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pointer is known as derived data type. It is derived from built in data types.
A pointer variable always contains the address of another variable in it. The address represents memory location of computer memory.
A pointer allows us to access and manipulate memory addresses.

Following are the features of pointer:

  • Pointer allows Dynamic Memory management facility to the C Programmer.
  • Pointer increases the execution speed of the program.
  • Pointer Save memory space.
  • Pointer allows programmer to directly access and manipulate memory addresses. So it is widely used to represent dynamic data structure such as stack, queue, linked list, tree etc…
  • Pointer allows programmer to pass address of the original variable to the function, so function can works with original variable inside function instead of dummy variables (Call by Reference).
  • Array and string, can be effectively handled using pointers.
  • Pointers are also used for file handling.

Use of Pointer

There are a few important operations, which we will do with the help of pointers very frequently. (a) We define a pointer variable, (b) assign the address of a variable to a pointer and (c) finally access the value at the address available in the pointer variable. This is done by using unary operator * that returns the value of the variable located at the address specified by its operand. The following example makes use of these operations −

#include <stdio.h>

int main () {

   int  var = 20;   /* actual variable declaration */
   int  *ip;        /* pointer variable declaration */

   ip = &var;  /* store address of var in pointer variable*/

   printf("Address of var variable: %x\n", &var  );

   /* address stored in pointer variable */
   printf("Address stored in ip variable: %x\n", ip );

   /* access the value using the pointer */
   printf("Value of *ip variable: %d\n", *ip );

   return 0;
Output :
Address of var variable: bffd8b3c
Address stored in ip variable: bffd8b3c
Value of *ip variable: 20

NULL Pointers

It is always a good practice to assign a NULL value to a pointer variable in case you do not have an exact address to be assigned. This is done at the time of variable declaration. A pointer that is assigned NULL is called a null pointer.

The NULL pointer is a constant with a value of zero defined in several standard libraries. Consider the following program −

#include <stdio.h>

int main () {

   int  *ptr = NULL;

   printf("The value of ptr is : %x\n", ptr  );
   return 0;
Output :
The value of ptr is 0

In most of the operating systems, programs are not permitted to access memory at address 0 because that memory is reserved by the operating system. However, the memory address 0 has special significance; it signals that the pointer is not intended to point to an accessible memory location. But by convention, if a pointer contains the null (zero) value, it is assumed to point to nothing.

Pointers in Detail

Pointers have many but easy concepts and they are very important to C programming. The following important pointer concepts should be clear to any C programmer −

Sr.No. Concept & Description
1 Pointer arithmetic

There are four arithmetic operators that can be used in pointers: ++, --, +, -

2 Array of pointers

You can define arrays to hold a number of pointers.

3 Pointer to pointer

C allows you to have pointer on a pointer and so on.

4 Passing pointers to functions in C

Passing an argument by reference or by address enable the passed argument to be changed in the calling function by the called function.

5 Return pointer from functions in C

C allows a function to return a pointer to the local variable, static variable, and dynamically allocated memory as well.

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