static statics function

Static acting on function: e.g.: static void Func (void);
When using static for function definitions, it has an effect on how the function is connected, so that the function is valid only within this file and is not visible to other files. Such a function is also called a static function. The advantage of using static functions is that you do not have to worry about interfering with the functions of the same name as other files, but also a protection mechanism for the function itself.

e.g.:

If you do not add static in the func1.c its link way can be inside, func2.c can make a call, even if the invocation of the declaration is not added extern;

When you add it, you'll report undefined print.

static statics function