Declare an object even before that class is created

Question

Is there anyway to declare an object of a class before the class is created in C++? I ask because I am trying to use two classes, the first needs to have an instance of the sec

Answer 1

You can't do something like this:

class A {
    B b;
};
class B {
    A a;
};

The most obvious problem is the compiler doesn't know how to large it needs to make class A, because the size of B depends on the size of A!

You can, however, do this:

class B; // this is a "forward declaration"
class A {
    B *b;
};
class B {
    A a;
};

Declaring class B as a forward declaration allows you to use pointers (and references) to that class without yet having the whole class definition.