Behaviour of a static member in static function

[KarlisRepsons]

When you look at the following code, you'll see, there is a static member, which is initialised to be 0, nevertheless, such initialization happens just once for all calls!

#include <iostream>

using namespace std;

class A
{
public:
   static A *getA()
   {
      static A *a = 0;
      if (!a)
      {
         a = new A;
         cout << "made new \"A\"!" << endl;
      }
      return a;
   }
};

int main(int argc, char **args)
{
   A *a = A::getA();
   a->getA();
   A::getA();
   return 0;
}

Which produces an output like this:

entered function.
made new "A"!
entered function.
entered function.

So my question is: how can that be explained and how can one be sure to use this kind of static member's nature, perhaps in some other cases too?

[kbw]

Static variables have global lifetime, local scope and are initialised on first use. They are given a default value of zero.