Null pointer is a special reserved value of a pointer. A pointer of any type has such a reserved value. Formally, each specific pointer type (int *, char * etc.) has its own dedicated null-pointer value. Conceptually, when a pointer has that null value it is not pointing anywhere.

Void pointer is a specific pointer type - void * - a pointer that points to some data location in storage, which doesn't have any specific type.

So, once again, null pointer is a value, while void pointer is a type. These concepts are totally different and non-comparable. That essentially means that your question, as stated, is not exactly valid. It is like asking, for example, "What is the difference between a triangle and a car?".

The two concepts are orthogonal:

1. A void pointer, (void *) is a raw pointer to some memory location.
2. A null pointer is a special pointer that doesn't point to anything, by definition. It can be a pointer to any type, void or otherwise.

A void pointer can be null or not:

void *void_ptr1 = nullptr;
void *void_ptr2 = malloc(42);
void *void_ptr3 = new Foo;               // void * can point to almost anything
void *void_ptr4 = (char*)void_ptr3 + 1;  // even somewhere inside an object

A non-void pointer can also be null or not:

Foo *f = nullptr;
Foo *g = new Foo;