Forward Decleration

B.cpp

#include "B.hpp"
#include "C.hpp"

B::B()
: m_c(nullptr)
{
}

B.hpp

#pragma once

class C;

class B
{
public:
    B();
private:
    C* m_c;
};

C.cpp

#include "C.hpp"
#include "D.hpp"

C::C()
: m_d(nullptr)
{	
}

C.hpp

#pragma once

class D;

class C
{
public:
	C();
private:
    D* m_d;
};

D.hpp

#pragma once

class D
{
  
};

main.cpp

#include "B.hpp"

int main()
{
    B b;
}