UDP编程

服务端代码：

#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <time.h>
#include <string.h>
#define TIME_PORT 9090
#define DATA_SIZE 256

int main()
{
        int sock_fd;
        struct sockaddr_in local;
        struct sockaddr_in from;
        int n;
        socklen_t fromlen;
        char buff[DATA_SIZE];
        time_t cur_time;
        sock_fd = socket(AF_INET,SOCK_DGRAM,0);
        local.sin_family = AF_INET;
        local.sin_port = htons(TIME_PORT);		//监听端口
        local.sin_addr.s_addr = INADDR_ANY;		//本机
        memset(local.sin_zero,0,8);
        if(0 != bind(sock_fd,(struct sockaddr *)&local,sizeof(local))){
                perror("bind socket error!");
                close(sock_fd);
                return -1;
        }
        printf("Bind socket\n");
        fromlen = sizeof(from);
		 while(1){
                n = recvfrom(sock_fd,buff,sizeof(buff),0,(struct sockaddr *)&from,&fromlen);		//接收数据
                if(n > 0){
                        buff[n] = '\0';																										//设置字符串结束符
                        printf("Get Msg From %s : %s\n",inet_ntoa(from.sin_addr),buff);				//将32位IP地址转化为a.b.c.d
                }
                if(0 == strncmp(buff,"quit",4))																				//判断是否退出
                        break;
                if(0 == strncmp(buff,"time",4)){																			//判断是否请求时间
                       cur_time = time(NULL);																				//生成当前时间的字符串
                        strcpy(buff,asctime(gmtime(&cur_time)));													
                        sendto(sock_fd,buff,sizeof(buff),0,(struct sockaddr *)&from,fromlen);		//发送时间给客户端
                }
        }
        close (sock_fd);
        return 0;
}

客户端：

#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <time.h>
#include <string.h>
#define TIME_PORT 9090
#define DATA_SIZE 256
int main()
{
        int sock_fd;
        struct sockaddr_in serv;
        int n;
        socklen_t servlen;
        char buff[DATA_SIZE];
        sock_fd = socket(AF_INET,SOCK_DGRAM,0);
        serv.sin_family = AF_INET;
        serv.sin_port = htons(TIME_PORT);
        serv.sin_addr.s_addr = INADDR_ANY;
        servlen = sizeof(serv);
        strcpy(buff,"time");
        if(-1 == sendto(sock_fd,buff,sizeof(buff),0,(struct sockaddr *)&serv,servlen)){                      			//发送请求
                perror("send data");
                close(sock_fd);
                return 0;
        }
        printf("send time request\n");
        n = recvfrom(sock_fd,buff,sizeof(buff),0,(struct sockaddr *)&serv,&servlen);					//接受返回
        buff[n] = '\0';
        printf("time from server: %s\n",buff);
        /*退出连接*/
        strcpy(buff,"quit");
        if(-1 == sendto(sock_fd,buff,sizeof(buff),0,(struct sockaddr *)&serv,servlen)){
                perror("send data");
                close(sock_fd);
                return 0;
        }
        printf("send quit command\n");
        close(sock_fd);
        return 0;

}