Pointers and circular dependencies

Question

I am trying to get into C++ and I encountered few issues. My two classes look like that:

#include "Account.h"

class Program
{
public:
    Program(void);
    ~Program(void);
    void SetAccount(Account account);
};

#include "Program.h"

class Account
{
public:
    Program *program;
    Account(void);
    ~Account(void);
};

By passing an instance of the Account class to SetAccount function am I making a copy of it or I am passing it as a reference? As I understand I am making a copy of it, but I wanted to be sure. To pass it as a reference I need to use pointers, right?

Another issue I encountered is with my Account class. Lets say it needs to have Program class reference at some point. The problem is that both Program and Account classes have lines "#include" to each other so it causes circular dependency. Any ideas how to solve it?

Edited

My classes now looks like that:

#include "Account.h"

class Program
{
public:
    Program();
    ~Program();
    void SetAccount(Account account);
};

class Program;

class Account
{
public:
    Program *program;
    Account();
    ~Account();
};

When I try to initialize *program in Account constructor I get "incomplete type is not allowed" and "'Program' : no appropriate default constructor available".

Answer 1

In your definition of

void SetAccount(Account account);

the class Account must be known at compiletime, so you have to include the definition before it.

In your account class you are using only a pointer, so you can make a forward declaration

class Program;
class Account
{
public:
    Program *program;
   ...
};

This is just to tell the compiler that a definition of an object named Program exists, but the size of the object is not necessarily known. As long as only a pointer is required, that is enough. If you want to dereference such a pointer you have to provide the class definition then.