infinite loop of headerfile problem

#include"B_wnd.h"
class A_wnd{
int xy;
B_wnd b_obj;
};

#include"A_wnd.h"
class B_wnd{
int bx;
A_wnd a_obj;
};

First of all why do you need a circular reference? Any real need or you want just to test?

First of all the headers will have circular reference. You can use a include guard to over come that. Mostly all advanced C/C++ processors can avoid it, but always when you include headers use include guards. In Microsoft VCC then I think you can use

#pragma once

After you overcome this you have a second problem.

Suppose you create an object of type A_wnd.
When the constructor of A_wndis called it calls the constructors of B_wnd. Inside this again constructor of A_wnd will be called. This is a recursive problem. You will go out of stack and there will be crash.

You can use pointers or reference instead of real objects.

Use this:

//A_wnd.h
#ifndef A_H
#define A_H
#include "B_wnd.h"

class B_wnd;

class A_wnd
{
    public:
	B_wnd* m_b;
};

#endif

//B_wnd.h
#ifndef B_H
#define B_H

#include "A_wnd.h"
class A_wnd;

class B_wnd
{
	public:
	A_wnd* f;
};
#endif

2 important issues:
1. ifndef - to avoid redefinition
2. Forward definition (class B_wnd; for example).