Ifndef
如果未定义
🗣️ 情景例句
There are thirty-three thousand three hundred and thirty-three feathers on that bird's throat.
那只画眉鸟的喉咙上有三万三千三百三十片羽毛。
You're not worth my time.
我才懒得理你。
It's supposed to start at 6:30 sharp, but I doubt it will.
应该是六点半整的，但是我觉得够呛。