selectServerInTCPIPbook.c的内容如下：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/select.h>

#define BUF_SIZE 100
void error_handling(char *buf);

int main(int argc, char *argv[])
{
	int serv_sock, clnt_sock;
	struct sockaddr_in serv_adr, clnt_adr;
	struct timeval timeout;
	fd_set reads, cpy_reads;

	socklen_t adr_sz;
	int fd_max, str_len, fd_num, i;
	char buf[BUF_SIZE];
	if(argc!=2) {
		printf("Usage : %s <port>\n", argv[0]);
		exit(1);
	}

	serv_sock=socket(PF_INET, SOCK_STREAM, 0);
	memset(&serv_adr, 0, sizeof(serv_adr));
	serv_adr.sin_family=AF_INET;
	serv_adr.sin_addr.s_addr=htonl(INADDR_ANY);
	serv_adr.sin_port=htons(atoi(argv[1]));
	
	if(bind(serv_sock, (struct sockaddr*) &serv_adr, sizeof(serv_adr))==-1)
		error_handling("bind() error");
	if(listen(serv_sock, 5)==-1)
		error_handling("listen() error");

	FD_ZERO(&reads);
	FD_SET(serv_sock, &reads);
	FD_SET(0, &reads);
	fd_max=serv_sock;
	char send_line[BUF_SIZE];

	while(1)
	{
		cpy_reads=reads;
		timeout.tv_sec=5;
		timeout.tv_usec=5000;

		if((fd_num=select(fd_max+1, &cpy_reads, 0, 0, &timeout))==-1)
			break;
		
		if(fd_num==0)
			continue;



		if (FD_ISSET(STDIN_FILENO, &cpy_reads)) {
            FD_CLR(0, &cpy_reads);
            if (fgets(send_line, BUF_SIZE, stdin) != NULL) {
                int i = strlen(send_line);
                if (send_line[i - 1] == '\n') {
                    send_line[i - 1] = 0;
                }
                printf("input: %s\n", send_line);
            }
        }

		for(i=1; i<fd_max+1; i++)
		{
			if(FD_ISSET(i, &cpy_reads))
			{
				if(i==serv_sock)  
				{
					adr_sz=sizeof(clnt_adr);
					clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_adr, &adr_sz);
					FD_SET(clnt_sock, &reads);
					if(fd_max<clnt_sock)
						fd_max=clnt_sock;
					printf("connected client: %d \n", clnt_sock);
				}
				else
				{
					str_len=read(i, buf, BUF_SIZE);
					if(str_len==0)
					{
						FD_CLR(i, &reads);
						close(i);
						printf("closed client: %d \n", i);
					}
					else
					{
						write(1, "message from clien:", 19);
						write(1, buf, str_len);					   
						write(1,"\n",1);
						write(i, "message from server:", 20);
						write(i, buf, str_len);  
					}
				}
			}
		}
	}
	close(serv_sock);
	return 0;
}

void error_handling(char *buf)
{
	fputs(buf, stderr);
	fputc('\n', stderr);
	exit(1);
}

gcc selectServerInTCPIPbook.c -o selectServerInTCPIPbook进行编译，然后./selectServerInTCPIPbook 8080端口上监听。

selectClient.c里边的内容：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<arpa/inet.h>
#include<sys/socket.h>
#define  MAXLINE     1024
int main(int argc, char **argv) {
    if (argc != 3) {
        printf("usage: select01 <IPaddress> or <Port>");
    }



    int socket_fd = socket(AF_INET,SOCK_STREAM,0);

    struct sockaddr_in server_addr;
    bzero(&server_addr,sizeof(server_addr));

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(atoi(argv[2]));
    inet_pton(AF_INET,argv[1],&server_addr.sin_addr);

    socklen_t server_len = sizeof(server_addr);
    int connect_rt = connect(socket_fd,(struct sockaddr *)&server_addr,server_len);
    if(connect_rt<0){
        printf("connect failed");
        exit(0);
    }

    char recv_line[MAXLINE], send_line[MAXLINE];
    int n;

    fd_set readmask;
    fd_set allreads;
    FD_ZERO(&allreads);
    FD_SET(0, &allreads);
    FD_SET(socket_fd, &allreads);
    
    for (;;) {
        readmask = allreads;
        int rc = select(socket_fd + 1, &readmask, NULL, NULL, NULL);

        if (rc <= 0) {
           printf("select failed\n");
           exit(0);
        }

        if (FD_ISSET(socket_fd, &readmask)) {
            n = read(socket_fd, recv_line, MAXLINE);
            if (n < 0) {
                printf("read error\n");
                exit(0);
            } else if (n == 0) {
               printf("server terminated\n");
               exit(0);
            }
            recv_line[n] = 0;
            fputs(recv_line, stdout);
            fputs("\n", stdout);
        }

        if (FD_ISSET(STDIN_FILENO, &readmask)) {
            // FD_CLR(0, &allreads); //去掉注册到操作系统里边标准输出的内容
            if (fgets(send_line, MAXLINE, stdin) != NULL) {
                int i = strlen(send_line);
                if (send_line[i - 1] == '\n') {
                    send_line[i - 1] = 0;
                }

                printf("now sending %s\n", send_line);
                size_t rt = write(socket_fd, send_line, strlen(send_line));
                if (rt < 0) {
                    printf("write failed\n");
                    exit(0);
                }
                printf("send bytes: %zu \n", rt);
            }
        }
    }

}

再打开一个终端，gcc selectClient.c -o selectClient进行编译，然后使用./selectClient 127.0.0.1 8080连接到自己本机上8080端口。
之后再客户端上输入good之后，可以看到客户端收到的message from server:good这条信息，而服务器也收到了good的字符串。

为了验证服务器的select多路复用，使用键盘在服务器这里输入test字符串，可以看到服务器输出了input: test而客户端没有任何输出。

此文章为11月Day 13学习笔记，内容来源于极客时间《网络编程实战》。