That is, a variable name should not be passed to a preprocessor directive and a symbol can only be evaluated by a preprocessor directive.
即，不应将变量名传递到预处理器指令，并且只能用预处理器指令计算符号。
This point in the source file is usually marked by a lexeme that is not consumed as a token by the preprocessor, meaning one that is not a preprocessor directive.
源文件中的这个点通常由一个词素进行标记，而预处理程序不会使用该词素作为一个语言符号，这表示它并不是一项预处理程序指令。
A. This is a directive to the preprocessor, which runs when you call your compiler.
这是给预处理器的一个指示，当你调用编译器的时候运行。
A. This is a directive to the preprocessor, which runs when you call your compiler.
这是给预处理器的一个指示，当你调用编译器的时候运行。
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