What is external linkage and internal linkage?

Question

I want to understand the external linkage and internal linkage and their difference.

I also want to know the meaning of

const va

Answer 1

Basically

• extern linkage variable is visible in all files
• internal linkage variable is visible in single file.

Explain: const variables internally link by default unless otherwise declared as extern

1. by default, global variable is external linkage
2. but, const global variable is internal linkage
3. extra, extern const global variable is external linkage

A pretty good material about linkage in C++

http://www.goldsborough.me/c/c++/linker/2016/03/30/19-34-25-internal_and_external_linkage_in_c++/