请用C++写一段UDP通信，实现客户端发送消息，服务器响应

好的，下面是一段简单的UDP通信的示例代码：

客户端代码：

#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

using namespace std;

int main()
{
    int sockfd, n;
    char sendline[100], recvline[100];
    struct sockaddr_in servaddr;

    sockfd = socket(AF_INET, SOCK_DGRAM, 0);

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
    servaddr.sin_port = htons(9999);

    while (fgets(sendline, 100, stdin) != NULL) {
        sendto(sockfd, sendline, strlen(sendline), 0, (struct sockaddr*)&servaddr, sizeof(servaddr));
        n = recvfrom(sockfd, recvline, 100, 0, NULL, NULL);
        recvline[n] = '\0';
        cout << "recv: " << recvline << endl;
    }

    return 0;
}

服务器端代码：

#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

using namespace std;

int main()
{
    int sockfd, n;
    char recvline[100], sendline[100];
    struct sockaddr_in servaddr, cliaddr;

    sockfd = socket(AF_INET, SOCK_DGRAM, 0);

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(9999);

    bind(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr));

    while (true) {
        socklen_t len = sizeof(cliaddr);
        n = recvfrom(sockfd, recvline, 100, 0, (struct sockaddr*)&cliaddr, &len);
        recvline[n] = '\0';
        cout << "recv: " << recvline << endl;

        strcpy(sendline, "I got your message!");
        sendto(sockfd, sendline, strlen(sendline), 0, (struct sockaddr*)&cliaddr, sizeof(cliaddr));
    }

    return 0;
}

运行这两个程序，然后在客户端输入消息，服务器会响应并返回一条固定的消息。