C++ - 2 classes 1 file

Question

Suppose I want something of this sort, in one .cpp source file:

class A {
    public:
        void doSomething(B *b) {};
};

class B {
    public:
        void doSomething(A *a) {};
};

Is there anyway of doing this without splitting it into two separate files, and without receiving a compiler error (syntax error on doSomething(B *b))

Answer 1

put at the first line:

class B;

Answer 2

If I remember well, you can 'pre-declare' your class B.

class B; // predeclaration of class B

class A
{
   public:
      void doSomething(B* b);
}

class B
{
    public
      void doSomething(A* a) {}
}

public void A::doSomething(B* b) {}

Then, your class 'A' knows that a class 'B' will exists, although it hasn't been really defined yet.

Forward declaration is indeed the correct term, as mentionned by Evan Teran in the comments.

Answer 3

forward declare one class before other with

class B;
or
class A;

But still you won't be able to implement

void doSomething(B *b)

using only forward declaration of B. So you have to put definition of doSomething below full class A declaration