Ciclic class use inside another class - c++

Question

I have two classes inside one cpp file like this:
class A
{
private:
int somethingPrivate;
B *aReferenceToB;
public
B returnSomeB()
{
aReferenceToB->someFunction();
return *aReferenceToB;
}
};
class B
{
private:
A needed_Class_A_var;
public:
void someFunction()
{
return;
}
};
This ciclic use of these two classes, one inside another, generates all sort of errors like
error C2143: syntax error : missing ';' before '*'
How can I resolve this ciclic include problem without creating separate files for each class and using only one cpp file?
I have tried to add a class B; declaration before class A definition wich does not work properly.

Answer 1

Before you access members of the B class (aReferenceToB->someFunction()), or even try to return the object of B (not the pointer to B) (B returnSomeB), you need to have a complete definition of class B first.
So, just extract the returnSomeB body out of the class A definition, and put it in place where the full definition of B is known.
class B;
class A
{
private:
int somethingPrivate;
B *aReferenceToB;
public:
B returnSomeB();
};
class B
{
private:
A needed_Class_A_var;
public:
void someFunction()
{
return;
}
};
B A::returnSomeB(){
aReferenceToB->someFunction();
return *aReferenceToB;
}
Please note that if you try to write something like this:
class B;
class A
{
private:
int somethingPrivate;
B *aReferenceToB;
public:
B* returnSomeB() { return aReferenceToB; }
};
that would be valid, because you're only manipulating with the pointers here (in this case, you're not creating object of B, and you don't access any of B's members), and the size of the pointer is known at the compile time, even without class B definition.