What's the difference between a null pointer and a void pointer?

Question

Whats the difference between a Null pointer & a Void pointer?

Answer 1

A null pointer points has the value NULL which is typically 0, but in any case a memory location which is invalid to dereference. A void pointer points at data of type void. The word "void" is not an indication that the data referenced by the pointer is invalid or that the pointer has been nullified.

Answer 2

They are two different concepts: "void pointer" is a type (void *). "null pointer" is a pointer that has a value of zero (NULL). Example:

void *pointer = NULL;

That's a NULL void pointer.

Answer 3

Usually a null pointer (which can be of any type, including a void pointer !) points to:

• the address 0, against which most CPU instructions sets can do a very fast compare-and-branch (to check for uninitialized or invalid pointers, for instance) with optimal code size/performance for the ISA.

• an address that's illegal for user code to access (such as 0x00000000 in many cases), so that if a code actually tries to access data at or near this address, the OS or debugger can easily stop or trap a program with this bug.

A void pointer is usually a method of cheating or turning-off compiler type checking, for instance if you want to return a pointer to one type, or an unknown type, to use as another type. For instance malloc() returns a void pointer to a type-less chunk of memory, the type of which you can cast to later use as a pointer to bytes, short ints, double floats, typePotato's, or whatever.

Answer 4

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?".

Answer 5

Void refers to the type. Basically the type of data that it points to is unknown.

Null refers to the value. It's essentially a pointer to nothing, and is invalid to use.