What's the difference between void* and void**?

Question

It\'s the special property that void* can also be assigned a pointer to a pointer and cast back and the original value is received.

I read this line

Answer 1

if you want to store some pointer or anything you will probably use void*.

However if you want to write a function which can be able to initialize this magic pointer, then you need pass this argument to this function as void**

void   fun1();
int    fun2(int);
double fun3(long);
bool   fun4(int, long, double);


int rand(void** pp)
{
  switch(time()%4)
  {
    case 0: *pp = fun1; return 0;
    case 1: *pp = fun2; return 1;
    case 2: *pp = fun3; return 2;
    case 3: *pp = fun4; return 3;
  }
}

int main()
{
    void* pointer;
    int funId;

    funId = rand(&pointer);

    setCallback(pointer, funId);
}