[网络协议]基于UDP的简单回显程序

#include<stdio.h>
#include<netinet/in.h>
#include<stdlib.h>
#include<string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include<pthread.h>
#include<strings.h>

int main()
{
    int sockfd = socket(AF_INET,SOCK_DGRAM,0);          //创建udp套接字socket得到socketfd
    struct sockaddr_in ser_addr;
    memset(&ser_addr,0,sizeof(ser_addr));
    ser_addr.sin_family = AF_INET;
    ser_addr.sin_port = htons(21);                      //这里需要绑定的是本地的ip跟端口，而不是客户端
    ser_addr.sin_addr.s_addr = inet_addr("192.168.1.109");

    int b = bind(sockfd,(struct sockaddr*)&ser_addr,sizeof(struct sockaddr_in));
    if(b == -1)
    {                                                  //判断是否绑定成功
        perror("bind() error!\n");
    }
    struct sockaddr_in cli_addr;
    int s = sizeof(struct sockaddr);
    char buf[20];
    char send[]={"over,over"};
    int ret;
    while(1)                                          //收发数据
    {
        bzero(buf,20);
        ret = recvfrom(sockfd,buf,20,0,(struct sockaddr *)&cli_addr,&s);
        if(ret < 0)
        {
            perror("send() error!\n");
        }
        printf("%s\n",buf);
        sendto(sockfd,send,strlen(send),0,(struct sockaddr *)&cli_addr,s);
    }
    close(sockfd);                                   //关闭套接字socketfd

}