Question

For example, I have 2 classes as defined in following order…

class A
{
     int value;

     printValue(B b)
     {
        cout << b.value
     }
};

class B  
{
   int value;

   printValue(A a)
   {
      cout << a.value;
   }

}

How can I use the B object in A, as B definition is below ?

Answer 1

You can separate declaration and implementation of the classes, forward declare them in the declaration header files, and use references in the functions.

file A.h

class B; // forward declaration
class A {
  public:
     int value;
     void printValue(const B& b) const; // pass by reference
};

file B.h

class A; // forward declaration
class B  {
  public:
   int value;
   void printValue(const A& a) const; // pass by reference
};

Then, have separate implementation files. For example, A‘s implementation file A.cpp:

#include "A.h"
#include "B.h"

void A::printValue(const B& b) const {
   std::cout << b.value;
}

and similarly for B.cpp.

Note that I have fixed the missing return types for the printValue functions, and made those functions const.