How extern is used?

How extern can be used?

In which file the variable without extern to be declared?

Or there is no such restrictions?

 RE: How extern is used?

How extern can be used?

Any C textbook should be able to explain that.

Extern is used to access global variables/functions that have been declared in another module/file.

In which file the variable without extern to be declared?

In any file. As long as there's no ambiguity.

 RE: How extern is used?

http://c-faq.com/cpp/hfiles.html

http://c-faq.com/decl/extern.html

http://c-faq.com/decl/extarraysize.html

http://c-faq.com/aryptr/aryptr1.html

 RE: How extern is used?

"Extern is used to access global variables/functions that have been declared in another module/file."

Actually, the global variables/functions must be defined in another module/file - extern provides just a declaration.

The definition is what actually creates the "object"; ie, allocates memory or generates code.
Every "object" must have exactly one definition.

A declaration simply provides information that an "object" is defined elsewhere.
An "object" may have many declarations.