Question

to create an instance of another class from a class even if the class I want to have an instance of is declared next of the class I am creating an instance from. Just like in C# and Java.

Thank you

Answer 1

Sure. You just need a forward declaration. Something like this works just fine:

#include <iostream>

class B;

class A {
public:
    void hello( B &b );
    void meow();
};

class B {
public:
    void hello( A &a );
    void woof();
};

void A::hello( B &b ) { b.woof(); }
void A::meow() { std::cout << "Meow!" << std::endl; }

void B::hello( A &a ) { a.meow(); }
void B::woof() { std::cout << "Woof!" << std::endl; }

int main() { A a; B b; a.hello( b ); b.hello( a ); return 0; }

The key here is that you can only use pointers or references to a class until it has been fully defined. So in the example I gave, the hello() method in A can be declared to take a reference to B, even though we haven’t defined B at the point. After the definition of B, however, the definition of the method A::hello() is free to use B as it pleases.