C Declarations: A Short
Primer
Based on an article by
Greg Comeau,
published in the September
1998 edition of the Microsoft Systems Journal
In the ariticle "A Guide to Understanding Even the Most
Complex C Declarations", Greg Comeau presents a set of rules that
can be applied to interpret any C declaration however complex it may
seem. While the rules are intuitive and might appeal to most advanced C
programmers, the beginner may find them difficult to grasp. He does
however start the article by presenting a simple ruleset to read and
write Kernighan and Ritchie (of the famous book, The C Progamming
Language, 1978) style declarations.
In this Primer I will present these rules
and elaboarte on them with examples.
Here is the standard sytax for C Declarations:
The sytax of a C declaration is of the form:
storageclass
type qualifier declarator = initializer;
where storageclass
is only one of the following:
typedef
extern
static
auto
register
A type
could be one or more of the following:
void
char
short, int,
long
float, double
signed,
unsigned
struct ...
union ...
typedef type
A qualifier could be one or more of the following:
const
volatile
A declarator contains an identifier and one or more, or none at all, of
the following in a variety of combinations:
*
()
[]
possibly grouped within parentheses to create different bindings 
The term storageclass refers to the method by which an object is
assigned space in memory. Chapter 4 of the C Primer gives detailed
descriptions of what each of the storageclasses mean. Suffice it to
say that understanding what is being declared has no bearing on the storageclass, as it specifically tells you where it
is being declared and assigned space in memory. Also, qualifiers
(const, volatile) refer respectively to the nonmodifiability of an
entity, and the fact that the entity in question is modified
elsewhere. Therefore, henceforth we will ignore these two pieces
of information.
The above definition simply says what a declaration ought to look like
(the syntax that is). The key phrase in the above definition is "to
create different bindings". What this means is, to give different
interpretations to the declaration based on parenthesizing the
declaration. All one has to understand any complex C declaration then,
is to know that these declarations are based on the C operator
precedence chart, the same one you use to evaluate expressions in C:
Precedence 
Operators 
Associativity 
highest 
() []
. > ++(postfix)
(postfix) 
left to right 

++(prefix) (prefix)
!~ sizeof(type)
+(unary) (unary)
&(address) *(dereference) 
right to left 

*
/ % 
left to right 

+  
left to right 

<<
>> 
left to right 

<
<= > >= 
left to right 

== != 
left to right 

& 
left to right 

^ 
left to right 

 
left to right 

&& 
left to right 

 
left to right 

? : 
right to left 

= +=
=
*= /=
%= <<=
>>= =
&= ^=

right to left 
lowest 
, 
left to right 
This chart is complicated because it gives the precedence and
associativity of all C operators. With declarations, we are only
dealing
with unary tokens (unary operators need only one operand) so it is a
lot simpler The operators of interest to us are marked in red in the
above table.
So, here then are the rules
for reading and writing C declarations:
 Parenthesize declarations as if they were expressions.
 Locate the innermost parentheses.
 Say "identifier is" where the identifier is the name of the
variable.

Say "an array of X" if you see [X].
 Say "a pointer to" if you see *.
 Say "A function returning" if you see ();
 Move to the next set of parentheses.
 If more, go back to 3.
 Else, say "type" for the remaining type left (such as short
int)

Here are some examples to clarify this process:
Example 1:
int i;
The parenthesization of the above declaration is:
int (i); {1}
Applying the rules (see above) to the parenthesized expression can be done as follows:
The innermost parentesis is (i) {2}
i is the variable name, therefore we say "i is ..." {3}
No more parentheses left so we say "an int". {4,5,6}
That is, "i is an int"
Example 2:
int *i;
The parenthesization of the above declaration is:
int (*(i)); {1}
Applying the rules (see above) to the parenthesized expression can be done as follows:
The innermost parentesis is (i) {2}
i is the variable name, therefore we say "i is ..." {3}
Move to the next set of parenthesis: (*(i)) {4}
Go back to step 3. {5}
We say "a pointer to" since we see a * {3.b}
No more parentheses left so we say "an int". {4,5,6}
That is, "i is a pointer to an int"
Example 3:
int *i[3];
The parenthesization of the above declaration is:
int (*((i)[3])); {1} // Note that () and [] have the same
// precedence but we deal with them from left to right.
Applying the rules (see above) to the parenthesized expression can be done as follows:
The innermost parentesis is (i) {2}
i is the variable name, therefore we say "i is ..." {3}
Move to the next set of parenthesis: ((i)[3]) {4}
Go back to step 3. {5}
We say "an array of 3 ..." since we see a [3] {3.a}
Move to the next set of parenthesis: (*((i)[3])) {4}
Go back to step 3. {5}
We say "pointers to ..." since we see a * {3,b}
No more parentheses left so we say "ints". {4,5,6}
That is, "i is an array of 3 pointers to ints"
Example 4:
int (*i)[3];
The parenthesization of the above declaration is:
int ((*(i))[3]); {1} // Note that parentheses are valid tokens
// in a declaration and therefore must be
// be left in place when finding the final
// parenthesization
Applying the rules (see above) to the parenthesized expression can be done as follows:
The innermost parentesis is (i) {2}
i is the variable name, therefore we say "i is ..." {3}
Move to the next set of parenthesis: (*(i)) {4}
Go back to step 3. {5}
We say "a pointer to ..." since we see a * {3.b}
Move to the next set of parenthesis: ((*(i))[3]) {4}
Go back to step 3. {5}
We say "an array of 3 ..." since we see a [3] {3.a}
No more parentheses left so we say "ints". {4,5,6}
That is, "i is a pointer to an array of 3 ints"
Example 5:
int *i();
The parenthesization of the above declaration is:
int (*((i)())); {1} // Note that * has a lower precedence than
// parentheses, ()
Applying the rules (see above) to the parenthesized expression can be done as follows:
The innermost parentesis is (i) {2}
// One could argue that () is also the innermost parenthesis but
// it does not contain anything so we know it must indicate
// a function
i is the variable name, therefore we say "i is ..." {3}
Move to the next set of parenthesis: ((i)()) {4}
Go back to step 3. {5}
We say "a function returning" since we see a () {3.c}
Move to the next set of parenthesis: (*((i)())) {4}
Go back to step 3. {5}
We say "a pointer to ..." since we see a * {3.b}
No more parentheses left so we say "an int". {4,5,6}
That is, "i is a function returning a pointer to an int"
Example 6:
int (*i)();
The parenthesization of the above declaration is:
int ((*(i))()); {1} // Note that parentheses are valid tokens
// in a declaration and therefore must be
// be left in place when finding the final
// parenthesization
Applying the rules (see above) to the parenthesized expression can be done as follows:
The innermost parentesis is (i) {2}
i is the variable name, therefore we say "i is ..." {3}
Move to the next set of parenthesis: (*(i)) {4}
Go back to step 3. {5}
We say "a pointer to" since we see a * {3.b}
Move to the next set of parenthesis: ((*(i))()) {4}
Go back to step 3. {5}
We say "a function returning" since we see a () {3.c}
No more parentheses left so we say "an int". {4,5,6}
That is, "i is a pointer to a function returning an int"
This is the pretty much all one needs to know to read and write declarations in C.