阻塞模式下,send或者recv(socket类)如何返回?

各位大虾:
阻塞模式下,send或者recv(socket类)如何返回?
while(size>0)
{
len = size>BUFFSIZE?BUFFSIZE:size;
ret = recv(client,(char *)buf,len,0);
if(ret<0)
{
myfile.Close ();
closesocket(client);
dlg->MessageBox ("receive file err!","",MB_OK);
return -1;
}
myfile.Write (buf,len);
size = size - ret;
}
其中的recv函数工作在阻塞模式下,如果网络出现异常(最简单的,网络断开)如何返回??