一、UDP协议核心特性
1. UDP vs TCP
| 特性 | UDP | TCP |
|---|---|---|
| 连接方式 | 无连接 | 面向连接（三次握手） |
| 可靠性 | 不保证数据到达或顺序 | 可靠传输（超时重传、顺序控制） |
| 传输效率 | 低延迟，高吞吐 | 相对较低（因握手和确认机制） |
| 适用场景 | 实时音视频、广播、在线游戏 | 文件传输、Web请求、数据库操作 |
2. UDP数据包结构
- **首部（8字节）**：
| 源端口（2） | 目标端口（2） |
| 数据包长度（2） | 校验和（2） |
- 数据载荷：最大长度受限于IPv4的MTU（通常1500字节）。
3. 不同方式介绍
单播（Unicast）：1 对 1（普通 UDP/TCP 通信）。
广播（Broadcast）：1 对同一子网内所有设备。
组播（Multicast）：1 对一组指定的设备（跨子网）。
二、UDP单播通信实现
1. UDP服务器与客户端流程
服务器：socket() → bind() → recvfrom() → sendto()
客户端：socket() → sendto() → recvfrom()
2. 完整代码示例
UDP服务器（接收并回复）
#include <iostream>
#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "ws2_32.lib")int main() {WSADATA wsaData;if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {std::cerr << "WSAStartup failed!" << std::endl;return 1;}SOCKET sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);sockaddr_in serverAddr{};serverAddr.sin_family = AF_INET;serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);serverAddr.sin_port = htons(8080);bind(sock, (sockaddr*)&serverAddr, sizeof(serverAddr));std::cout << "UDP Server listening on port 8080..." << std::endl;char buffer[1024];sockaddr_in clientAddr{};int clientAddrLen = sizeof(clientAddr);while (true) {int bytesReceived = recvfrom(sock, buffer, sizeof(buffer), 0,(sockaddr*)&clientAddr, &clientAddrLen);if (bytesReceived == SOCKET_ERROR) {std::cerr << "recvfrom failed: " << WSAGetLastError() << std::endl;continue;}char clientIp[INET_ADDRSTRLEN] = { 0 };if (InetNtopA(AF_INET, // IPv4&clientAddr.sin_addr, // 输入地址结构体clientIp, // 输出缓冲区sizeof(clientIp) // 缓冲区大小) == NULL) {std::cerr << "IP conversion failed: " << WSAGetLastError() << std::endl;strcpy_s(clientIp, "unknown"); // 错误时显示 "unknown"}std::cout << "Received " << bytesReceived << " bytes from "<< clientIp << ":" // 使用转换后的 IP 字符串<< ntohs(clientAddr.sin_port) << std::endl;// 原样返回数据sendto(sock, buffer, bytesReceived, 0,(sockaddr*)&clientAddr, clientAddrLen);}closesocket(sock);WSACleanup();return 0;
}
UDP客户端（发送消息）
#include <iostream>
#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "ws2_32.lib")int main() {WSADATA wsaData;if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {std::cerr << "WSAStartup failed!" << std::endl;return 1;}SOCKET sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);sockaddr_in serverAddr{};serverAddr.sin_family = AF_INET;inet_pton(AF_INET, "127.0.0.1", &(serverAddr.sin_addr.s_addr));serverAddr.sin_port = htons(8080);const char* message = "Hello UDP Server!";sendto(sock, message, strlen(message), 0,(sockaddr*)&serverAddr, sizeof(serverAddr));char buffer[1024];int bytesReceived = recvfrom(sock, buffer, sizeof(buffer), 0, nullptr, nullptr);if (bytesReceived > 0) {std::cout << "Server echoed: " << std::string(buffer, bytesReceived) << std::endl;}closesocket(sock);WSACleanup();return 0;
}
测试结果
三、UDP广播通信
1. 广播地址与设置
- 广播地址：255.255.255.255（全局广播）或子网广播地址（如192.168.1.255）。
- 套接字选项：启用
SO_BROADCAST。
int enable = 1;
setsockopt(sock, SOL_SOCKET, SO_BROADCAST, (char*)&enable, sizeof(enable));
2. 广播发送端代码
#include <iostream>
#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "ws2_32.lib")int main() {WSADATA wsaData;if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {std::cerr << "WSAStartup failed!" << std::endl;return 1;}SOCKET sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);// 启用广播int enable = 1;setsockopt(sock, SOL_SOCKET, SO_BROADCAST, (char*)&enable, sizeof(enable));sockaddr_in broadcastAddr{};broadcastAddr.sin_family = AF_INET;inet_pton(AF_INET, "127.0.0.1", &(broadcastAddr.sin_addr.s_addr));broadcastAddr.sin_port = htons(8080);const char* message = "Broadcast Message!";sendto(sock, message, strlen(message), 0,(sockaddr*)&broadcastAddr, sizeof(broadcastAddr));closesocket(sock);WSACleanup();return 0;
}
3. 服务器端修改部分
std::cout << "Received " << bytesReceived << " bytes from "<< clientIp << ":" // 使用转换后的 IP 字符串<< ntohs(clientAddr.sin_port) << std::endl;std::cout << "Datas:" << std::string(buffer, bytesReceived) << std::endl;
4. 测试结果
四、UDP组播（Multicast）
1. 组播地址范围
- IPv4：224.0.0.0 ~ 239.255.255.255（如239.255.0.1）。
2. 接收端
#include <iostream>
#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "ws2_32.lib")int main() {WSADATA wsaData;if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {std::cerr << "WSAStartup failed!" << std::endl;return 1;}// 创建 UDP 套接字SOCKET sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);if (sock == INVALID_SOCKET) {std::cerr << "socket() failed: " << WSAGetLastError() << std::endl;WSACleanup();return 1;}// 设置端口复用（允许其他进程绑定相同端口）int reuse = 1;if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR,(char*)&reuse, sizeof(reuse)) == SOCKET_ERROR) {std::cerr << "setsockopt(SO_REUSEADDR) failed: " << WSAGetLastError() << std::endl;closesocket(sock);WSACleanup();return 1;}// 绑定到本地端口sockaddr_in localAddr{};localAddr.sin_family = AF_INET;localAddr.sin_addr.s_addr = htonl(INADDR_ANY);localAddr.sin_port = htons(8080);if (bind(sock, (sockaddr*)&localAddr, sizeof(localAddr)) == SOCKET_ERROR) {std::cerr << "bind() failed: " << WSAGetLastError() << std::endl;closesocket(sock);WSACleanup();return 1;}// 加入组播组ip_mreq mreq{};if (inet_pton(AF_INET, "239.255.255.250", &(mreq.imr_multiaddr.s_addr)) != 1) {std::cerr << "inet_pton() failed for multicast address" << std::endl;closesocket(sock);WSACleanup();return 1;}mreq.imr_interface.s_addr = htonl(INADDR_ANY); // 使用默认网络接口if (setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP,(char*)&mreq, sizeof(mreq)) == SOCKET_ERROR) {std::cerr << "setsockopt(IP_ADD_MEMBERSHIP) failed: " << WSAGetLastError() << std::endl;closesocket(sock);WSACleanup();return 1;}std::cout << "Listening for multicast on 239.255.255.250:8080..." << std::endl;char buffer[1024];sockaddr_in senderAddr{};int senderAddrLen = sizeof(senderAddr);while (true) {// 接收数据int bytesReceived = recvfrom(sock, buffer, sizeof(buffer) - 1, 0,(sockaddr*)&senderAddr, &senderAddrLen);if (bytesReceived == SOCKET_ERROR) {std::cerr << "recvfrom() failed: " << WSAGetLastError() << std::endl;continue;}// 显示来源信息char senderIp[INET_ADDRSTRLEN] = { 0 };inet_ntop(AF_INET, &senderAddr.sin_addr, senderIp, INET_ADDRSTRLEN);std::cout << "Received " << bytesReceived << " bytes from "<< senderIp << ":" << ntohs(senderAddr.sin_port) << std::endl;// 安全处理数据（防止缓冲区溢出）buffer[bytesReceived] = '\0'; // 添加字符串终止符std::cout << "Data: " << buffer << std::endl;}// 退出时清理（虽然 while(true) 会阻止执行到这里）closesocket(sock);WSACleanup();return 0;
}
3. 发送端
#include <iostream>
#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "ws2_32.lib")int main() {// 初始化 WinsockWSADATA wsaData;if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {std::cerr << "WSAStartup failed: " << WSAGetLastError() << std::endl;return 1;}// 创建 UDP 套接字SOCKET sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);if (sock == INVALID_SOCKET) {std::cerr << "socket() failed: " << WSAGetLastError() << std::endl;WSACleanup();return 1;}// 设置组播 TTL（控制传输范围）int ttl = 32;if (setsockopt(sock, IPPROTO_IP, IP_MULTICAST_TTL,(char*)&ttl, sizeof(ttl)) == SOCKET_ERROR) {std::cerr << "setsockopt(IP_MULTICAST_TTL) failed: " << WSAGetLastError() << std::endl;closesocket(sock);WSACleanup();return 1;}// 构建组播目标地址sockaddr_in multicastAddr{};multicastAddr.sin_family = AF_INET;multicastAddr.sin_port = htons(8080); // 目标端口// 转换组播地址if (inet_pton(AF_INET, "239.255.255.250", &multicastAddr.sin_addr.s_addr) != 1) {std::cerr << "inet_pton() failed for multicast address" << std::endl;closesocket(sock);WSACleanup();return 1;}// 发送数据const char* msg = "Hello Multicast!";int msgLen = static_cast<int>(strlen(msg));int bytesSent = sendto(sock, msg, msgLen, 0,(sockaddr*)&multicastAddr, sizeof(multicastAddr));if (bytesSent == SOCKET_ERROR) {std::cerr << "sendto() failed: " << WSAGetLastError() << std::endl;}else if (bytesSent != msgLen) {std::cerr << "sendto() partial send: " << bytesSent << "/" << msgLen << std::endl;}else {std::cout << "Successfully sent " << bytesSent<< " bytes to multicast group 239.255.255.250:8080" << std::endl;}// 清理资源closesocket(sock);WSACleanup();return 0;
}
4. 测试结果
