is this a g++ bug or an obscure ISO rule?

[Josh Fryman]

if i use the code as follows, everything is fine.  if i replace the 
"int x" with "void * x" (and cast appropriately), i get compiler 
errors.  i don't see in Stroustrup, 3rd ed, where this is an error 
with "void *".

what am i missing?  this is g++ 3.1.1 on sun-sparc-solaris2.8.

  void
  foo::foo_method( void )
  {
     int x;
     void (foo::*ptr)(void) = &foo::foo_method;

     x = (int)(this->*ptr);

     cout << "foo::foo_method lives at addr " << (int*)x << endl;
  }

thanks,

josh fryman