Thread: 2 way association

How do I implement a binary association between 2 classes?

Like this:

Code:

Class A
{
private:
  B *m_bRef;
public:
  A(void);
};

Code:

Class B
{
private:
  A *m_aRef;
public:
  B(void);
};

when A is in a.hpp and B is in b.hpp

I tried with: [ Compiles (VC++) but instantly crashes ]

Code:

#include <string>
#include <iostream>

namespace Test
{
	class B;
	class A
	{
		friend class B;
	public:
		B *m_bRef;
		int m_int;

	public:
		A(int _int);
		int getBInt(void);
	};

	class B
	{
		friend class A;
	public:
		A *m_aRef;
		int m_int;

	public:
		B(int _int);
		int getAInt(void);
	};
}

Test::A::getBInt(void)
{
	return this->m_bRef->m_int;
}
Test::B::getAInt(void)
{
	return this->m_aRef->m_int;
}
Test::A::A(int _int)
{
	this->m_int = _int;
}
Test::B::B(int _int)
{
	this->m_int = _int;
}

int main()
{
	Test::A a(25);
	Test::B b(100);

	std::cout << a.getBInt();
	std::cout << b.getAInt();

	std::cin.get();

	return 0;
}

like this ?

Code:

#include <string>
#include <iostream>

namespace Test
{
	class B;
	class A
	{
		friend class B;
	private:
		B *m_bRef;
		int m_int;

	public:
		A(int _int);
		int getBInt(void);
		void setB(B *_b);
	};

	class B
	{
		friend class A;
	private:
		A *m_aRef;
		int m_int;

	public:
		B(int _int);
		int getAInt(void);
		void setA(A *_a);
	};
}

Test::A::A(int _int)
{
	this->m_int = _int;
	this->m_bRef = 0;
}
Test::A::getBInt(void)
{
	return this->m_bRef->m_int;
}
void Test::A::setB(Test::B *_b)
{
	this->m_bRef = _b;
}

Test::B::B(int _int)
{
	this->m_int = _int;
	this->m_aRef = 0;
}
Test::B::getAInt(void)
{
	return this->m_aRef->m_int;
}
void Test::B::setA(Test::A *_a)
{
	this->m_aRef = _a;
}

using namespace Test;
int main()
{
	A *a = new A(25);
	B *b = new B(100);

	a->setB(b);
	b->setA(a);

	std::cout << a->getBInt() << std::endl;
	std::cout << b->getAInt() << std::endl;

	std::cin.get();

	return 0;
}

Output :
100\n25\n

the only problem i have with this is that I'm separating code into declaration and definition parts (.hpp & .cpp parts )

Can I do it all in one piece in any way ?

Can I do it all in one piece in any way ?

No, at least one of the classes must be separate, you can't use a pointer before it's defined which would be the case if you defined the class members in the declaration. For example:

Code:

struct bar; // forward declaration
struct foo
{
	bar* pBar;
	foo()
	{
		pBar->value = 10; // <------ERROR, can't use before definition(below)
	}
};

struct bar
{
	int value;
};

foo::foo()
{		
	pBar->value = 10; // <------OK, has been defined (above)
}

What are the Cons & Pros of having this OO Design ?

Anyone?