Linux之判断socket是否断开

1.方式一：
int rv_len;
socklen_t val;
rv_len = sizeof(val);

int ret = getsockopt(client_sockfd, SOL_SOCKET, SO_SNDBUF, &val, (unsigned int*)&rv_len);

if( ret == -1){
 //socket断开
}

2.方式二
len = recv(client_sockfd, rev_buf, sizeof(rev_buf), MSG_DONTWAIT);
if(len == 0){
  //socket断开
}