static int a;
int b;
a has internal linkage. b has extern linkage.
C99 6.2.2
6.2.2 Linkages of identifiers
1) An identifier declared in different scopes or in the same scope more than once can be
made to refer to the same object or function by a process called linkage. There are
three kinds of linkage: external, internal, and none.
2) In the set of translation units and libraries that constitutes an entire program, each
declaration of a particular identifier with external linkage denotes the same object or
function. Within one translation unit, each declaration of an identifier with internal
linkage denotes the same object or function. Each declaration of an identifier with no
linkage denotes a unique entity.
3) 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.
