Ifndef
如果未定义
🗣️ 情景例句
Yes. I'll hold. He's checking. You do?
好， 我会等。他正在查。真的有了？
I will be flying to Canada at this time tomorrow.
我将在明天这个时候飞到加拿大。
It is disturbing to think that a dangerous wild animal is still at large in the quiet countryside.
想到在宁静的乡村里有一头危险的野兽继续逍遥流窜，真令人担心。