Question

I have the following code:

Master.h

#ifndef MASTER_H
#define MASTER_H

class Master
{
   friend class Friend;

   public:
      Master(void);
      ~Master(void);
      void CallFriendFunction(int largeData);

   private:
      int    largeData;

      //Want this class to share largeData;
      Friend testFriend;
};
#endif // MASTER_H

Master.cpp

#include "Master.h"

Master::Master(void)
{
   //Inentionally left blank
}

Master::~Master(void)
{
   //Intentionally left blank
}

void Master::CallFriendFunction(int largeData)
{
   this->largeData = largeData;
   this->testFriend.Test(this);
}

Friend.h

#ifndef FRIEND_H
#define FRIEND_H

#include "Master.h"

class Friend
{
   public:
      Friend(void);
      ~Friend(void);

      void Test(Master* masterPtr);
};

#endif // FRIEND_H

Friend.cpp

#include "Friend.h"
#include <iostream>

Friend::Friend(void)
{
   //Intentionally left blank
}

Friend::~Friend(void)
{
   //Intentionally left blank
}

void Friend::Test(Master* masterPtr)
{
   std::cout << masterPtr->largeData << std::endl;
}

I want class Friend to be able to share Master’s private members. However, I can’t get this code to compile. I’ve tried Forward Declaration, and #includes, but I start getting into circular dependencies. When Friend class is not a member of Master class, the code compiles?

Is it possible for Friend class be a member of Master and be friends?
How else can Friend class have access to Masters private members?

Answer 1

You need the following includes and forward declarations:

In Master.h:

#include "Friend.h"

In Friend.h:

class Master;

In Friend.cpp:

#include "Master.h"

Putting the forward declaration in Friend.h prevents circular dependency. A forward declaration is enough there because you only declare a Master* parameter, without using its members yet.

You do need to include Friend.h from Master.h because you are declaring a Friend member, and this requires a complete type.