设置非阻塞的recvfrom

 int iMode= 1; //1,非阻塞；0,阻塞
  ioctlsocket(socketc,FIONBIO,(u_long FAR*) &iMode);//非阻塞设置

  n=recvfrom(socket,rbuf,sizeof(szbuf),0,(SOCKADDR*)&addr,&len);

int ioctlsocket (
  SOCKETs,        
  longcmd,        
  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.