C++ Null Pointers with examples

In this tutorial, we will learn about null pointers in C++ and see various uses of null pointers with some examples. I will try to make this tutorial easy to understand. Let’s get started.

Null Pointers in C++

A NULL pointer is a special type of pointer that does not point to any memory location. In other words, we can say that a pointer represents an invalid location. Whenever a value is assigned as  NULL to a pointer, then that pointer is considered as a NULL pointer. NULL is itself a special type of pointer. When we initialize a pointer with NULL then that pointer also becomes a NULL pointer.

Example to understand what is a NULL pointer.

#include <iostream>

using namespace std;
int main(){
 int *ptr = NULL; // This is a NULL pointer 
 return 0; 
}

 

Let’s see some uses of NULL pointer:

1. It is used to initialize a pointer when that pointer isn’t assigned any valid memory address yet. That is it’s a good practice to assign a pointer with null if a not valid address is defined.
2. It is also useful in handling errors when using the malloc function. Sometimes malloc returns null when memory is not allocated. In that case, we can use NULL for handling errors.

   #include <iostream> 
   using namespace std; 
   int main(){ 
       int *ptr; 
       ptr = (int*)malloc(sizeof(int)); 
       if(ptr == NULL)
          cout<<"Memory could not be allocated"<<endl; 
       else 
          cout<<"Memory allocated successfully"<<endl; 
          return 0; 
       
   }

   OUTPUT:
   Memory allocated successfully

   It is good practice to initialize a pointer as NULL.
   It is a good practice to perform a NULL check before dereferencing any pointer to avoid surprises.

To check pointer is null or not.

#include <iostream>
using namespace std;
int main()
{
    int a = 5;
    int *ptr = &a;
 
    if(ptr != nullptr)
    {
        cout <<  "It is not NULL Pointer" << endl ;
    }
    else
    {
        cout << "It is a NULL Pointer" << endl;
    }
    return 0;
}

OUTPUT:

It is not a NULL POINTER.

Hope you liked this tutorial. Happy Learning !!

Also Read: How to set a pointer to null in C++