先看效果

程序会将收到的信息又发送给对端

流程

程序源码

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <errno.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#define HOST "192.168.1.164"                // 本机地址
#define PORT 8888                           // 端口

int main ()
{
    int sockfd;
    int ret;
    uint8_t buf[100];
    struct sockaddr_in server, peer_addr;
    socklen_t peerlen;

    peerlen = (socklen_t)sizeof(struct sockaddr);

    // 创建UDP Socket
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd == -1) 
    {
        printf("fail to creat socket.\r\n");
        exit(EXIT_FAILURE);
    }

    // 设置地址与端口到结构体
    memset(&server, 0,sizeof(server));
    server.sin_family = AF_INET;    // IPV4
    server.sin_port = htons(PORT);
    server.sin_addr.s_addr = inet_addr(HOST);

    // 绑定地址与端口信息
    ret = bind(sockfd, (struct sockaddr *)&server, sizeof(struct sockaddr));
    if (ret == -1) 
    {
        close(sockfd);
        printf("Fail to bind information.\r\n");
        exit(EXIT_FAILURE);
    }
    
    while (1)
    {
        // 非阻塞接收消息 并存储对端地址
        ret = recvfrom(sockfd, buf, 100, MSG_DONTWAIT, (struct sockaddr *)&peer_addr, &peerlen);
        if (ret > 0)
        {
            // 将消息发回对端
            sendto(sockfd, buf, ret, MSG_DONTWAIT, (struct sockaddr *)&peer_addr, peerlen);
            printf("recv[%d]: from %s:%d\r\n", ret, inet_ntoa(peer_addr.sin_addr), htons(peer_addr.sin_port));
        }
        else if (ret == 0)
        {
            close(sockfd);
            break;
        }
        else
        {
            if(errno != EINTR && errno != EWOULDBLOCK && errno != EAGAIN)
            {
                close(sockfd);
                break;
            }
        }
    }
    
    return 0;
}