服务器端：

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<string.h>
 
#define MYPORT 8887
 
 
#define ERR_EXIT(m) \
    do { \
    perror(m); \
    exit(EXIT_FAILURE); \
    } while (0)
 
void echo_ser(int sock)
{
    char recvbuf[1024] = {0};
    struct sockaddr_in peeraddr;
    socklen_t peerlen;
    int n;
    
    while (1)
    {
        
        peerlen = sizeof(peeraddr);
        memset(recvbuf, 0, sizeof(recvbuf));
        n = recvfrom(sock, recvbuf, sizeof(recvbuf), 0,
                     (struct sockaddr *)&peeraddr, &peerlen);
        if (n <= 0)
        {
            
            if (errno == EINTR)
                continue;
            
            ERR_EXIT("recvfrom error");
        }
        else if(n > 0)
        {
            printf("接收到的数据：%s\n",recvbuf);
            sendto(sock, recvbuf, n, 0,
                   (struct sockaddr *)&peeraddr, peerlen);
            printf("回送的数据：%s\n",recvbuf);
        }
    }
    close(sock);
}
 
int main(void)
{
    int sock;
    if ((sock = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
        ERR_EXIT("socket error");
    
    struct sockaddr_in servaddr;
    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(MYPORT);
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    
    printf("监听%d端口\n",MYPORT);
    if (bind(sock, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
        ERR_EXIT("bind error");
    
    echo_ser(sock);
    
    return 0;
}

客户端：

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
 
#define MYPORT 8887
char* SERVERIP = "127.0.0.1";
 
#define ERR_EXIT(m) \
    do \
{ \
    perror(m); \
    exit(EXIT_FAILURE); \
    } while(0)
 
void echo_cli(int sock)
{
    struct sockaddr_in servaddr;
    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(MYPORT);
    servaddr.sin_addr.s_addr = inet_addr(SERVERIP);
    
    int ret;
    char sendbuf[1024] = {0};
    char recvbuf[1024] = {0};
    while (fgets(sendbuf, sizeof(sendbuf), stdin) != NULL)
    {
        
        printf("向服务器发送：%s\n",sendbuf);
        sendto(sock, sendbuf, strlen(sendbuf), 0, (struct sockaddr *)&servaddr, sizeof(servaddr));
        
        ret = recvfrom(sock, recvbuf, sizeof(recvbuf), 0, NULL, NULL);
        if (ret == -1)
        {
            if (errno == EINTR)
                continue;
            ERR_EXIT("recvfrom");
        }
        printf("从服务器接收：%s\n",recvbuf);
        
        memset(sendbuf, 0, sizeof(sendbuf));
        memset(recvbuf, 0, sizeof(recvbuf));
    }
    
    close(sock);
    
    
}
 
int main(void)
{
    int sock;
    if ((sock = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
        ERR_EXIT("socket");
    
    echo_cli(sock);
    
    return 0;
}