C Foundation

What is C? C Compiler Installation C Extensions C Compiler C Interpreter C Program Structure

C Basics

C Keywords C Data Types C Identifiers C Variables C Constant C Escape Sequences C Constant and Volatile C Typecast


What is Operator C Comma Operator C Arithmetic Operators C Relational Operators C Logical Operators C Bitwise Operators C Conditional Operators C : : Operator C Operator Priority

Basic IO's

Basic IO's C Formatted Functions C Unformatted Functions C Common Functions

Control Statements

What is Control Statement C if Statement C if else Statement C Nested if Statement C Else if Statement C Break Statement C Continue Statement C Switch Statement C Goto Statement


What is Control Loop C for Loop C Nested for Loop C while Loop C Nested while Loop C do while Loop C Nested do while loop


What is Function C User Defined Functions C Recursion C Passing Parameters


Scope C Local Scope C Global Scope

Storage Classes

What is Storage Class C Auto C Extern C Static C Register


What is Array C One Dimensional Array C Two Dimensional Array C Multi Dimensional Array C Arrays Of Strings


What is String C String Functions


What is Pointer C Pointers Arithmetic C Pointer to Pointer C Pointers and Arrays C Pointers and Strings C Pointer to Functions Void Pointers Null Pointers C Null and Void Pointer


What is Structure C Struct within Struct C Array within Structure C Pointer to Structure C Structure and Function C Enum C Bitfield Structure C Type def


What is Union


What is File C read a file C write a file C File Handling C Error Handling C Low Level Disk I/O C Other file functions

Memory Allocation

What is Memory Allocation C Malloc() C Calloc() C Free() C Realloc() C Coreleft()

C Reference

All ASCII Code Basic C Questions

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The ones who are crazy enough to think they can change the world are the ones who do.
- Steve Jobs

C Null Pointer

What Is Null Pointer?

C program defines the states that for each pointer type, When a pointer variable is declared and initialized either by a Null value or by 0 explicitly then the pointer variable is said to be null pointer. Conceptually a null pointer is a pointer that points nowhere, it doesn't have an address of any function or a variable , instead pointer is initialized with zero or null to indicate that this pointer variable is still unused.

null pointer in c

Syntax - Null Pointer

data type *variablename = NULL;

Void Pointer Dereferencing

Dereferencing pointer variable of void type is bit complex than usual pointer variable. Consider the following program which will not compile .

C Program - Null Pointer

#include <stdio.h>
int main()
int *iptr = NULL;
printf("\nValue of iptr = %u", iptr);
return 0;
  • Value of iptr = 0


The above program shows that the pointer variable is initialized by a NULL value.

Null Pointer vs Unintitialized Pointer

Being a programmer, in most cases we will uninitialize a pointer variable instead of initializing a Null value to it. Conceptually the null pointer is highly different from uninitialized pointer variable because null pointer points nothing whereas uninitialized pointer points to some garbage address.

C Program - Null Pointer vs Unintitialized Pointer

#include <stdio.h>
int main()
int *nptr = NULL, *ptr;
if(nptr == 0)
  printf(" *nptr is a Null pointer \n ");
  printf(" *nptr is a not a Null pointer \n ");
if(ptr == 0)
  printf(" *ptr is a Null pointer \n ");
  printf(" *ptr is a not a Null pointer \n ");
return 0;
  • *nptr is a Null pointer
  • *ptr is a not a Null pointer


In the above program, we declared two pointer variable *nptr and *ptr of integer datatype. *nptr is initialized to zero i.e) Null pointer and *ptr is uninitialized pointer variable. This program clearly states that uninitialized pointer is extremely different from null pointer.

Null Pointer Datatype

Null pointer doesn't belongs to any special datatypes. Datatypes such as char *, int *, float *, double *, long int*, void* are all can be a Null pointer.

What is Null?

Many programmers like you will not prefer to use a plain 0 to initialize the pointer variable to act as null pointer because 0 is of integer datatype and will scattered through their entire pograms, as 0 can represent either numbers or pointers. Therefore, to reduce the conflict, the C program introduces the null value, The NULL is the preprocessor macro which is defined in the #include<stdio.h> header files. Using null to initialize the null pointer is for stylistic convention only, the preprocessor will convert the null back into 0 at the time of compilation.

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