C++ - Basic garbage collector using reference counting

Question

Ok, I'm trying to implement a garbage collector in C++ (a very basic one) using the concept of reference counting, and it works but there is something that I don't understand.
I have two classes:

a class called GC, basically what it does is just incrementing and decrementing the reference counter

a class named TObject which plays the role of a smart pointer(I overloaded the * and -> operators, and also the = operator)

Here is the code below: GC.cpp

#include <iostream>

using namespace std;

class GC {
public:
    GC(){
        this->refCount = 0;//Initialisation du compteur à zero
    }

    void incrementRef(){
        this->refCount++;//Incrémentation du compteur de references
    }

    int decrementRef(){
        return this->refCount--;//Décrementation du compteur de references
    }

    int getCounter(){//Getter du compteur de references
        return refCount;
    }
    ~GC(){}

private:
    int refCount; //Compteur de references
};

TObject.cpp:

#include <iostream>
#include "GC.cpp"

using namespace std;

template <class T>
class TObject {

T *p;
GC *gc;

public:
    TObject(T *p){
        cout<<"refobject"<<endl;
        this->p = p;
        gc = new GC();
        this->gc->incrementRef();
    }

    virtual ~TObject(){//Destructeur
        cout<<"delete TObject"<<endl;
        if(this->gc->decrementRef() == 0){
            delete p;
            delete gc;
        }
    }

    T* operator->(){//Surcharge de l'opérateur d'indirection
        return p;
    }

    T& operator*() const {//Surchage de l'opérateur
        return *p;
    }

    TObject<T>& operator=(const TObject<T> &t){
        if(this->gc->decrementRef() == 0){
            delete p;
            delete gc;
        }
        this->p = t.p;
        this->gc = t.gc;
        this->gc->incrementRef();
        return *this;
    }

    GC getGC(){
        return *gc;
    }
};

And here how I tested it in main:

TObject<int> t(new int(2));
cout<<"t1 counter: "<<t.getGC().getCounter()<<endl;//Displays 1
TObject<int> t2(NULL);
cout<<"t2 counter: "<<t2.getGC().getCounter()<<endl;//Displays 1
t2 = t;
cout<<"t1 counter: "<<t.getGC().getCounter()<<endl;//Displays 2, why?
cout<<"t2 counter: "<<t2.getGC().getCounter()<<endl;//Displays 2

I don't get it, I copied t in t2 and I did not update t1! Why its reference counter was updated too?

Answer 1

It's because, both t and t2 are sharing same gc instance. Look at your overloaded = operator method :-

TObject<T>& operator=(const TObject<T> &t)
{
   if(this->gc->decrementRef() == 0)
   {
        delete p;
        delete gc;
   }
   this->p = t.p;
   this->gc = t.gc;  // you are using same gc. Instead, you must be using
                     //  this->gc = new GC(); 
   this->gc->incrementRef();
   return *this;
}