ioctl(fd,FIONREAD,&nread) nread == 0

for  (fd  =   0 ;fd  <  FD_SETSIZE;fd ++ )
... {
        if (FD_ISSET(fd,&testSet))
        ...{
            int nread;
            ioctl(fd,FIONREAD,&nread);
            if (nread == 0)
            ...{
                printf("connect close ");   //对方已经断开连接
            }
            else
            ...{
                int recvBuffSize = strlen(recvBuff);
                read(fd,recvBuff,recvBuffSize);  
                        }
                }
}