epoll 实现client

下面是使用 epoll 实现的一个简单的 TCP 客户端：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <errno.h>

#define MAX_EVENTS 10
#define BUF_SIZE 1024

int main(int argc, char *argv[]) {
    if (argc != 3) {
        printf("Usage: %s <ip> <port>\n", argv[0]);
        exit(1);
    }

    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd == -1) {
        perror("socket");
        exit(1);
    }

    struct sockaddr_in server_addr;
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = inet_addr(argv[1]);
    server_addr.sin_port = htons(atoi(argv[2]));

    if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
        perror("connect");
        exit(1);
    }

    int epollfd = epoll_create(MAX_EVENTS);
    if (epollfd == -1) {
        perror("epoll_create");
        exit(1);
    }

    struct epoll_event ev, events[MAX_EVENTS];
    memset(&ev, 0, sizeof(ev));
    ev.events = EPOLLIN;
    ev.data.fd = sockfd;

    if (epoll_ctl(epollfd, EPOLL_CTL_ADD, sockfd, &ev) == -1) {
        perror("epoll_ctl");
        exit(1);
    }

    char buf[BUF_SIZE];
    while (1) {
        int nfds = epoll_wait(epollfd, events, MAX_EVENTS, -1);
        if (nfds == -1) {
            if (errno == EINTR) {
                continue;
            }
            perror("epoll_wait");
            exit(1);
        }

        for (int i = 0; i < nfds; ++i) {
            if (events[i].data.fd == sockfd) {
                int n = read(sockfd, buf, BUF_SIZE);
                if (n == -1) {
                    perror("read");
                    exit(1);
                } else if (n == 0) {
                    printf("Server closed connection\n");
                    close(sockfd);
                    exit(0);
                } else {
                    buf[n] = '\0';
                    printf("Received message: %s", buf);
                }
            }
        }
    }

    return 0;
}

首先创建了一个 socket，并连接到指定的服务器。然后创建一个 epoll 实例，将 socket 加入到 epoll 中，并设置监听的事件类型为可读。之后不断循环调用 epoll_wait 等待事件的发生，如果是 socket 的可读事件，则读取数据并打印。