Deleting a derived object via a pointer to its base class

Question

I have two classes, base_class and derived_class and the following code:

base_class *ptr = new derived_class; delete ptr;

Will this code produce a memory leak? If so, how should I deal with it?

The code won't compile. I would recommend passing it through a compiler first. Better would be: base_class* ptr = new derived_class(); — Ciaran
– Ciaran, Commented Jan 7, 2012 at 10:41
If base_class hasn't a virtual destructor this will trigger undefined behavior (§5.3.5/p3) — Marco A.
– Marco A., Commented May 6, 2015 at 17:39
Refer item 7 of Effective C++ by Scott Meyers (Declare destructors virtual in polymorphic base classes). — Hari
– Hari, Commented Mar 8, 2023 at 13:22

Community · Accepted Answer · 2017-05-23 11:47:04Z

It won't leak the object you are deleting, its memory block will be freed.

If you have not declared the destructor in base_class to be virtual then it will leak any dynamically allocated objects contained within derived_class that rely on the destructor of derived_class being called to free them. This is because if the destructor is not virtual, the derived_class destructor is not called in this case. It also means that destructors of "embedded objects" within derived_class will not automatically be called, a seperate but additional problem, which can lead to further leaks and the non-execution of vital cleanup code.

In short, declare the destructor in base_class to be virtual and you can safely use the technique you have presented.

For a coded example, see:

In what kind of situation, c++ destructor will not be called?

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Deleting a derived object via a pointer to its base class

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