Let’s have an example:
/* Here is a nondefining declaration of function max; */
/* it merely informs compiler that max is a function */
int
max();
/* Here is a definition of function max: */
int
max(
int
x,
int
y) {
return
(x>=y) ? x : y;
}
int
i;
/* Definition of variable i */
int
i;
/* Error: i is already defined! */
Declarations and Declarators
A declaration is a list of names. The names are sometimes referred to as declara-
tors or identifiers. The declaration begins with optional storage class specifiers,
type specifiers, and other modifiers. The identifiers are separated by commas and
the list is terminated by a semicolon.
Declarations of variable identifiers have the following pattern:
storage-class [type-qualifier] type var1 [=init1], var2 [=init2],
...;
where
var1
,
var2
,... are any sequence of distinct identifiers with optional initial-
izers. Each of the variables is declared to be of
type
; if omitted,
type
defaults to
int
. Specifier
storage-class
can take values
extern
,
static
,
register
, or
the default
auto
. Optional
type-qualifier
can take values
const
or
volatile
. For more details, refer to Storage Classes and Type Qualifiers.
Here is an example of variable declaration:
/* Create 3 integer variables called x, y, and z and
initialize x and y to the values 1 and 2, respectively: */
int
x = 1, y = 2, z;
// z remains uninitialized
These are all defining declarations; storage is allocated and any optional initializ-
ers are applied.
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