用select实现服务器并发：

linux@linux:~/study/1001$ cat server.c 
#include <myhead.h>#define ERR_MSG(msg) do{\printf("%d\n",__LINE__);\perror(msg);\
}while(0)#define PORT 8880#define IP "192.168.31.38"int main(int argc, const char *argv[])
{//创建流式套接字 socketint sfd = socket(AF_INET,SOCK_STREAM,0);if(sfd == -1){ERR_MSG("socket");return -1;}printf("socket create success! sfd = %d\n",sfd);//允许端口快速的被复用int reuse = 1;                                                            if(setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse)) < 0){ERR_MSG("setsockopt");return -1;}printf("允许端口快速的被复用成功\n");//绑定服务器的地址信息 --->必须绑定 bindstruct sockaddr_in sin;sin.sin_family = AF_INET;sin.sin_port = htons(PORT);sin.sin_addr.s_addr = inet_addr(IP);if(bind(sfd,(struct sockaddr*)&sin,sizeof(sin)) == -1){ERR_MSG("bind");return -1;}printf("bind success!\n");//将套接字设置为被动监听状态 listenif(listen(sfd,128) == -1){ERR_MSG("listen");return -1;}printf("listen success!\n");fd_set readfds,tempfds;//清空集合FD_ZERO(&readfds);//添加文件描述符FD_SET(0,&readfds);FD_SET(sfd,&readfds);struct sockaddr_in cin;socklen_t addrlen = sizeof(cin);int newfd = -1;char buf[32];ssize_t res = 0;int s_res = -1;int maxfd = sfd;int sndfd = -1;struct sockaddr_in save[1024];while(1){tempfds = readfds;maxfd = maxfd>newfd?maxfd:newfd;s_res = select(maxfd+1,&tempfds,NULL,NULL,NULL);if(s_res == -1){ERR_MSG("select");return -1;}else if(s_res == 0){printf("time out\n");break;}for(int i = 0;i <= maxfd;i++){if(FD_ISSET(i,&tempfds) == 0)continue;if(0 == i){printf("触发键盘输入事件\n");bzero(buf,sizeof(buf));int ret = scanf("%d %s",&sndfd,buf);if(ret != 2){printf("您的输入格式有误：sndfd buf\n");return -1;}if(sndfd <= 2 || FD_ISSET(sndfd,&readfds) == 0){printf("您输入的文件描述符不合法 snfd = %d\n",sndfd);return -1;}//发送if(send(sndfd,buf,sizeof(buf),0) == -1){ERR_MSG("send");return -1;}printf("send success!\n");}else if(sfd == i){printf("触发客户端连接事件\n");//获取一个已经完成的客户端信息，生成一个新的文件描述符 acceptnewfd = accept(sfd,(struct sockaddr*)&cin,&addrlen); if(newfd == -1){ERR_MSG("accept");return -1;}printf("[%s:%d]客户端链接成功! newfd = %d\n",inet_ntoa(cin.sin_addr),ntohs(cin.sin_port),newfd);save[newfd] = cin;FD_SET(newfd,&readfds);}else{printf("触发接收客户端数据事件\n");//接收bzero(buf,sizeof(buf));res = recv(i,buf,sizeof(buf),0);if(res == -1){ERR_MSG("recv");return -1;}else if(res == 0){printf("[%s:%d]客户端已下线! newfd = %d\n",inet_ntoa(save[i].sin_addr),ntohs(save[i].sin_port),i);close(i);FD_CLR(i,&readfds);while(FD_ISSET(maxfd,&readfds) == 0 && maxfd-->=0);continue;}printf("[%s:%d] newfd = %d buf = %s \n",inet_ntoa(save[i].sin_addr),ntohs(save[i].sin_port),i,buf);//发送if(send(i,buf,sizeof(buf),0) == -1){ERR_MSG("send");return -1;}printf("send success!\n");}}}//关闭文件描述符if(close(sfd)<0){ERR_MSG("close");return -1;}if(close(newfd) < 0){ERR_MSG("close");return -1;}return 0;
}

运行结果：