未定义的符号与预处理器指令一起使用。

A symbol that was not defined was used with a preprocessor directive.

youdao

同时要注意，未定义的符号foo . fop . nope尽管没有赋值，但这样表示只是它本身的拼写。

Also notice that the undefined symbol foo.fop.nope simply stands for its own spelling, absent an assignment to the contrary.

youdao

But the take away for now is that if you don't clue -lcs50, -- you get some mention -- some error message -- about "undefined symbol," and that should be your clue that, "Oh it's undefined in that I haven't told the compiler that I want to link in these zeros and ones."

但现在如果你删除“-lcs50“,你们会得到一些提示--一些错误信息-,像“未定义的符号“，这可以为你提过线索，“这个没有被定义，我没有告诉编译器,把想把这个与“1“和“0“建立连接，“

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