写一个c语言组播收发数据的例子

在C语言中，由于原生标准库并不直接支持组播功能，我们通常需要借助于网络编程库，如socket API或者更高级的libevent、libuv等。下面是一个简单的UDP（User Datagram Protocol）组播收发数据的例子，它使用了socket编程：

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

#define MAX_PACKET_SIZE 1024

void send_group_message(char *message, char *group_ip, int port) {
    struct sockaddr_in server;
    socklen_t addrlen = sizeof(server);
    int sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

    if (sock == -1) {
        perror("Error creating socket");
        exit(1);
    }

    server.sin_family = AF_INET;
    inet_pton(AF_INET, group_ip, &server.sin_addr);
    server.sin_port = htons(port);

    if (setsockopt(sock, IPPROTO_IP, IP_MULTICAST_TTL, (char *)&ttl, sizeof(ttl)) == -1) {
        perror("Error setting multicast TTL");
    }
    
    if (sendto(sock, message, strlen(message), 0, (struct sockaddr *)&server, addrlen) == -1) {
        perror("Error sending data to group");
    }

    close(sock);
}

void receive_group_message(char *buffer, size_t bufsize, char *group_ip, int port) {
    struct sockaddr_in source;
    socklen_t len = sizeof(source);
    int sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&reuseaddr, sizeof(reuseaddr));

    if (bind(sock, (struct sockaddr *)&source, len) == -1) {
        perror("Error binding to receive port");
    }

    if (setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (void *)&mreq, sizeof(mreq)) == -1) {
        perror("Error joining multicast group");
    }

    while (true) {
        ssize_t bytes_received = recvfrom(sock, buffer, bufsize, 0, (struct sockaddr *)&source, &len);
        if (bytes_received > 0) {
            printf("Received message from %s:%d: %s\n", inet_ntoa(source.sin_addr), ntohs(source.sin_port), buffer);
        } else {
            perror("Error receiving data");
            break;
        }
    }

    close(sock);
}

int main() {
    char message[] = "Hello, Group!";
    char group_ip[] = "224.0.0.1"; // 组播IP地址，如"224.0.0.1"
    int port = 5000; // 发送端和接收端相同的端口
    int ttl = 1; // 设置TTL（Time To Live），用于限制消息传播范围
    bool reuseaddr = 1; // 设置SO_REUSEADDR标志
    struct ip_mreq mreq;
    mreq.imr_multiaddr.s_addr = inet_addr(group_ip);
    mreq.imr_interface.s_addr = htonl(INADDR_ANY);

    send_group_message(message, group_ip, port);
    receive_group_message(buffer, MAX_PACKET_SIZE, group_ip, port);

    return 0;
}

注意：这个例子假设你已经在系统上配置了组播功能，并且运行程序的主机连接到同一子网内的组播路由器。同时，为了能够成功发送和接收，接收端也需要加入相应的组播组。