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文章提供了两个示例，分别是使用select实现的TCP并发服务器和客户端，以及使用poll实现的TCP并发客户端。服务器通过select进行多路复用，监听客户端连接并处理交互事件。客户端利用poll监控标准输入和服务器连接，实现数据收发。

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TCP 并发服务器 select实现

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>
#include <sys/select.h>

#define ERR_MSG(msg) do{\
	fprintf(stderr,"line=__%d__",__LINE__);\
	perror(msg);\
}while(0)

//服务器地址＋端口
#define SER_PORT 2222 //1024~49151
#define SER_IP "192.168.31.200" 

int main(int argc, const char *argv[])
{ 
	//创建一个新的套接字
	int sfd = socket(AF_INET,SOCK_STREAM,0);
	if(-1 == sfd){
		ERR_MSG("socket");
		return -1;
	}
	printf("sfd=%d\n",sfd);
	
	//设置套接字选项
	int reuse = 1;
	if(setsockopt(sfd,SOL_SOCKET,SO_REUSEADDR,&reuse,sizeof(reuse)) < 0){
		ERR_MSG("setsockopt");
		return -1;
	}
	printf("setsockopt success\n");
	
	//地址信息结构体
	struct sockaddr_in sin;
	//IPV4 地址簇
	sin.sin_family = AF_INET;
	//将端口号从主机字节序转成网络字节序
	sin.sin_port = htons(SER_PORT);
	//将IPV4地址的字符串转换为网络字节序的整数
	sin.sin_addr.s_addr = inet_addr(SER_IP);

	//将IP地址和端口号绑定到指定套接字中
	if(bind(sfd,(struct sockaddr*)&sin,sizeof(sin)) < 0){
		ERR_MSG("bind");
		return -1;
	}
	printf("bind success\n");
	
	//将套接字设置为被动监听状态，只负责监听是否有客户端连接成功
	if(listen(sfd,10) < 0){
		ERR_MSG("listen");
		return -1;
	}
	printf("listen success\n");

	fd_set readfds,tempfds;
	int maxfd = sfd;

	FD_ZERO(&readfds);
	FD_ZERO(&tempfds);

	FD_SET(0,&readfds);
	FD_SET(sfd,&readfds);

	int s_res = 0;

	int newfd = -1;
	ssize_t res = 0;
	char buf[128] = "";

	//存储客户端的地址信息
	int dtablesize = getdtablesize();
	struct sockaddr_in clients[dtablesize-4];//0 1 2 sfd
	struct sockaddr_in cin;
	socklen_t addrlen = sizeof(cin);

	while(1){
		tempfds = readfds;
		
		s_res = select(maxfd+1,&tempfds,NULL,NULL,NULL);
		if(s_res < 0){
			ERR_MSG("select");
			return -1;
		}else if(0 == s_res){
			printf("time out\n");
			break;
		}
		
		for(int i=0;i<=maxfd;i++){

			if(FD_ISSET(i,&tempfds) == 0){
				continue;
			}
			
			if(0 == i){
				//键盘触发
				int sndfd;
				res = scanf("%d %s",&sndfd,buf);
				while(getchar() != 10);
				if(res != 2){
					fprintf(stderr,"请输入正确格式:文件描述符　内容\n");
					continue;
				}
				if( sndfd >= dtablesize || sndfd <= sfd || !FD_ISSET(sndfd,&readfds) ){
					fprintf(stderr,"sndfd=%d 没有对应的客户端\n",sndfd);
					continue;
				}
				
				if(send(sndfd,buf,sizeof(buf),0) < 0){
					ERR_MSG("send");
					return -1;
				}
				
				printf("send success\n");
			}else if(sfd == i){
				//触发客户端连接
				newfd = accept(sfd,(struct sockaddr *)&cin,&addrlen);
				if(newfd < 0){
					ERR_MSG("accept");
					return -1;
				}
				printf("newfd=%d\n",newfd);
				printf("[%s:%d]\n",inet_ntoa(cin.sin_addr),ntohs(cin.sin_port));
				
				clients[newfd-4] = cin;

				FD_SET(newfd,&readfds);

				maxfd = maxfd>newfd?maxfd:newfd;
			}else{
				//触发客户端交互事件
				bzero(buf,sizeof(buf));

				//从一个已经连接的socket接收数据
				res = read(i,buf,sizeof(buf));
				if(res < 0){
					//=-1　运行失败
					ERR_MSG("recv");
				}else if(0 == res){
					fprintf(stderr,"[%s:%d] 客户端断开连接\n",\
							inet_ntoa(cin.sin_addr),\
							ntohs(cin.sin_port));
					close(i);
					FD_CLR(i,&readfds);
					for(int j=maxfd;j>sfd;j--){
						if(FD_ISSET(j,&readfds)){
							maxfd = j;
							break;
						}
					}
				}else{
					printf("rcv [%s:%d] newfd=%d buf=%s\n",\
							inet_ntoa(clients[i-4].sin_addr),\
							ntohs(clients[i-4].sin_port),i,buf);	
					//发送---->谁发给我数据，我就发还给谁
					strcat(buf,"*_*");
					//将数据发送给指定的套接字文件描述符中
					if(send(i,buf,sizeof(buf),0) < 0){
						ERR_MSG("send");
						return -1;
					}
					printf("send success\n");
				}
			}
		}
	}
	
	close(sfd);

	return 0;
}

TCP 并发客户端 select实现

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>
#include <sys/select.h>

#define ERR_MSG(msg) do{\
	fprintf(stderr,"line=__%d__",__LINE__);\
	perror(msg);\
}while(0)

//服务器地址＋端口
#define SER_PORT 2222 //1024~49151
#define SER_IP "192.168.31.200" 

int main(int argc, const char *argv[])
{ 
	//创建一个新的套接字
	int sfd = socket(AF_INET,SOCK_STREAM,0);
	if(-1 == sfd){
		ERR_MSG("socket");
		return -1;
	}
	printf("sfd=%d\n",sfd);
	
	//设置套接字选项
	int reuse = 1;
	if(setsockopt(sfd,SOL_SOCKET,SO_REUSEADDR,&reuse,sizeof(reuse)) < 0){
		ERR_MSG("setsockopt");
		return -1;
	}
	printf("setsockopt success\n");
	
	//地址信息结构体
	struct sockaddr_in sin;
	//IPV4 地址簇
	sin.sin_family = AF_INET;
	//将端口号从主机字节序转成网络字节序
	sin.sin_port = htons(SER_PORT);
	//将IPV4地址的字符串转换为网络字节序的整数
	sin.sin_addr.s_addr = inet_addr(SER_IP);

	//将IP地址和端口号绑定到指定套接字中
	if(bind(sfd,(struct sockaddr*)&sin,sizeof(sin)) < 0){
		ERR_MSG("bind");
		return -1;
	}
	printf("bind success\n");
	
	//将套接字设置为被动监听状态，只负责监听是否有客户端连接成功
	if(listen(sfd,10) < 0){
		ERR_MSG("listen");
		return -1;
	}
	printf("listen success\n");

	fd_set readfds,tempfds;
	int maxfd = sfd;

	FD_ZERO(&readfds);
	FD_ZERO(&tempfds);

	FD_SET(0,&readfds);
	FD_SET(sfd,&readfds);

	int s_res = 0;

	int newfd = -1;
	ssize_t res = 0;
	char buf[128] = "";

	//存储客户端的地址信息
	int dtablesize = getdtablesize();
	struct sockaddr_in clients[dtablesize-4];//0 1 2 sfd
	struct sockaddr_in cin;
	socklen_t addrlen = sizeof(cin);

	while(1){
		tempfds = readfds;
		
		s_res = select(maxfd+1,&tempfds,NULL,NULL,NULL);
		if(s_res < 0){
			ERR_MSG("select");
			return -1;
		}else if(0 == s_res){
			printf("time out\n");
			break;
		}
		
		for(int i=0;i<=maxfd;i++){

			if(FD_ISSET(i,&tempfds) == 0){
				continue;
			}
			
			if(0 == i){
				//键盘触发
				int sndfd;
				res = scanf("%d %s",&sndfd,buf);
				while(getchar() != 10);
				if(res != 2){
					fprintf(stderr,"请输入正确格式:文件描述符　内容\n");
					continue;
				}
				if( sndfd >= dtablesize || sndfd <= sfd || !FD_ISSET(sndfd,&readfds) ){
					fprintf(stderr,"sndfd=%d 没有对应的客户端\n",sndfd);
					continue;
				}
				
				if(send(sndfd,buf,sizeof(buf),0) < 0){
					ERR_MSG("send");
					return -1;
				}
				
				printf("send success\n");
			}else if(sfd == i){
				//触发客户端连接
				newfd = accept(sfd,(struct sockaddr *)&cin,&addrlen);
				if(newfd < 0){
					ERR_MSG("accept");
					return -1;
				}
				printf("newfd=%d\n",newfd);
				printf("[%s:%d]\n",inet_ntoa(cin.sin_addr),ntohs(cin.sin_port));
				
				clients[newfd-4] = cin;

				FD_SET(newfd,&readfds);

				maxfd = maxfd>newfd?maxfd:newfd;
			}else{
				//触发客户端交互事件
				bzero(buf,sizeof(buf));

				//从一个已经连接的socket接收数据
				res = read(i,buf,sizeof(buf));
				if(res < 0){
					//=-1　运行失败
					ERR_MSG("recv");
				}else if(0 == res){
					fprintf(stderr,"[%s:%d] 客户端断开连接\n",\
							inet_ntoa(cin.sin_addr),\
							ntohs(cin.sin_port));
					close(i);
					FD_CLR(i,&readfds);
					for(int j=maxfd;j>sfd;j--){
						if(FD_ISSET(j,&readfds)){
							maxfd = j;
							break;
						}
					}
				}else{
					printf("rcv [%s:%d] newfd=%d buf=%s\n",\
							inet_ntoa(clients[i-4].sin_addr),\
							ntohs(clients[i-4].sin_port),i,buf);	
					//发送---->谁发给我数据，我就发还给谁
					strcat(buf,"*_*");
					//将数据发送给指定的套接字文件描述符中
					if(send(i,buf,sizeof(buf),0) < 0){
						ERR_MSG("send");
						return -1;
					}
					printf("send success\n");
				}
			}
		}
	}
	
	close(sfd);

	return 0;
}

TCP 并发客户端 poll实现

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>
#include <poll.h>

#define ERR_MSG(msg) do{\
	fprintf(stderr,"line=__%d__",__LINE__);\
	perror(msg);\
}while(0)

#define SER_PORT 2222 //1024~49151
#define SER_IP "192.168.31.200" 

#define CLI_PORT 4444
#define CLI_IP "192.168.31.200" 

int main(int argc, const char *argv[])
{ 
	//创建套接字
	int cfd = socket(AF_INET,SOCK_STREAM,0);
	if(cfd < 0){
		ERR_MSG("socket");
		return -1;
	}

	//客户端信息结构体
	struct sockaddr_in cin;
	cin.sin_family = AF_INET;
	cin.sin_port = htons(CLI_PORT);
	cin.sin_addr.s_addr = inet_addr(CLI_IP);

	//bind　将ip地址和端口号绑定到指定套接字 非必须绑定
	if(bind(cfd,(struct sockaddr *)&cin,sizeof(cin)) < 0){
		ERR_MSG("bind");
		return -1;
	}
	printf("client bind success\n");

	//服务器端结构体
	struct sockaddr_in sin;
	sin.sin_family = AF_INET;
	sin.sin_port = htons(SER_PORT);
	sin.sin_addr.s_addr = inet_addr(SER_IP);

	//连接服务器
	//int connect(int sockfd, const struct sockaddr *addr,socklen_t addrlen);
	if(connect(cfd,(struct sockaddr *)&sin,sizeof(sin)) < 0){
		ERR_MSG("connect");
		return -1;
	}
	printf("connect server success\n");

	char buf[128];
	ssize_t res = 0;

	struct pollfd fds[2];
	fds[0].fd = 0;
	fds[0].events = POLLIN;

	fds[1].fd = cfd;
	fds[1].events = POLLIN;

	int p_res = 0 ;

	while(1){

		p_res = poll(fds,2,-1);
		if(p_res < 0){
			ERR_MSG("poll");
			return -1;
		}else if(0 == p_res){
			printf("time out\n");
			break;
		}

		if(fds[0].revents&POLLIN){
			bzero(buf,sizeof(buf));
			fgets(buf,sizeof(buf),stdin);
			buf[strlen(buf)-1] = 0;
			//发送信息
			if(send(cfd , buf , sizeof(buf),0) < 0){
				ERR_MSG("send");
				return -1;
			}
			printf("send success\n");
		}
		if(fds[1].revents&POLLIN){
			bzero(buf,sizeof(buf));
			//接收信息
			res = recv(cfd,buf,sizeof(buf),0);
			if(res < 0){
				ERR_MSG("recv");
				return -1;
			}else if( 0 == res){
				printf("sever close!\n");
				break;
			}
			printf("rcv buf = %s\n",buf);
		}

	}


	close(cfd);

	return 0;
}