udpserver.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。


#include <cstring>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>
#include <stdlib.h>

#pragma comment(lib,"ws2_32.lib")

#define BUF_SIZE 1024

int main()
{
    WSADATA wsa;
    int err = WSAStartup(MAKEWORD(2, 2), &wsa);
    if (err != 0) {
        printf("failed to init wsdata! Error Code : %d", WSAGetLastError());
        return 1;
    }

    SOCKET sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (sock == INVALID_SOCKET)
    {
        printf("failed to create socket! Error Code : %d", WSAGetLastError());
        WSACleanup();
        return 1;
    }

    // bind socket
    sockaddr_in server_addr;
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    server_addr.sin_port = htons(1234);
    if (bind(sock, (sockaddr*)&server_addr, sizeof(server_addr)) == SOCKET_ERROR)
    {
        printf("failed to bind sock! Error Code : %d", WSAGetLastError());
        closesocket(sock);
        WSACleanup();
        return 1;
    }

    printf("listening to data from...\n");

    // receive UDP 数据包 and send msg
    char buf[BUF_SIZE] = { 0 };
    sockaddr_in client_addr;
    int len = sizeof(client_addr);
    while (true) {
        int n = recvfrom(sock, buf, BUF_SIZE - 1, 0, (sockaddr*)&client_addr, &len);
        
        if (n == SOCKET_ERROR)
        {
            printf("failed  to recv data! Error Code : %d", WSAGetLastError());
            continue;
        }
        printf("message content: %s\n", buf);
        if (buf[0] == 'q') {
            printf("Exiting...");
            break;
        }

        buf[n] = '\0';

        char ip[16];
        memset(ip, 0, sizeof(ip));
        inet_ntop(AF_INET, &client_addr.sin_addr, ip, sizeof(ip));
        printf("Server listening on [%s:%d]\n", ip, ntohs(server_addr.sin_port));

        const char* reply = "Hello from server!";
        if (sendto(sock, reply, strlen(reply), 0, (sockaddr*)&client_addr, sizeof(client_addr)) == SOCKET_ERROR)
        {
            printf("failed to sendto server! Error Code : %d", WSAGetLastError());
            continue;
        }
        printf("reply sent!\n");
    }

    // cleanup source
    closesocket(sock);
    WSACleanup();
    return 0;
}