UDP中的单播，多播，广播（代码实现）

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1. UDP 单播（Unicast）示例

发送方向指定单个目标 IP 地址和端口发送数据，接收方绑定端口接收。

// UDP单播发送示例
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>int main() {int sockfd;struct sockaddr_in dest_addr;char *msg = "Hello UDP Unicast!";sockfd = socket(AF_INET, SOCK_DGRAM, 0);  // 创建UDP套接字if (sockfd < 0) {perror("socket error");return -1;}memset(&dest_addr, 0, sizeof(dest_addr));dest_addr.sin_family = AF_INET;dest_addr.sin_port = htons(12345);  // 目标端口inet_pton(AF_INET, "192.168.1.100", &dest_addr.sin_addr);  // 目标IPsendto(sockfd, msg, strlen(msg), 0, (struct sockaddr*)&dest_addr, sizeof(dest_addr)); // 发送数据printf("UDP Unicast message sent.\n");close(sockfd);return 0;
}

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2. UDP 广播（Broadcast）示例

向同一网段内所有主机发送数据，需要开启套接字广播权限。

// UDP广播发送示例
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>int main() {int sockfd;struct sockaddr_in broadcast_addr;char *msg = "Hello UDP Broadcast!";int broadcastEnable = 1;sockfd = socket(AF_INET, SOCK_DGRAM, 0);if (sockfd < 0) {perror("socket error");return -1;}// 允许广播权限if (setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, &broadcastEnable, sizeof(broadcastEnable)) < 0) {perror("setsockopt error");close(sockfd);return -1;}memset(&broadcast_addr, 0, sizeof(broadcast_addr));broadcast_addr.sin_family = AF_INET;broadcast_addr.sin_port = htons(12345);inet_pton(AF_INET, "192.168.1.255", &broadcast_addr.sin_addr); // 广播地址，一般是子网广播地址sendto(sockfd, msg, strlen(msg), 0, (struct sockaddr*)&broadcast_addr, sizeof(broadcast_addr));printf("UDP Broadcast message sent.\n");close(sockfd);return 0;
}

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3. UDP 多播（Multicast）示例

多播发送时，发送方把数据发到多播地址和端口；接收方需要加入多播组才能收到消息。

3.1 多播发送方示例

// UDP多播发送示例
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>int main() {int sockfd;struct sockaddr_in multicast_addr;char *msg = "Hello UDP Multicast!";sockfd = socket(AF_INET, SOCK_DGRAM, 0);if (sockfd < 0) {perror("socket error");return -1;}memset(&multicast_addr, 0, sizeof(multicast_addr));multicast_addr.sin_family = AF_INET;multicast_addr.sin_port = htons(12345);inet_pton(AF_INET, "239.255.0.1", &multicast_addr.sin_addr);  // 多播地址，必须是224.0.0.0~239.255.255.255范围sendto(sockfd, msg, strlen(msg), 0, (struct sockaddr*)&multicast_addr, sizeof(multicast_addr));printf("UDP Multicast message sent.\n");close(sockfd);return 0;
}

3.2 多播接收方示例

接收方需要加入多播组，才能接收到该组播发送的消息。

// UDP多播接收示例
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>int main() {int sockfd;struct sockaddr_in local_addr;struct ip_mreq mreq;char buf[256];int nbytes;socklen_t addrlen;sockfd = socket(AF_INET, SOCK_DGRAM, 0);if(sockfd < 0) {perror("socket error");return -1;}// 绑定本地端口，监听多播数据memset(&local_addr, 0, sizeof(local_addr));local_addr.sin_family = AF_INET;local_addr.sin_port = htons(12345);local_addr.sin_addr.s_addr = htonl(INADDR_ANY); // 监听所有本地接口if(bind(sockfd, (struct sockaddr*)&local_addr, sizeof(local_addr)) < 0) {perror("bind error");close(sockfd);return -1;}// 加入多播组mreq.imr_multiaddr.s_addr = inet_addr("239.255.0.1"); // 多播组地址mreq.imr_interface.s_addr = htonl(INADDR_ANY);        // 本地接口if(setsockopt(sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq)) < 0) {perror("setsockopt mreq error");close(sockfd);return -1;}printf("Waiting for multicast message...\n");addrlen = sizeof(local_addr);while(1) {nbytes = recvfrom(sockfd, buf, sizeof(buf) - 1, 0, (struct sockaddr*)&local_addr, &addrlen);if(nbytes < 0) {perror("recvfrom error");break;}buf[nbytes] = '\0';printf("Received multicast message: %s\n", buf);}// 离开多播组（可选）setsockopt(sockfd, IPPROTO_IP, IP_DROP_MEMBERSHIP, &mreq, sizeof(mreq));close(sockfd);return 0;
}

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总结

通信方式	发送代码重点	需要设置	接收代码重点
单播	直接 sendto 指定目标 IP/端口	无需特殊设置	bind 监听端口，recvfrom接收
广播	设置 SO_BROADCAST 选项	需要开启广播权限	bind监听端口，recvfrom接收
多播	发送到多播组地址（224~239）	发送无需特殊设置	bind监听端口 + IP_ADD_MEMBERSHIP加入组播