Programming in C

6.0 Storage Classes and Scope 453

Ta ble A.6 Va riables: Summary of Storage Classes, Scope, and Initialization

If Storage And Variable Then it can be And can be

Class is is declared referenced initialized with Comments

static Outside any Anywhere Constant Variables are

BLOCK within the file expression only initialized

Inside a BLOCK Within the only once at

BLOCK the start of pro-

gram execution;

values are

retained through

BLOCKs;

default value is 0

extern Outside any Anywhere within Constant Variable must

BLOCK the file expression only be declared

Inside a BLOCK Within the in at least

BLOCK one place with-

out the extern

keyword, or in

one place using

the keyword

externand

assigned an ini-

tial value

auto Inside a BLOCK Within the Any valid Variable is

BLOCK expression initialized each

time the

BLOCK is

entered; no

default value

register Inside a BLOCK Within the Any valid Assignment

BLOCK expression to register not

guaranteed;

varying restric-

tions on types of

variables that

can be declared;

cannot take the

address of a reg-

ister variable;

initialized each

time BLOCK is

entered; no

default value

20 0672326663 AppA 6/10/04 2:01 PM Page 453