C Programming language

# NULL Pointer

A pointer that is assigned NULL is called a null pointer. In that case no need to assigned to the exact address. This is done at the time of variable declaration. If a pointer contains the null (zero) value, it is assumed to point to nothing.

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

#include <stdio.h>

void main ()
{
   int  *ptr = NULL;

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

Note: On most of the operating systems, programs are not permitted to access memory at address 0 because that memory is reserved by the operating system.

To check for a null pointer you can use an if statement as follows:

if(ptr)     /* succeeds if p is not null */
if(!ptr)    /* succeeds if p is null */