https://blog.csdn.net/y396397735/article/details/50680359

本例實現如下功能：?

支持多客戶端與一個服務端進行通信，客戶端給服務端發送字符串數據，服務端將字符串中小寫轉為大寫后發送回客戶端，客戶端打印輸出經轉換后的字符串。?
例如：發送 abcde，打印輸出 ABCDE?
服務端源碼如下：

/*server.c*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <errno.h>#define BUFSIZE 666
#define SERV_PORT 8000
#define OPEN_MAX 1024int main()
{int i, j, maxi, listenfd, connfd, sockfd;int nready, efd, res;ssize_t n;char buf[BUFSIZE], str[INET_ADDRSTRLEN];socklen_t clilen;int client[OPEN_MAX];struct sockaddr_in cliaddr, servaddr;struct epoll_event tep, ep[OPEN_MAX];//監聽事件/*分配一個網絡通信套接字，監聽文件描述符listenfd*/listenfd = socket(AF_INET, SOCK_STREAM, 0);/*初始化 IP類型 端口*/bzero(&servaddr, sizeof(servaddr));servaddr.sin_family = AF_INET;servaddr.sin_addr.s_addr = htonl(INADDR_ANY);servaddr.sin_port = htons(SERV_PORT);/*將listenfd綁定服務端地址*/bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr));/*監聽請求*/listen(listenfd, 20);/*將客戶端標識初始化為-1*/for(i = 0; i < OPEN_MAX; i++){client[i] = -1;}maxi = -1;/*告訴內核要監聽的文件描述符個數 OPEN_MAX = 1024*/efd = epoll_create(OPEN_MAX);if(efd == -1){perror("epoll_create");}tep.events = EPOLLIN;/*監聽文件描述符的可讀事件*/tep.data.fd = listenfd;/*設置為監聽的文件描述符*//*控制epoll監控的文件描述符上的事件*/res = epoll_ctl(efd, EPOLL_CTL_ADD/*注冊新的fd到efd*/, listenfd, &tep);if(res == -1)perror("epoll_ctl");for(;;){/*等待所監控文件描述符上有事件的產生，阻塞監聽*/nready = epoll_wait(efd, ep, OPEN_MAX, -1);if(nready == -1)perror("epoll_wait");for(i = 0; i < nready; i++){if(!(ep[i].events & EPOLLIN))/*若不是EPOLLIN事件，不做往下的處理*/continue;if(ep[i].data.fd == listenfd){ /*若是EPOLLIN，執行連接，接受請求*/clilen = sizeof(cliaddr);/*接受請求，分配新文件描述符connfd進行通信*/connfd = accept(listenfd, (struct sockaddr*)&cliaddr, &clilen);printf("received from %s at PORT %d\n", (char*)inet_ntop(AF_INET, &cliaddr.sin_addr, str, sizeof(str)), ntohs(cliaddr.sin_port));/*若將此新客戶端添加至客戶端集中*/for(j = 0; j < OPEN_MAX; j++)if(client[j] < 0){client[j] = connfd;break;}if(j == OPEN_MAX)perror("客戶端超過限制");if(j > maxi)maxi = j;//保證maxi為最大文件描述符tep.events = EPOLLIN;tep.data.fd = connfd;res = epoll_ctl(efd, EPOLL_CTL_ADD/*注冊新的connfd到efd*/, connfd, &tep);if(res == -1)perror("epoll_ctl");}else{/*處理efd中監聽的客戶端請求*/sockfd = ep[i].data.fd;n = read(sockfd, buf, BUFSIZE);if(n == 0){ /*讀取若為空*/for(j = 0; j <= maxi; j++){if(client[j] == sockfd){client[j] = -1;break;}}/*清除對sockfd文件描述符事件的監聽*/res = epoll_ctl(efd, EPOLL_CTL_DEL, sockfd, NULL);if(res == -1)perror("epoll_ctl");close(sockfd);printf("client[%d] closed connection\n", j);}else{/*非空則處理客戶端信息*/for(j = 0; j<n; j++)buf[j] = toupper(buf[j]);/*寫入與客戶端通信的文件描述符sockfd*/write(sockfd, buf, n);}}}}/*關閉監聽*/close(listenfd);close(efd);return 0;
}

客戶端源碼如下：

/*client.c*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <errno.h>#define BUFSIZE 666
#define SERV_PORT 8000
#define OPEN_MAX 1024int main(int argc, char *argv[])
{struct sockaddr_in servaddr;char buf[BUFSIZE];int sockfd, n;sockfd = socket(AF_INET, SOCK_STREAM, 0);bzero(&servaddr, sizeof(servaddr));servaddr.sin_family = AF_INET;inet_pton(AF_INET, "127.0.0.1", &servaddr.sin_addr);servaddr.sin_port = htons(SERV_PORT);/*連接服務端*/connect(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr));while(fgets(buf, BUFSIZE, stdin) != NULL){/*通過sockfd給服務端發送數據*/write(sockfd, buf, strlen(buf));n = read(sockfd, buf, BUFSIZE);if(n == 0)printf("the other side has been closed.\n");else/*打印輸出服務端傳過來的數據*/write(STDOUT_FILENO, buf, n);}close(sockfd);return 0;
}

---

編譯及執行

在終端1先執行：

yu@ubuntu:~/Linux/217/epoll$ ls
client.c  server.c
yu@ubuntu:~/Linux/217/epoll$ gcc -o client client.c
yu@ubuntu:~/Linux/217/epoll$ gcc -o server server.c
yu@ubuntu:~/Linux/217/epoll$ ./server

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另開一終端2：

yu@ubuntu:~/Linux/217/epoll$ ./client
hey how are you
HEY HOW ARE YOU
bye
BYE

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再另開一終端3：

yu@ubuntu:~/Linux/217/epoll$ ./client
i am here 007
I AM HERE 007
hehe
HEHE

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最后開一終端4：

yu@ubuntu:~/Linux/217/epoll$ ./client
i am 008
I AM 008
zai jian
ZAI JIAN

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關閉3個客戶端(CTR+C)后服務端窗口：

yu@ubuntu:~/Linux/217/epoll$ ./server
received from 127.0.0.1 at PORT 58385
received from 127.0.0.1 at PORT 58386
received from 127.0.0.1 at PORT 58387
client[2] closed connection
client[1] closed connection
client[0] closed connection

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