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UDP协议详细讲解及C++代码实例

一、UDP协议概述

UDP（User Datagram Protocol，用户数据报协议）是一种无连接的、简单的、基于数据报的传输层通信协议。其核心特性包括：

• 无连接：不需要建立连接即可发送数据。
• 不可靠：不保证数据包的顺序和到达。
• 高效：由于没有复杂的连接和可靠性机制，UDP传输效率较高。
• 适用场景：适用于实时性要求高、可以容忍少量数据丢失的场景，如视频流、实时游戏等。

二、UDP通信流程

1)数据传输

数据被分割为多个UDP数据报，每个数据报独立传输。

2)无连接

通信双方无需建立连接，直接发送和接收数据。

C++代码实例

1. UDP客户端代码（C++）
cpp
#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>int main() {// 创建UDP套接字int client_socket = socket(AF_INET, SOCK_DGRAM, 0);if (client_socket == -1) {std::cerr << "Failed to create socket." << std::endl;return -1;}// 设置服务器地址和端口sockaddr_in server_address{};server_address.sin_family = AF_INET;server_address.sin_port = htons(8888);server_address.sin_addr.s_addr = inet_addr("127.0.0.1");try {// 发送数据const char* message = "Hello, UDP Server!";sendto(client_socket, message, strlen(message), 0, (struct sockaddr*)&server_address, sizeof(server_address));// 接收响应char buffer[1024] = {0};socklen_t server_address_size = sizeof(server_address);int bytes_received = recvfrom(client_socket, buffer, sizeof(buffer), 0, (struct sockaddr*)&server_address, &server_address_size);if (bytes_received > 0) {std::cout << "Received from server: " << buffer << std::endl;}} catch (...) {std::cerr << "An error occurred during communication." << std::endl;}// 关闭套接字close(client_socket);return 0;
}

2. UDP服务器端代码（C++）
cpp
#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>int main() {// 创建UDP套接字int server_socket = socket(AF_INET, SOCK_DGRAM, 0);if (server_socket == -1) {std::cerr << "Failed to create socket." << std::endl;return -1;}// 绑定地址和端口sockaddr_in server_address{};server_address.sin_family = AF_INET;server_address.sin_port = htons(8888);server_address.sin_addr.s_addr = INADDR_ANY;if (bind(server_socket, (struct sockaddr*)&server_address, sizeof(server_address)) == -1) {std::cerr << "Failed to bind socket." << std::endl;close(server_socket);return -1;}std::cout << "Server is listening on port 8888..." << std::endl;try {while (true) {// 接收数据char buffer[1024] = {0};sockaddr_in client_address{};socklen_t client_address_size = sizeof(client_address);int bytes_received = recvfrom(server_socket, buffer, sizeof(buffer), 0, (struct sockaddr*)&client_address, &client_address_size);if (bytes_received > 0) {std::cout << "Received from client: " << buffer << std::endl;// 发送响应const char* response = "Hello, UDP Client!";sendto(server_socket, response, strlen(response), 0, (struct sockaddr*)&client_address, client_address_size);}}} catch (...) {std::cerr << "An error occurred in the server loop." << std::endl;}// 关闭套接字close(server_socket);return 0;
}

三、关键点解析

1） 套接字创建

socket(AF_INET, SOCK_DGRAM, 0)：创建IPv4的UDP套接字。

2）无连接特性

使用sendto()和recvfrom()发送和接收数据，无需建立连接。

3）数据传输

sendto()：发送数据到指定地址。
recvfrom()：接收数据，并获取发送方的地址信息。

四、总结

UDP协议通过无连接、简单高效的特性，适用于实时性要求高的场景。上述代码示例展示了UDP客户端和服务端的完整交互流程，适用于需要高效传输且能容忍少量数据丢失的场景。