Question

I have a static unsigned long gVar; which is global declared in server.cc file.
But when i try to use it in other file using extern unsigned long gVar; , it gives error :

unresolved external symbol "unsigned long gVar". Can you please tell me how to extern a static variable, as i am able to extern other variables from that file except this one.

Answer 1

You cannot use static and extern together.
If you want to use the variable in other files just remove the static and just declare it as extern.

Why you cannot use static and extern together?

static implies Internal linkage, while extern implies External linkage.

Internal Linkage means that the symbol is accessible only in the Translation unit in which it was declared, while External Linkage implies the symbol should be visible in all files accross your project, clearly, they are mutually exclusive.