Differentiate the NULL pointer with Void pointer in C language

In C programming, NULL pointers and void pointers are two distinct concepts that serve different purposes. A NULL pointer represents a pointer that doesn't point to any valid memory location, while a void pointer is a generic pointer type that can point to any data type but requires type casting for dereferencing.

Syntax

/* NULL Pointer */
data_type *pointer_name = NULL;

/* Void Pointer */
void *pointer_name;

NULL Pointer

A NULL pointer is a pointer that doesn't point to any valid memory location. It's used to indicate that the pointer is not currently pointing to any object. NULL is typically defined as 0 or ((void*)0) in C.

Example

Here's a demonstration of NULL pointer usage −

#include <stdio.h>
#include <stdlib.h>

int main() {
    int *ptr = NULL;  // NULL pointer initialization
    
    printf("NULL pointer value: %p<br>", (void*)ptr);
    
    // Check if pointer is NULL before using
    if (ptr == NULL) {
        printf("Pointer is NULL - safe to check!<br>");
    }
    
    // Allocate memory
    ptr = (int*)malloc(sizeof(int));
    *ptr = 25;
    
    printf("After allocation: %d<br>", *ptr);
    
    free(ptr);
    ptr = NULL;  // Good practice: set to NULL after freeing
    
    return 0;
}

NULL pointer value: (nil)
Pointer is NULL - safe to check!
After allocation: 25

Void Pointer

A void pointer is a generic pointer that can point to any data type. It cannot be dereferenced directly and must be cast to the appropriate pointer type before use.

Example

Here's how void pointers work with different data types −

#include <stdio.h>

int main() {
    int num = 42;
    float price = 99.99;
    char grade = 'A';
    
    void *vptr;  // void pointer declaration
    
    // Point to integer
    vptr = &num;
    printf("Integer value: %d<br>", *(int*)vptr);
    
    // Point to float
    vptr = &price;
    printf("Float value: %.2f<br>", *(float*)vptr);
    
    // Point to character
    vptr = &grade;
    printf("Character value: %c<br>", *(char*)vptr);
    
    return 0;
}

Integer value: 42
Float value: 99.99
Character value: A

Key Differences

Conclusion

NULL pointers are used for safety and initialization, ensuring pointers don't point to invalid memory. Void pointers provide flexibility for generic programming by allowing a single pointer to work with multiple data types through proper casting.