C - Pointer Concepts and Addressing Mechanism in C

Pointer – Definition

A pointer is a variable that stores the memory address of another variable instead of storing a direct value.

Example:

int a = 10;
int *p = &a;

Here:

  • a stores value 10

  • p stores the address of a

Addressing Mechanism in C

The addressing mechanism refers to how C programs access memory locations using addresses and pointers.

C supports direct addressing and indirect addressing.

Direct Addressing

  • Variable is accessed directly by its name

  • Uses the actual memory location internally

Example:

int a = 5;
printf("%d", a);

Indirect Addressing

  • Variable is accessed through its address using pointers

  • Uses dereferencing operator (*)

Example:

int a = 5;
int *p = &a;
printf("%d", *p);

Here:

  • &a → address of a

  • *p → value stored at that address

Pointer Operators

1. Address-of Operator (&)

  • Returns the address of a variable

Example:

int a = 10;
printf("%p", &a);

2. Dereference Operator (*)

  • Accesses the value stored at an address

Example:

int *p;
*p = 20;

Types of Pointers

1. Integer Pointer

int *p;

2. Pointer to Pointer

  • Stores address of another pointer

Example:

int **pp;

3. Null Pointer

  • Points to nothing

  • Prevents accidental access

Example:

int *p = NULL;

4. Void Pointer

  • Can point to any data type

  • Must be type-cast before dereferencing

Example:

void *p;

5. Dangling Pointer

  • Points to memory that has been freed

Example:

free(p);   // p becomes dangling

Pointer Arithmetic

Pointer arithmetic depends on the data type size.

Example:

int *p;
p = p + 1;   // moves by sizeof(int)

Relationship Between Arrays and Pointers

  • Array name stores base address

  • Pointer can access array elements

Example:

int a[3] = {10, 20, 30};
int *p = a;

Access:

*(p + 1) = 20;

Advantages of Pointers

  • Efficient memory access

  • Used in dynamic memory allocation

  • Essential for data structures

  • Enables function call by reference

Disadvantages of Pointers

  • Complex to understand

  • Can cause memory leaks

  • Risk of dangling and wild pointers