C++ - 2 classes 1 file

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))

---

Thanks, all 5 of you. Who exactly am I supposed to mark as accepted? :)

From stackoverflow

• put at the first line:

  class B;
  

  Yuval A : You were first, thanks! :)

• 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

• 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.

  Evan Teran : good answer, so you get the +1. But for reference the term is "forward declaration"

• Yes. You need a forward declaration:

  class B; // add this line before A's declaration
  
  class A {
      public:
          void doSomething(B *b) {};
  };
  
  class B {
      public:
          void doSomething(A *a) {};
  };
  

• You can try a forward declaration like

  class B;
  class A {
    void Method( B* );
  };
  class B{
  };
  

  but you will only be able to declare pointer and reference variables for B then. If you want more (like a method that dereferences B* variable) you can provide a declaration only and define methods later in the same file - at the point where both classes declaration is already available.

• You need to forward declare B.

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

  (And BTW, you don't need the semi-colons after the member function curly braces. :) )

• The C++ FAQ Lite answers this question and others. I'd seriously considering reading that thing end to end, or getting the book and doing the same.

  ssg : +1 for saying something different than the bunch

• Add another declaration of B before A:

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