实现udp服务器和客户端的通信

首先是服务器的搭建：

1.创建套接字文件 socket(AF_INET,SOCK_DGRAM,0);

2.用truct sockaddr_in此数据结构用做bind、connect、recvfrom、sendto等函数的参数，指明服务器地址信息。（truct sockaddr_in service_addr）详细配置
（truct sockaddr_in client_addr）由于不知道客户端地址信息，所以创建，用来存储等待客户端发消息从而获得的地址信息

3.将服务器地址信息绑定到套接字文件bind(socfd,(struct sockaddr*)&serv_addr,sizeof(struct sockaddr))

4.等待客户端主动连接recvfrom()

5.发送信息给客户端sendto（）

第四步放在主线程中，第五步放在子线程中完成。

程序：

 int main(int argc,char *argv[])
 {
    pthread_t tid;
    int ret=53;
    int on=1;
    char rbuff[1024]={0};

    ssize_t r_len;
    socklen_t len;
    struct sockaddr_in serv_addr;

    len = sizeof(cli_addr) ;
    bzero((char*)&cli_addr,sizeof(cli_addr));
    bzero((char*)&serv_addr,sizeof(serv_addr));

    socfd = socket(AF_INET,SOCK_DGRAM,0);
    if(socfd == -1)
    {
        printf("create socket fail\n"); 
    }
    else{printf("create socket success\n"); }
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(SERV_PORT);
    serv_addr.sin_addr.s_addr = inet_addr(SERVICE_IP);
    setsockopt(socfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on));
    ret = bind(socfd,(SA*)&serv_addr,sizeof(SA));
    if(ret == -1)
    {
        printf("bind fail\n");

    }
    else if(ret==0){printf("bind succeed\n");}
    pthread_create(&tid,NULL,pthread1,NULL);
    while(1)
    {   

        r_len = recvfrom(socfd,rbuff,sizeof(rbuff),0,(SA*)&cli_addr,&len);//can get client address infomation
        if(strncmp(rbuff,"quit",4)==0)
        {

            pthread_exit(NULL);
            break;
        }
        if(r_len == -1)
        {printf("rec error");}
        else{printf("from client:%s\n",rbuff);}
        bzero(rbuff,sizeof(rbuff));
    }
    close(socfd);
    return 0;
}

void *pthread1(void *arg)
{
    char sbuff[1024]={0};
    ssize_t s_len;
    while(1)
    {

        printf("service:");
        scanf("%s",sbuff);
        s_len = sendto(socfd,sbuff,sizeof(sbuff),0,(SA*)&cli_addr,sizeof(cli_addr));
        if(s_len == -1)
        {printf("send error");}
        //else{printf("send success\n");}
        bzero(sbuff,sizeof(sbuff));

    }
}

客户端：

1.创建套接字文件 socket(AF_INET,SOCK_DGRAM,0);

2.用truct sockaddr_in此数据结构用做bind、connect、recvfrom、sendto等函数的参数，指明服务器地址信息。（truct sockaddr_in 变量名）

3.发送信息给客户端

4.等待服务器发送信息

第三步放在主线程中，第四步放在子线程中完成。

程序：

int main(void)
{

pthread_t tid;
char sbuff[1024]={0};
ssize_t s_len;

socfd = socket(AF_INET,SOCK_DGRAM,0);
if(socfd == -1)
{
    printf("create socket fail\n"); 
}
else{printf("create success\n");}

bzero((char*)&serv_addr,sizeof(serv_addr));
//configure serv_addr
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(SERV_PORT);
//serv_addr.sin_addr.s_addr=INADDR_ANY;
serv_addr.sin_addr.s_addr = inet_addr(SERVICE_IP);
pthread_create(&tid,NULL,pthread1,NULL);
while(1)
{

    printf("client1:");
    scanf("%s",sbuff);
s_len=sendto(socfd,sbuff,sizeof(sbuff),0,(struct sockaddr*)&serv_addr,sizeof(serv_addr));///
    if(strncmp(sbuff,"quit",4)==0)
    {
        pthread_exit(NULL);
        break;
    }
    bzero(sbuff,sizeof(sbuff));
    if(s_len == -1)
    {printf("send error\n");}
    //else{printf("send succeed\n");}

}
close(socfd);
return(0);
 }

void *pthread1(void *arg)
 {
ssize_t r_len;
socklen_t len;
char rbuff[1024]={0};
len = sizeof(serv_addr);
while(1)
{

    r_len=recvfrom(socfd,rbuff,sizeof(rbuff),0,(struct sockaddr*)&serv_addr,&len);
    if(r_len == -1)
    {printf("rec error");}
    else{printf("from server:%s\n",rbuff);}
    bzero(rbuff,sizeof(rbuff));
}

}

需要注意的是：

1.端口号选取尽量大一点，以防被其他udp进程占用，0~65535，我刚开始选取666，无法实现正常功能，改成8888后能正常实现功能

2.服务器bind经常失败.解决方法：在bind设置SO_REUSEADDR套接字选项。

const int on=1;

setsockopt(listenfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on));

这个使服务端（server1）主动关闭后可以立即重启。

我是菜鸟，程序还有很多不足，见谅哈！