Ifndef
如果未定义
🗣️ 情景例句
I'm sorry, Robbie.
对不起，Robbie。
If we are bound to forgive an enemy,we are not bound to trust him.
即便我们决心宽恕敌人，也决不能相信敌人。
That's easier said than done!
说来容易做起来难哪！