Mutually recursive classes

Solution 1:

1. Forward-declare the classes (you could get away with forward-declaring only one of them, but for good form do both).
2. Forward-declare the methods (ditto).

class Class1;
class Class2;

class Class1
{
  Class2* Class2_ptr;
public:
  void Class1_method();
};

class Class2
{
  Class1* Class1_ptr;
public:
  void Class2_method();
};

void Class1::Class1_method()
{
  //...
  (*Class2_ptr).Class2_method();
  //...
}

void Class2::Class2_method()
{
  //...
  (*Class1_ptr).Class1_method();
  //...
}

Solution 2:

Use forward declaration.

class Class2;

class Class1
{
  Class2* Class2_ptr;
};

class Class2 
{
  Class1* Class1_ptr;
}

Because the methods in Class1 will depend on the actual definition of Class2, method definitions must occur after the Class2 declaration, since you can't use methods from only a forward declaration.

On the other hand, this kind of tight coupling is usually indicative of bad design.