destructor c++ make leak memory

Question

I'm having a hard time figuring out how this destructor call

So I have class A with virtual destructor and inline virtual clone function

class A{
public:
    A(){ }
    virtual ~A(){
        qDebug() << "Class A destructor";
    }

    inline virtual A *clone(){
        return NULL;
    }
};

Then I have sub-class B also have destructor and clone function return pointer to class A

class B : public A{
public:
    B() { }
    ~B(){
        qDebug() << "Class B destructor";
    }
    A *clone(){
        B *temp = new B();
        return static_cast<A *>(temp);
    }
};

And I have main function and test function and i start do some crazy thing about pointer

A *test(A *input){
    return input->clone();
}

int main(){

    B temp2;
    A *temp = test(&temp2);
    delete temp;

    return 0;
}

Finally if I have the output is

Class B destructor
Class A destructor
Class B destructor
Class A destructor

and if I'm not using virtual before destructor class A, I have ouput is

Class A destructor
Class B destructor
Class A destructor

So can anyone explain me why virtual make so much different

This has nothing to do with the clone function. Make a main function that contains only `A* x = new B(); delete x;` and see what happens with and without virtual destructor. — pschill, Jun 12 '18 at 09:49
https://stackoverflow.com/questions/1306778/c-virtual-pure-virtual-explained https://stackoverflow.com/questions/461203/when-to-use-virtual-destructors — Piotr Siupa, Jun 12 '18 at 09:50
`delete temp;` where dynamic type of temp is `B*` whereas static type is `A*` with non virtual destructor is UB. — Jarod42, Jun 12 '18 at 09:55

score 0 · Answer 1 · answered Jun 12 '18 at 09:48

0

When to use virtual destructors?

In few words: without virtual there is no vTable and at runtime it is impossible to find derived destructor when you call one of a base class.

answered Jun 12 '18 at 09:48

Mike Petrichenko

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destructor c++ make leak memory

1 Answers1