Having two classes reference each other.

Hello! I'm new to the forums and C++ as well. I've been following through a few books but I haven't found how to do this correctly yet.

I'm programming a console application using Visual C++.

What I am aiming to do is to allow one class to reference another. This is for a game that me and couple of friends are programming.

I found a thread similar to this before I joined. However following through it I haven't produced any reliable results. So, here is my code, split up into 5 files.

The code compiles fine. However, in the linking stage, I recieve several errors:

Code:

---

Linking...
a.obj : error LNK2005: "public: __thiscall A::A(void)" (??0A@@QAE@XZ) already defined in cppsample.obj
a.obj : error LNK2005: "public: __thiscall A::~A(void)" (??1A@@QAE@XZ) already defined in cppsample.obj
a.obj : error LNK2005: "public: int __thiscall A::getBV(void)" (?getBV@A@@QAEHXZ) already defined in cppsample.obj
b.obj : error LNK2005: "public: __thiscall B::B(void)" (??0B@@QAE@XZ) already defined in cppsample.obj
b.obj : error LNK2005: "public: __thiscall B::~B(void)" (??1B@@QAE@XZ) already defined in cppsample.obj
b.obj : error LNK2005: "public: int __thiscall B::getAV(void)" (?getAV@B@@QAEHXZ) already defined in cppsample.obj
Release/cppsample.exe : fatal error LNK1169: one or more multiply defined symbols found

---

cppsample.cpp

Code:

---

//This is the main file.
//Includes (Unused)
/*
These include files are not included but may be included later.
#include <limits>                                //Limits
#include <fstream>                                //File stream for dealing with files.
*/

//Includes (Standard)
#include <cstdio>                                //C Standard Input/Output
#include <cstdlib>                                //C Standard Library
#include <iostream>                                //Input/Output Stream
#include <string>                                //C++ Strings
using namespace std;                        //Use Standard Namespace

//Includes (custom)
#include "a.cpp"
#include "b.cpp"

//Defines
#define CURRENT_EXPERIMENT "This program will try to get two classes to reference each other."

//Type Definitions
typedef short unsigned int sui;        //Shorthand form of numbers from 0 to 65,535.
typedef short int si;                        //Shorthand form of numbers from -32,768 to 32,767.

int main(int iNumberOfArgs, char* psArgs[])
{
        cout << CURRENT_EXPERIMENT << "\n";
        system("PAUSE");
        A hi;
        cout << hi.iOfA << "\n";
        system("PAUSE");
        return 0;
}

---

a.cpp

Code:

---

#include "a.h"
#include "b.h"
A::A()
{
        iOfA=1;
        pToB=0;
}
A::~A()
{
}
int A::getBV()
{
        return pToB->iOfB;
}

---

b.cpp

Code:

---

#include "a.h"
#include "b.h"

B::B()
{
        iOfB=2;
        pToA=0;
}
B::~B()
{
}
int B::getAV()
{
        return pToA->iOfA;
}

---

a.h

Code:

---

#ifndef A_ADDED
#define A_ADDED
#ifndef B_ADDED
class B;
#endif
class A
{
public:
        A();
        ~A();
        int getBV();
        int iOfA;
private:
        B* pToB;
};
#endif

---

b.h

Code:

---

#ifndef B_ADDED
#define B_ADDED
#ifndef A_ADDED
class A;
#endif
class B
{
public:
        B();
        ~B();
        int getAV();
        int iOfB;
private:
        A* pToA;
};
#endif

---

wow... you need to not use templates... or at least not that one... here's what you can cut out of your main program:

Code:

---

//This is the main file.

//Includes (Standard)
//here you included c headers for I/O, which aren't needed if you're using c++
#include <iostream>                                //Input/Output Stream
#include <string>                                //C++ Strings
using namespace std;                        //Use Standard Namespace

//Includes (custom)
#include "a.cpp"
#include "b.cpp"

//no need to make new int size definitions... IMO, short int is a whole lot
//clearer to most people than si or sui for short unsigned int...

int main()
{
        cout << CURRENT_EXPERIMENT << "\n";
        cin.get();        //pause removed - creates possible security holes
        A hi;
        cout << hi.iOfA << "\n";
        cin.get();        //see above comment
        return 0;
}

---

Thank you for the tips, I've adapted the main .cpp for that, but there are still linker errors.

If anyone else can help me solve this I'd be grateful.

>> #include "a.cpp"

You don't include cpp files (unless you are doing template programming, which you aren't). That's your problem. You should be including the header files (a.h and b.h).

>> #ifndef B_ADDED

That is not necessary in your a.h file, and the same is true for the #ifndef A_ADDED in your b.h file. Just use one include guard specific to that particular file.

Thank you, I have solved my problem now.