Pointers

Definition

Pointer is a variable which stores the address of another variable. Since pointer is also a kind of variable, thus pointer itself will be stored at different memory location

Declaration

data_type  *pointer_name;

Data type represents Type of variable that the pointer points to,

Asterisk is called as Indirection Operator

Initialization

Pointer variable holds address of another variable

data_type variable;
data_type *pointer;
pointer = &variable;

Memory required for storing pointer

1. Pointer Variable Stores the address of the variable
2. Variable may be integer,character,float but the address of the variable is always integer so Pointer requires 2 bytes of memory

Pointer operators

• Referencing
• Dereferencing

Referencing

• A pointer variable is made to refer to an object. The reference to an object can be created with the help of a reference operator &
• The reference operator & is a unary operator and should appear on the left side of the operand
• The operand of reference operator should be a variable of arithmetic type or pointer type or function type
• The reference operator is also known as address of operator

Dereferencing

• Dereferencing Operation is performed to access or manipulate data contained in memory location pointed to by a pointer
• The object pointed to or referenced by a pointer can be indirectly accessed by dereferencing the pointer
• A dereferencing operation allows a pointer to be followed to the data object to which it points
• A pointer can be dereferencing using a dereference operator (*)
• The dereference operator & is a unary operator and should appear on the left side of the operand
• The operand of a dereference operator should be of pointer type
• The dereference operator is also known as indirection operator or value-at operator

#include<stdio.h>
int main()
{
	int a = 3;
	int *ptr = &a;
	int **pptr = &ptr;
	printf("a=%d\n",a);
	printf("&a = %p\n",&a);
	printf("ptr=%p\n",ptr);
	printf("*ptr = %d\n",*ptr);
	printf("&ptr = %d\n",&ptr);
	printf("pptr=%p\n",pptr);
	printf("**pptr = %d\n",**pptr);
	printf("&pptr = %d\n",&pptr);
	return 0;
}

Output

a=3
&a = 000000000062FE1C
ptr=000000000062FE1C
*ptr = 3
&ptr = 6487568
pptr=000000000062FE10
**pptr = 3
&pptr = 6487560

Assigning to a pointer

• A pointer can be assigned or initialized with the address of the object. A pointer object cannot hold a non-address value and thus can only be assigned or initialized with address
• A pointer to a type cannot be initialized or assigned the address of an object of another type
• A pointer can be assigned or initialized with another pointer of the same type. However, it is not possible to assign a pointer of one type to a pointer of another type without explicit type casting

Generic pointer (void pointer)

• In C General Purpose Pointer is called as void Pointer.
• It does not have any data type associated with it
• It can store address of any type of variable
• The compiler has no idea what type of object a void Pointer really points to 

Syntax

void * pointer_name;

Example

void *ptr;    // ptr is declared as Void pointer
char cnum;
int inum;
float fnum;
ptr = &cnum;  // ptr has address of character data
ptr = &inum;  // ptr has address of integer data
ptr = &fnum;  // ptr has address of float data

Advantage

To increase reusability of pointer.

Null pointer

• A null pointer is a special pointer that does not point anywhere.
• It does not hold the address of any object or function
• It has numeric value 0

Syntax

int *nptr = 0;

The macro or symbolic constant NULL defined in the header files stdio.h, stddef.h, stdlib.h, alloc.h and mem.h can be used for the creation of a null pointer

Example

int *iptr = NULL;

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