C / C++ / MFC

//xxx.h
class xxx {
	public:
		static int ddd;
	//other stuff
};

//xxx.cpp
int xxx::ddd = 0; //you should provide an initial value, but it isn't required

class xxx {
protected:
	int x;
	int y;
private:
public:
	int ddd;
	class ccc {
	protected:
	private:
		xxx *m_pParent;
	public:
		int sad() {
			printf("%d\r\n", m_pParent->ddd);
			//the \r character is redundant in a console (although needed if the console is piped to a file or text box)
		}
		ccc(xxx *pParent) : m_pParent(pParent) {}
		~ccc(){}
	};
	xxx() {
		ddd = 0;
		x = 10;
		y = 11;
	}
	~xxx() {
		x = 0;
		y = 0;
	}
};

// Parent.h
class Parent {
private:
   int sum;
   Parent() : sum(0) {} // private constructor prevents accidental creation of additional parents
   Parent(const Parent&) {} // same for copy constructor
   Parent& operator=(const Parent&) {} // same for assignment
public:
   static Parent* get();
   void work(const class Child& child); // use forward declaration for (yet) undefined class Child
   int sum() const { return sum; } // get some results
};

// Child.h
class Child {
private:
   int x; // some data
public:
   Child(int a);
   int value() const { return x; }
};

// Parent.cpp
#include "Parent.h"
#include "Child.h"
static Parent* theParent = 0;
Parent* Parent::get() {
   if (theParent==0)
      theParent = new Parent;
   return theParent;
}
Parent::work(const Child& child) {
   // do something
   sum += child.value();
}

// Child.cpp
#include "Child.h"
#include "Parent.h"

Child::Child(int a) : x(a) {
   Parent* parent = Parent::get();
   parent->work(*this);
}

// main.cpp
#include "Child.h"
#include "Parent.h"

void test() {
   Child abe(3), bert(4), chris(5);
   printf("sum=%d\r\n", Parent::get()->sum()}; // prints "sum=12"
}