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 second class within it, but the second class also contains an instance of the first class. I realize that you may think I might get into an infinite loop, but I actually need to create and instance of the second class before the first class.

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.