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What is indirection
operator? Give an example.
The
address of operator & is used to evaluate the address of its operand.
The
indirection operator * is used to evaluate the value stored at the address
given by its operand. The operand must be of pointer type; ie, it can either be
an array (which is a self-referential pointer), a pointer to a variable (data
pointer) or a pointer to a function (function pointer).
Example
of a data pointer:
#include<stdio.h>
int main()
{
int val, a=10;
int *p; //declares a pointer variable
p=&a; //now p stores the address of a
val=*p; //now val stores the value of a
printf(" Address of a: %X", p);
printf("Value of a: %d",val);
return 0;
}
In
the above program the statement
int *p
declares an integer pointer (a pointer that stores the address of an integer
variable).
To
store the address of a in p, the address of operator is applied to a and
the result is stored in p as shown in the instruction
p=&a;
Now
p=&a;
Suppose
the address of a is 1004 i.e .
&a=1004
Since
p stores the address of a, then
p=&a
p=1004
Now
the value present at the address 1004 is the value stored in a which is
10(a=10).
To
access the value stored in a using the pointer variable
p
we need to apply the indirection operator *
on p. When the indirection
operator is applied on p (*p),
it reads the value stored at the address contained in p; ie,
the value stored at the address 1004; ie, the value of a.
The result of indirection is stored in the integer type variable val
as shown in the statement val =*p;.
The indirection operator is also called the value at operator as it gives the value stored at a particular address.
To
read the address stored in p, the format specifier
%X
is used in the printf statement as
addresses are generally in hexadecimal.
The
relationship between pointers and arrays has been discussed to some extent
while discussing the array subscript operator. Function pointers is an advanced
concept that will be discussed in a later article on pointers.
The
next article will continue with the unary operators and the other operators in
C.