5.11  Storage Classes

•      Storage class specifiers

–    Storage duration – how long an object exists in memory

–    Scope – where object can be referenced in program

–    Linkage – specifies the files in which an identifier is known (more in Chapter 14)

•      Automatic storage

–    Object created and destroyed within its block

–   auto: default for local variables

auto double x, y;

–   register: tries to put variable into high-speed registers

•    Can only be used for automatic variables

register int counter = 1;

•      Static storage 

–    Variables exist for entire program execution

–    Default value of zero

–   static: local variables defined in functions. 

•    Keep value after function ends

•    Only known in their own function

–   extern: default for global variables and functions

•    Known in any function