The difference between global variables and global static variables

(c) static with external links; can be called in all source files; In addition to this file, other documents can be referenced by extern means;


(a) Do not worry about other source files using the same variable name, independent of each other.
(b) A static global variable defined in a source file cannot be used or modified by another source file.
(c) can only be used in this document! Static with internal links, not allowed in other files;

The difference between global variables and global static variables