Why does the global variable of VC still need extern?

Generally, you can define the global variable int inum in a CPP;

If you need to use this global variable in another CPP file, you must add a reference definition, such as extern int inum!

Suspect: since it is a global variable, it can be used in any file. Why should I add an "extern int inum" statement?

A: The scope of a global variable starts at the defined position and ends with the end of the file, that is, only the scope of the file. To extend the scope of global variables to multiple files, the extern keyword is provided in C ++. Extern keyword declaration, does not allocate memory.

Overview: Global
You also need to use extern to guard against it!

Reference: http://www.letuknowit.com/archives/87