C++ destructor not working as intended

Question

I'm writing an operating system in C++. I do not have the std libs at my disposal (so I'm not sure if this works normally with std libs). It appears that if I delete an object, it only calls the destructor of the variable type (and it's parents).

For example:

Aa* aa = new Bb();
delete aa;

will only print "destructing Aa". Whereas

Bb* bb = new Bb();
delete bb;

will print both "destructing Bb" and "destructing Aa".

I tried to work around this issue by calling the sub class destructor in the super class destructor (as seen below).

Is there something I'm missing here, or will I have to resort to casting to the concrete type before the initial delete?

class Aa {
public:
    ~Aa();
};
class Bb : public Aa {
public:
    ~Bb() {
        log("destructing Bb");
    }
};

Aa::~Aa() {
    log("destructing Aa");

    // TODO checks if we are of type Bb
    // ((Bb*) this)->~Bb(); // uncomment to test calling sub class destructor
}

"Is there something I'm missing here" - Yes. `virtual` destructors when deleting via base object pointers. — Jesper Juhl, Jul 20 '16 at 21:18

score 3 · Accepted Answer · answered Jul 20 '16 at 21:15

3

You should make the destructor of Aa virtual:

class Aa {
public:
    virtual ~Aa();
};

This is a basic concept of c++. You can read on it here (and in many other places).

answered Jul 20 '16 at 21:15

Ohad Eytan

8,114
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I do not have access to the std lib so virtual functions do not work. – Chris Smith Jul 20 '16 at 21:25
@chris13524 vitrual defination is not part of the std lib, it's integral part of the language – Ohad Eytan Jul 20 '16 at 21:27
1

I had to add the `-fno-rtti` flag to `gcc` and now it works (still requires `virtual`). – Chris Smith Jul 20 '16 at 21:30

score 0 · Answer 2 · answered Jul 20 '16 at 21:16

0

Your "Aa" destructor is not virtual, so what you are observing is the expected behaviour.

To get the behaviour you expect, declare the destructor as virtual ~Aa() = default; .

answered Jul 20 '16 at 21:16

Jesper Juhl

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C++ destructor not working as intended

2 Answers2