在C ++中，全局/命名空间范围内的 static 表示该功能/变量仅在定义该功能/变量的翻译单元中使用，不在其他翻译单位中.

In C++, static at global/namespace scope means the function/variable is only used in the translation unit where it is defined, not in other translation units.

在这里，您尝试使用的静态函数与定义其定义单元( File.cpp )不同的转换单元( Main.cpp ).

Here you are trying to use a static function from a different translation unit (Main.cpp) than the one in which it is defined (File.cpp).

删除 static ，它应该可以正常工作.

Remove the static and it should work fine.