If the declaration of a file-scope identifier for an object or a function contains the storage-class-specifier static, the identifier has internal linkage. Otherwise, the identifier has external linkage. See Storage Classes for a discussion of the storage-class-specifier nonterminal.

Within one translation unit, each instance of an identifier with internal linkage denotes the same identifier or function. Internally linked identifiers are unique to a translation unit.

Using extern to Specify Linkage