int iMode = 1; //0：阻塞
  ioctlsocket(socketc,FIONBIO, (u_long FAR*) &iMode);//非阻塞设置
  rs=recvfrom(socketc,rbuf,sizeof(rbuf),0,(SOCKADDR*)&addr,&len);

​​int ioctlsocket (

  SOCKET s,         
  long cmd,         
  u_long FAR* argp  
);

​​


s

[in] A descriptor identifying a socket.


cmd

[in] The command to perform on the socket s.


argp

[in/out] A pointer to a parameter for cmd. 
​​