What is an `int foo::*bar::*`?

Here’s a “valid” way of initializing such a monstrosity:

struct bar;

struct foo
{
    int y;    
    int bar::* whatever;
};

struct bar
{
    foo aFoo;
};

int bar::* foo::* ptr = &foo::whatever;

As we can see, ptr is a pointer to a member of foo (foo::*, reading right to left), where that member is itself a pointer to a member of bar (bar::*), where that member is an int.

How would I use an int bar::* foo::*

You wouldn’t, hopefully! But if you are under duress, try this!

struct bar
{
    foo aFoo;

    int really;
};

int bar::* foo::* ptr = &foo::whatever;
foo fleh;
fleh.whatever = &bar::really;
bar blah;
blah.*(fleh.*ptr) = 42;
std::cout << blah.really << std::endl;