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这个就跟你在头文件里#define效果是一样的,好处是方便在不同的编译配置(build configuration)下使用的比较灵活。比如FLASH如果是在预定义了,那么编译配置选择RAM的时候就可以把不需要的语句去掉。没找到这些变量也没关系,不影响阅读程序。