c++ - N4713中的[cpp.cond]/2

Question

N4713中的[cpp.cond] / 2:

A defined-macro-expression evaluates to 1 if the identifier is currently defined as a macro name (that is, if it is predefined or if it has been the subject of a #define preprocessing directive without an intervening #undef directive with the same subject identifier), 0 if it is not.

我不了解上面的或。也就是说，如何在不使用#define预处理指令的情况下预定义宏名称？

Answer 1

该实现预定义了一些宏，而无需用户对其进行#define。在[cpp.predefined]中可以找到标准预定义宏名称的列表。例如，它包括__FILE__和__LINE__。