Virtual destructor test

destructor_test.cc

/*
 * Virtual destructor test
 * -----------------------
 * compile using:
 *   cc -std=c++11 -o destructor_test destructor_test.cc -lstdc++
 *
 * when class `A` does not define a virtual destructor the program prints:
 *   data constructed
 * rationale:
 *   when a pointer typed to class `A` is used to delete an instance of class
 *   `B` (which is a subclass of `A`) the instance is not destructed properly
 *   as only the `A`'s destructor is called
 *
 * when class `A` _does_ define a virtual destructor the program prints:
 *   data constructed
 *   data destructed
 * rationale:
 *   a default destructor for class `B` is generated by the compiler and since
 *   the base class `A` declares a virtual destructor the generated destructor
 *   overrides that from the base class, so when a pointer typed to class `A`
 *   is used to delete an instance of class `B` the instance is destructed
 *   properly as the `B`'s destructor is called
 */

#include <iostream>

class A {
public:
    virtual ~A() = default;
};

template <typename T>
class B : public A {
    T data;
};

class D {
public:
    D() {
        std::cout << "data constructed" << std::endl;
    }

    ~D() {
        std::cout << "data destructed" << std::endl;
    }
};

int main(int argc, char *argv[]) {
    A *a_p = new B<D>;
    delete a_p;

    return 0;
}