For a function, the storage class specifier determines
the linkage of the function. By default, function definitions have
external linkage, and can be called by functions defined in other
files. 
An exception is inline functions, which are treated
by default as having internal linkage; see Linkage of inline functions for more information. 
A storage class specifier may be used in both function
declarations and definitions. The only storage class options
for functions are:
- static
- extern