C Programming

Function definitions have the form
    function-definition:
      declaration-specifiersopt declarator declaration-listopt compound-statement
The only storage-class specifiers allowed among the declaration specifiers are extern or static; see Par.A.11.2 for the distinction between them. (more…)

External declarations specify the characteristics of objects, functions and other identifiers. The term “external” refers to their location outside functions, and is not directly connected with the extern keyword; the storage class for an externally-declared object may be left empty, or it may be specified as extern or static. (more…)

A program need not all be compiled at one time: the source text may be kept in several files containing translation units, and precompiled routines may be loaded from libraries. Communication among the functions of a program may be carried out both through calls and through manipulation of external data.

Therefore, there are two kinds of scope to consider: first, the lexical scope of an identifier which is the region of the program text within which the identifier’s characteristics are understood; and second, the scope associated with objects and functions with external linkage, which determines the connections between identifiers in separately compiled translation units.

dentifiers fall into several name spaces that do not interfere with one another; the same identifier may be used for different purposes, even in the same scope, if the uses are in different name spaces. These classes are: objects, functions, typedef names, and enum constants; labels; tags of structures or unions, and enumerations; and members of each structure or union individually. (more…)