C语言的UDP广播实现

以下是一个使用epoll和getopt的UDP广播客户端示例。这个客户端会向指定的广播地址发送一条消息，并等待服务器返回的数据包。

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

#define BUF_SIZE 1024
#define EPOLL_EVENTS_NUM 10

int main(int argc, char *argv[]) {
    int port = 0;
    char *broadcast_ip = NULL;
    int opt;

    while ((opt = getopt(argc, argv, "p:b:")) != -1) {
        switch (opt) {
            case 'p':
                port = atoi(optarg);
                break;
            case 'b':
                broadcast_ip = optarg;
                break;
            default:
                fprintf(stderr, "Usage: %s [-p port] [-b broadcast_ip]\n", argv[0]);
                exit(1);
        }
    }

    if (port == 0 || broadcast_ip == NULL) {
        fprintf(stderr, "Please specify both port and broadcast_ip with -p and -b options\n");
        exit(1);
    }

    int sockfd;
    struct sockaddr_in server_addr;

    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) {
        perror("socket");
        exit(1);
    }

    int broadcast_enable = 1;
    if (setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, &broadcast_enable, sizeof(broadcast_enable)) < 0) {
        perror("setsockopt");
        exit(1);
    }

    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(port);
    if (inet_pton(AF_INET, broadcast_ip, &server_addr.sin_addr) <= 0) {
        perror("inet_pton");
        exit(1);
    }

    int epollfd = epoll_create1(0);
    if (epollfd < 0) {
        perror("epoll_create1");
        exit(1);
    }

    struct epoll_event event;
    event.events = EPOLLIN;
    event.data.fd = sockfd;

    if (epoll_ctl(epollfd, EPOLL_CTL_ADD, sockfd, &event) < 0) {
        perror("epoll_ctl");
        exit(1);
    }

    struct epoll_event events[EPOLL_EVENTS_NUM];
    char buffer[BUF_SIZE];

    printf("Please enter the message to send: ");
    fgets(buffer, BUF_SIZE, stdin);
    size_t len = strlen(buffer);
    if (buffer[len - 1] == '\n') {
        buffer[len - 1] = '\0';
    }

    ssize_t send_count = sendto(sockfd, buffer, len, 0, (struct sockaddr *)&server_addr, sizeof(server_addr));
    if (send_count < 0) {
        perror("sendto");
        exit(1);
    }

    while (1) {
        int n = epoll_wait(epollfd, events, EPOLL_EVENTS_NUM, -1);
        for (int i = 0; i < n; i++) {
            if (events[i].events & EPOLLERR || events[i].events & EPOLLHUP || !(events[i].events & EPOLLIN)) {
                fprintf(stderr, "epoll error\n");
                close(events[i].data.fd);
                continue;
            }

            ssize_t count = recvfrom(sockfd, buffer, BUF_SIZE, 0, NULL, NULL);
            if (count < 0) {
                perror("recvfrom");
                exit(1);
            }

            printf("Received message from server: %s\n", buffer);
            break;
        }
    }

    close(sockfd);
    close(epollfd);

    return 0;
}

要编译这个程序，请使用以下命令：

gcc -o udp_broadcast_client udp_broadcast_client.c

然后运行它，指定要发送的广播地址和端口：

./udp_broadcast_client -p <port> -b <broadcast_ip>

这个客户端会向指定的广播地址发送一条消息，然后等待服务器返回的数据包。如果收到服务器返回的数据包，它会将数据包内容打印到屏幕上。