C Foundation

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Basic IO's

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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

Looping

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Functions

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Scope

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Storage Classes

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Array

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String

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Pointer

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Structure

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What is Union

Files

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

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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

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

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

Note:

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

null-vs-uninitialized.c
#include <stdio.h>
int main()
{
int *nptr = NULL, *ptr;
if(nptr == 0)
  printf(" *nptr is a Null pointer \n ");
else
  printf(" *nptr is a not a Null pointer \n ");
if(ptr == 0)
  printf(" *ptr is a Null pointer \n ");
else
  printf(" *ptr is a not a Null pointer \n ");
return 0;
}
  • *nptr is a Null pointer
  • *ptr is a not a Null pointer

Note:

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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