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

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

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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