Storage-Class Specifiers with Function Declarations
You can use either the static or the extern storage-class specifier in function declarations. Functions always have global lifetimes.
Microsoft Specific
Function declarations at the internal level have the same meaning as function declarations at the external level. This means that a function is visible from its point of declaration throughout the rest of the translation unit even if it is declared at local scope.
END Microsoft Specific
The visibility rules for functions vary slightly from the rules for variables, as follows:
A function declared to be static is visible only within the source file in which it is defined. Functions in the same source file can call the static function, but functions in other source files cannot access it directly by name. You can declare another static function with the same name in a different source file without conflict.
Functions declared as extern are visible throughout all source files in the program (unless you later redeclare such a function as static). Any function can call an extern function.
Function declarations that omit the storage-class specifier are extern by default.
Microsoft Specific
Microsoft allows redefinition of an extern identifier as static.
END Microsoft Specific