Question

I ran into some code I couldn’t find an answer to on Google or SO. I am looking at a thread function which returns void* as you could expect. However, before the thread function ends it suddenly pulls this stunt,

return (void*) 0;

What is the purpose of that? I can’t make any sense of it.

edit:

After understanding this is the same as NULL– it is my thought they used this to skip including stdlib.

Answer 1

(void*)0 is the null pointer, a.k.a. NULL (which actually is a macro defined in several header files, e.g. stddef.h or stdio.h, that basically amounts to the same thing as (void*)0).

Update:

How to explain null pointers and their usefulness? Basically, it’s a special value that says, “This pointer doesn’t point anywhere,” or, “This pointer is not set to a valid object reference.”

Historical note: Tony Hoare, who is said to have invented null references in 1965, is known to regret that invention and thus calls it his “Billion Dollar Mistake”:

Whenever you work with pointers, you must make sure to never dereference a null pointer (because it doesn’t reference anything by definition). If you do it anyway, you’ll either get abnormal program termination, a general protection fault, or unexpected program behaviour at the very least.