn_amount++] = sock_client;

bzero(buffer, 1024);

// 建立起连接向客户机发送消息

strcpy(buffer, "this is server ! welcome \n ");

send(sock_client, buffer, 1024, 0);

// 打印客户机信息，IP + port

printf("new connection client[%d] %s : %d \n", conn_amount, inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));

bzero(buffer, sizeof(buffer));

// 开始调用recv接收用户输入数据

ret = recv(sock_client, buffer, 1024, 0);

if(ret < 0){

perror("recv error \n");

close(servfd);

return -1;

}

printf("recv : %s \n", buffer);

// 检查新建立连接的描述符是否比当前最大的更大并更新（select第一个参数）

if(sock_client > maxsock) {

maxsock = sock_client;

}

}

// 超过最大连接

else{

printf("max connections, quit \n");

break;

}

}

}

// 关掉已连上的fd和自身fd

for(int i = 0; i < 5; ++i){

if(client_sockfd[i] != 0)

close(client_sockfd[i]);

}

close(servfd);

return 0;