How to do gc without gc

Usually we do things like this

int main() {
    int* A = new int;
    free(A);
}

Sometimes we delete it to early

int main() {
    int* A = new int;
    free(A);
    cout << *A << endl;
}

Undefine behavior

Sometimes we delete it to late

int main() {
    int* A = new int;
    cout << *A << endl;
}

Memory leak

Reference counting

int main() {
    std::shared_ptr<int> p = std::make_shared<int>(2);
    cout << *p << endl; //2
    *p = 5;
    cout << *p << endl; //5
}
 

How it works?
by reference counting
Let's do a exam.

class test {
    public:
    test() {cout << "I burn!" << endl;}
    ~test() {cout << "I die!" << endl;}
};
 
int main() {
    test* p = new test;
    cout << "end program" << endl;
    return 0;
}

I burn!
end program

class test {
    public:
    test() {cout << "I burn!" << endl;}
    ~test() {cout << "I die!" << endl;}
};
 
int main() {
    std::shared_ptr<test> p = std::make_shared<test>();
    cout << "end program" << endl;
    return 0;
}

I burn!
end program
I die!

class test {
    public:
    test() {cout << "I burn!" << endl;}
    ~test() {cout << "I die!" << endl;}
};
 
int main() {
    {
        std::shared_ptr<test> p = std::make_shared<test>();
    }
    cout << "end program" << endl;
    return 0;
}

I burn!
I die!
end program

we have a obj, count = 0

when value = obj, count++

when value is destroy, count--

when count == 0, free(obj)

https://code.sololearn.com/c2rR1h9G9ehg