使用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。

以下是基于C语言的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 <sys/socket.h>
#include <netinet/in.h>
#include <pthread.h>

#define BUF_SIZE 1024
#define PORT 8080
#define MAX_CLIENTS 100

void *handle_client(void *arg);

int main(int argc, char const *argv[]) {
    int server_fd, client_fd;
    struct sockaddr_in server_addr, client_addr;
    int opt = 1;
    int addr_len = sizeof(struct sockaddr_in);
    char buf[BUF_SIZE];
    int ret;

    // 创建socket
    if ((server_fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // 设置socket选项
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt)) < 0) {
        perror("setsockopt failed");
        exit(EXIT_FAILURE);
    }

    // 绑定地址
    memset(&server_addr, 0, addr_len);
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(PORT);
    if (bind(server_fd, (struct sockaddr *)&server_addr, addr_len) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // 接收数据
    pthread_t thread_id[MAX_CLIENTS];
    int i = 0;
    while (1) {
        memset(buf, 0, BUF_SIZE);
        ret = recvfrom(server_fd, buf, BUF_SIZE, 0, (struct sockaddr *)&client_addr, &addr_len);
        if (ret < 0) {
            perror("recvfrom failed");
            exit(EXIT_FAILURE);
        }

        // 处理客户端请求
        printf("Received message from %s:%d: %s\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port), buf);
        pthread_create(&thread_id[i++], NULL, handle_client, (void *)&client_fd);
    }

    return 0;
}

// 处理客户端请求
void *handle_client(void *arg) {
    int client_fd = *(int *)arg;
    char buf[BUF_SIZE];
    int ret;

    while (1) {
        memset(buf, 0, BUF_SIZE);
        ret = recv(client_fd, buf, BUF_SIZE, 0);
        if (ret < 0) {
            perror("recv failed");
            exit(EXIT_FAILURE);
        } else if (ret == 0) {
            printf("Client disconnected\n");
            break;
        }

        printf("Received message: %s\n", buf);

        ret = send(client_fd, buf, strlen(buf), 0);
        if (ret < 0) {
            perror("send failed");
            exit(EXIT_FAILURE);
        }
    }

    close(client_fd);
    return NULL;
}

客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define BUF_SIZE 1024
#define PORT 8080

int main(int argc, char const *argv[]) {
    int client_fd;
    struct sockaddr_in server_addr;
    char buf[BUF_SIZE];
    int ret;

    // 创建socket
    if ((client_fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // 设置服务器地址
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(PORT);

    // 发送数据
    while (1) {
        memset(buf, 0, BUF_SIZE);
        fgets(buf, BUF_SIZE, stdin);

        ret = sendto(client_fd, buf, strlen(buf), 0, (struct sockaddr *)&server_addr, sizeof(server_addr));
        if (ret < 0) {
            perror("sendto failed");
            exit(EXIT_FAILURE);
        }
    }

    close(client_fd);
    return 0;
}

在服务器端，我们使用`pthread_create()`函数创建线程来处理客户端请求。在客户端，我们使用`fgets()`函数从标准输入读取用户输入，并使用`sendto()`函数将数据发送到服务器。