Question

What is the usage of the NULL pointer in C?

Answer 1

There is a lot of usage of the null pointers in C but here I am mentioning some important usage of the null pointer in C which you must know.

• A pointer that is not pointing the address of a valid object or valid memory should be initialized to NULL. It prevents the pointer to become a dangling pointer and ensure the programmer that pointer is not pointing anywhere.

char *pcData = NULL; //Prevent to become dangling pointer

• A very good habit to check the validity of the pointers before using it. It prevents the crashing of the code and unwanted result. The null pointer helps you in error handling.

#include<stdio.h>

#include<stdlib.h>

int main()

{

int *piData = NULL;

piData = malloc(sizeof(int)*10);

if(NULL == piData)

{

//exit

}

else

{

//code

free(piData); //free after the use

}

return 0;

}

• There is a lot of library function in C where pointer arguments are optional. So passing the null pointer to a function argument is useful when you don’t want to pass any valid memory or object address.

For example,

int pthread_create(pthread_t *thread, const pthread_attr_t *attr,

void *(*start_routine) (void *), void *arg);

• As a summary, you can understand that a null pointer can be used as an error value, a sentinel value or to terminate indirection in the recursive data structure.