sock = socket(AF_INET,SOCK_STREAM,0);
//设置套接口的选项 SO_REUSEADDR 允许在同一个端口启动服务器的多个实例
//setsockopt的第二个参数SOL SOCKET 指定系统中，解释选项的级别 普通套接字
setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,(char*)&optval,sizeof(optval));
bind(sock,(struct sockaddr *)&server_addr,sizeof(server_addr);
listen(sock,MAXCLINE);
while()
{
    select();//消除accept阻塞
    
    new_fd = accept(sock,(struct sockaddr *)&client_addr,&sin_size);

}

linger m_sLinger;
m_sLinger.l_onoff = 1;  // (在closesocket()调用,但是还有数据没发送完毕的时候容许逗留)
m_sLinger.l_linger = 0; // (容许逗留的时间为0秒)
if(setsockopt(sock,SOL_SOCKET,SO_LINGER,(const char*)&m_sLinger,sizeof(linger)) < 0)
//这样设置是不是就是closesocket时候直接就关闭了 没有逗留时间啊？

ioctlsocket ( sock,FIONBIO,&ch);   //这里设置非阻塞后下面的recv()也都是非阻塞了吗？
ioctlsocket ( sock,FIONREAD,&templen);   //这个也不懂参数是什么意思 msdn写的太不让人明白了

       int accept4(int sockfd, struct sockaddr *addr,
                   socklen_t *addrlen, int flags);
       If flags is 0, then accept4() is the same as accept().  The following values can be bitwise ORed in flags to obtain different behavior:

       SOCK_NONBLOCK   Set the O_NONBLOCK file status flag on the new open file description.  Using this flag saves extra calls to fcntl(2) to achieve the same
                       result.