Recursive Includes

Hello, I'm trying to implement a sort of callback object, but having some trouble with a recursive include problem, to demonstrate:

Code:

---

#ifndef TEST1_HPP_
#define TEST1_HPP_

#include "test2.hpp"

class A {
        B *b;
       
        public:
                A(B *obj) {
                        b = obj;
                }
               
                void func() {
                        b->print();
                }
};

#endif /*TEST1_HPP_*/

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Code:

---

#ifndef TEST2_HPP_
#define TEST2_HPP_

#include "test1.hpp"

class B {
        private:
                A a;
       
        public:
                B() : a(this) {}
               
                void test() {
                        a.func();
                }
               
                void print() {
                        std::cout << "Hello World!" << std::endl;
                }
};

#endif /*TEST2_HPP_*/

---

Code:

---

#include "test1.hpp"

int main() {

        return 0;
}

---

EDIT: The errors in question are:

Code:

---

In file included from test2.hpp:4,
                from test.cpp:3:
test1.hpp:7: error: ISO C++ forbids declaration of ‘B’ with no type
test1.hpp:7: error: expected ‘;’ before ‘*’ token
test1.hpp:10: error: expected `)' before ‘*’ token
test1.hpp: In member function ‘void A::func()’:
test1.hpp:15: error: ‘b’ was not declared in this scope
In file included from test.cpp:3:
test2.hpp: In constructor ‘B::B()’:
test2.hpp:11: error: no matching function for call to ‘A::A(B* const)’
test1.hpp:6: note: candidates are: A::A()
test1.hpp:6: note:                A::A(const A&)

---

The obvious question is, what am I doing wrong in trying to get this to work?

Don't know what IDE you're using, but you should be able to get the output of just the pre-processor (before compilation even starts). You'll see that one of your classes is defined before the other, so calling B in the class A definition won't work, since B hasn't happened yet.

I think you'll need a forward declaration (like "class B;") so that the name B is recognized as a type.

The definition of class A doesn't need the definition of class B. Therefore, don't include test2.hpp, but instead just declare the class:

Code:

---

class B;

class A { ... };

---

However, the definitions of A's members do need the definition of B, so separate them out into the implementing source file.

Code:

---

#include "test1.hpp"
#include "test2.hpp"

void A::func()
{
  b->print();
}

---

Cheers!