用C语言编写一个udp通信程序，包含服务器和客户端代码，服务器端实现多线程编程。

好的，以下是一个简单的UDP通信程序，包含服务器和客户端代码，服务器端实现了多线程编程。

服务器端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <pthread.h>

#define MAXBUF 1024
#define PORT 8888

void *handle_client(void *arg)
{
    int client_socket = *(int*)arg;
    struct sockaddr_in client_addr;
    socklen_t client_addr_size = sizeof(client_addr);

    while(1) {
        char buffer[MAXBUF+1];
        memset(buffer, 0, sizeof(buffer));
        ssize_t len = recvfrom(client_socket, buffer, sizeof(buffer)-1, 0, (struct sockaddr*)&client_addr, &client_addr_size);
        if(len == -1) {
            perror("recvfrom error");
            break;
        }
        if(len == 0) {
            printf("client closed\n");
            break;
        }
        printf("Received from %s:%d: %s", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port), buffer);
        sendto(client_socket, buffer, strlen(buffer), 0, (struct sockaddr*)&client_addr, client_addr_size);
    }

    close(client_socket);
    free(arg);
    pthread_exit(NULL);
}

int main()
{
    int server_socket;
    struct sockaddr_in server_addr;

    // 创建套接字
    server_socket = socket(AF_INET, SOCK_DGRAM, 0);
    if(server_socket == -1) {
        perror("socket error");
        exit(EXIT_FAILURE);
    }

    // 绑定地址和端口
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY); // 任意本地地址
    server_addr.sin_port = htons(PORT);
    if(bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1) {
        perror("bind error");
        exit(EXIT_FAILURE);
    }

    printf("Server started on %s:%d\n", inet_ntoa(server_addr.sin_addr), ntohs(server_addr.sin_port));

    // 循环处理客户端请求
    while(1) {
        // 接收客户端连接
        int *client_socket = (int*)malloc(sizeof(int));
        *client_socket = accept(server_socket, NULL, NULL);
        if(*client_socket == -1) {
            perror("accept error");
            continue;
        }

        // 创建线程处理客户端请求
        pthread_t tid;
        if(pthread_create(&tid, NULL, handle_client, client_socket) != 0) {
            perror("pthread_create error");
            continue;
        }
        pthread_detach(tid); // 线程结束时自动回收资源
    }

    // 关闭服务器套接字
    close(server_socket);

    return 0;
}

客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#define MAXBUF 1024
#define PORT 8888

int main()
{
    int client_socket;
    struct sockaddr_in server_addr;

    // 创建套接字
    client_socket = socket(AF_INET, SOCK_DGRAM, 0);
    if(client_socket == -1) {
        perror("socket error");
        exit(EXIT_FAILURE);
    }

    // 设置服务器地址和端口号
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = inet_addr("127.0.0.1"); // 服务器IP地址
    server_addr.sin_port = htons(PORT);

    // 循环处理用户输入
    while(1) {
        // 读取用户输入
        char buffer[MAXBUF+1];
        printf("Enter message to send: ");
        fgets(buffer, sizeof(buffer), stdin);
        if(feof(stdin)) {
            break;
        }

        // 发送数据
        if(sendto(client_socket, buffer, strlen(buffer), 0, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1) {
            perror("sendto error");
            continue;
        }

        // 接收数据
        memset(buffer, 0, sizeof(buffer));
        ssize_t len = recvfrom(client_socket, buffer, sizeof(buffer)-1, 0, NULL, NULL);
        if(len == -1) {
            perror("recvfrom error");
            continue;
        }
        if(len == 0) {
            printf("server closed\n");
            break;
        }
        printf("Received from server: %s", buffer);
    }

    // 关闭客户端套接字
    close(client_socket);

    return 0;
}

在运行程序前，需要在终端中启动服务器端程序：

$ gcc -o server server.c -lpthread
$ ./server

然后在另一个终端中启动客户端程序：

$ gcc -o client client.c
$ ./client

接着，客户端会要求您输入要发送的消息，您可以输入任何内容并按回车键发送。服务器将收到该消息并发送一个确认消息。客户端将收到确认消息并输出它们。